Clinically Oriented Anatomy, 5th Edition - 2. Abdomen

7/23/2019 Clinically Oriented Anatomy, 5th Edition - 2. Abdomen

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Authors: Moore, Keith L.; Dalley, Arthur F.

Tit le: C l in i c a l l y O r i e n t e d A n a t o m y , 5 t h E d i t i o n

Copyr ight 2006 Lippincott Wil l iams & Wilkins

> Table of Contents > 2 - Abdomen

2

Abdomen

The abdomenis the part of the trunk between the thorax and the pe lvis (F ig. 2.1).

It is a f lexib le , dynamic conta iner , hous ing m ost of the organs of the d igest ive system and part of the urogenita l system.

Conta inment of the abdominal organs and the ir contents is provided by musculoaponeurot ic wal ls anterolatera lly, the

diaphragm super ior ly, an d the musc les of the pe lvis infer ior ly, which are suspended between and supported by two bony

r ings (the infer ior margin of the thorac ic ske leton super ior ly and pe lvic g ird le infer ior ly) l inked by a semir ig id lumbar

vertebra l column in the poster ior abdominal wal l . The abdomen is thus able to enc lose and protect i ts contents whi le

a l lowing the f lexib i l i ty between the m ore r ig id thorax and p e lvis required by respirat ion, posture, and locomotion. Th rough

voluntary or re f lexive contract ion, i ts muscular roof , anterolatera l wal ls , and f loor can ra ise internal ( intra-abdominal)

pressure to a id expuls ion f rom the abdominopelvic cavity or f rom t he adjacent thorac ic cavity, expuls ion of a ir f rom the

thorac ic cavity ( lungs and bronchi) or of f lu id (e.g., ur ine or vomitus), f latus, feces, or fetuses f rom the abdominopelvic

cav i ty .

Overview: Walls, Cavities, Regions, and PlanesThe dynami c musculoaponeurot ic abdominal wal ls not only contract to increase intra-abdominal pressure but a lsodis tend cons iderably, accommodating expans ions caused by ingest ion, pregnancy, fat depos it ion, or pathology. T he

antero latera l abdomina l wa l ls and several organs lying against the p oster io r w al lare covered on the ir internal aspects

with a serous membrane or p er it one um(serosa) that also ref lects ( turns sharp ly and continues) onto the conta ined

abdominal v iscera(L. sof t p arts , internal organs), such as the stomac h, intest ine, l iver , and sp leen. Thus a bursal sac

or l ined potentia l space (the pe ri ton eal cav it y) is formed between the wal ls and the viscera that normal ly conta ins only

enough extrace l lu lar (par ieta l) f lu id to lubr icate the mem brane cover ing most of the sur faces of the structures forming or

occupying the abdom inal cavity. Viscera l movement assoc iated with d igest ion occurs free ly, and the double- layered

ref lect ions of per itoneum pass ing between the wal ls and the viscera provide passage for the b lood vesse ls , lymphatics ,

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Figure 2.1. Overview of v iscera of thorax and abdomen in situ.

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and nerves. Var iab le amounts of fat may a lso occur between the wal ls and viscera and the per itoneum l in ing them.

The abdominal cavity forms the superior and major part of the abdominopelvic cavity (F ig. 2.2), the continuous cavity

that extends between the thoracic d iaphragm and the pe lvi c di ap hr ag m . The abdominal cavity has no f loor of its own

because it is continuous with the pe lv i c cav it y .The p lane of the pe lv ic inl et(super ior pe lvic aperture) arb itrar i ly, but n ot

phys ica l ly, separates the abdominal and the pe lvic cavit ies . The abdominal c avity extends super ior ly into the

osseocart i lag inous thoracic cageto the 4th i ntercosta l space (F ig. 2.1). Consequently, the more super ior ly p laced

abdominal organs (sp leen, l iver , part of t he kidneys, and s tomach) are protected by the thorac ic cage. Th e greater pe lvis

(expanded part of the pe lvis super ior to the pe lvic in let) supports and part ly protects the l ower abdominal viscera (part of

the i leum, cecum, and s igmoid colon).

In summary, the abdominal cavity is

l The m ajor part of the abdominopelvic cavity.

l Located between the d iaphragm and the pe lvic in let.

l Separated f rom the thorac ic cavity by the thorac ic d iaphragm.

l Continuous infer ior ly with the pe lvic cavity.

l Under cover of the thorac ic cage super ior ly.

l Supported and part ia l ly protected infer ior ly by the greater pe lvis .

l Enc losed anterolatera l ly by mult i- layered, musculoaponeurot ic , abdominal wal ls .

l The locat ion of most d igest ive organs, parts of the urogenita l system (kidneys and most of the ureters), and the

spleen.

Cl in ic ians refer to nine regions of the abdominal cavity to descr ibe the locat ion of abdominal organs, pains, or p athologies

(Table 2.1A& B) . The nine regions are de l ineated by four p lanes: two sagitta l (vert ica l) and two transverse (hor izonta l)

p lanes. The two sagitta l p lanes are usual ly the midclavicular planesthat pass f rom the midpoint of the c lavic les

(approximate ly 9 cm f rom the midl ine) to the midinguinal points , midpoints of the l ines jo ining the anterior superior

i l iac sp ine (ASIS) and the superior edge of the pu b ic sy mph ys is(L. symphysis pub is) on each s ide. Sometimes p lanes

intersecting the semilunar l ines , the sur face m arkings (shal low grooves) of the latera l borders of the rectus abdominis

musc les , are used as t he vert ica l de l ineations. However, this is pract ica l only in lean people who have d is t inct sur face

def in it ion of the under lying musc les .

There is a lso some var iat ion in the transverse p lanes that are used to def ine abdominal reg ions. Most comm only, the

transverse planes are the subcostal plane, pass ing through the infer ior border of the 10th costa l cart i lage on each s ide,

and

the transtubercular plane, pass ing through the i l iac tuberc les (approximate ly 5 cm poster ior to the ASIS on each s ide)

and the body of the L5 vertebra. Both of these p lanes have the advantage of intersect ing palpable s tructures. However,

other c l in ic ians use the transpylor ic and intersp inous p lanes to establ ish th e nine regions. The transpyloric plane,

extrapolated midway between the superior borders of the manubr ium of the sternum and the pubic symphys is ( typ ica l ly

the L1 vertebra l leve l) , common ly transects the py lo rus ( the d is ta l, more tubular part of the s tomach) when the patient is

recumbent (supine or prone) (Fig. 2.1). Because the viscera sag with the pull of gravity, the pylorus usually lies at a

lower leve l when the ind ividual is s tanding e rect. The transpylor ic p lane is a useful landmark because it a lso transects

many ot her important s tructures: the fundus of the gal lb ladder, neck of the pancreas, or ig ins of the super ior mesenter ic

artery (SMA) and porta l ve in, root of the transverse mesocolon, duodenojejunal junct ion, and hi la of the kidneys. Th e

interspinous planepasses through the eas i ly palpated ASIS of each s ide (Table 2.1B) .

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Figure 2.2. Abdominopelvic cavity.The body has been sect ioned in the median p lane to show the abdominal and

pelvic cavit ies as subdivis ions of the continuous abdominopelvic cavity.

Table 2.1. Abdominal Regions (A), Reference Planes (B), and Quadrants (C)





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For more general c l in ica l descr ipt ions, four quadrants of the abdominal cavity (r ight and le f t upper and lower quadrants)

are def ined by t wo readi ly def ined p lanes: (1) the transverse transumbil ical plane, pass ing through the umbil icus (and

the intervertebra l [IV] d isc between the L3 and L4 vertebrae), d ivid ing it into u pper and lower halves, and (2) t he vert ica l

median plane, pass ing longitudinal ly through th e body, d ivid ing it into r igh t and le f t ha lves (Table 2.1C) .

It is im portant to know w hat organs are located in each abdominal reg ion or quadrant so that one knows where to

auscultate, percuss, and palpate them (Table 2.1). K nowledge of the locat ion of the organs is a l so essentia l for record ingf ind ings dur ing a phys ica l ex amination.

Anterolateral Abdominal WallAlthough the abdominal wal l is continuous, i t is subdivided into the anterior wal l , r ight and left la tera l wa l ls( f lanks ) , and

p os teri or wa llfor descr ipt ive purposes (F ig. 2.3). The wal l is musculoaponeurot ic, except for the poster ior wal l , which

inc ludes the lumbar vertebra l column. Because the boundary b etween the anter ior and the l ateral wal l s is indef inite , the

term anterolateral abdominal wall is often used; some structures, such as the muscles and cutaneous nerves, are in

both the anter ior and the latera l walls . The anterolatera l abdominal wal l ext ends from the thorac ic cage to the pelvis .





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Dur ing a phys ica l exam ination, the anterolatera l wal l is inspected, palpated, percussed, and auscultated. Surgeons usual ly

inc ise this wal l dur ing abdominal surgery. The anterolatera l abdominal wal l is bounded super ior ly by the cart i lages of the

7th10th r ibs and the xiphoid process of the sternum and infer ior ly by the inguinal l igament and the super ior margins

of the anterolatera l aspects of the pe lvic g ird le ( i liac crests , pubic crests , and pubic symphys is) (F ig. 2.4A ).

The wal l cons i s ts of skin and subcutaneous t issue (super fic ia l fasc ia) composed mainly of fat, musc les and the ir

aponeuroses and deep fasc ia, extraper itoneal fat, and par ietal per itoneum (F ig. 2.4B) . The skin attaches loose ly to the

subcutaneous t issue, except at the umbil icus, where it adheres f irmly. Most of the anterolatera l wal l inc ludes th ree

musculotendinous layers; the f ibers of each layer run in d i f ferent d irect ions. This three-p ly s tructure is s imi lar to that of

the intercosta l spaces in th e thorax (see Chapter 1).

F a sc i a o f t h e A n t e r o l a t e r a l A b d o m i n a l W a l l

The subcutaneous t issue over most of the wal l inc ludes a var iab le amount of fat. It is a major s ite of fat s torage. Males

are espec ia l ly susceptib le to subcutaneous accumulat ion in t he lower ant er ior abdominal wal l and may havedisproport ional amounts of fat here whi le having more normal amounts e lsewhere. In morbid obes ity, the fat is many

inches thick, often forming one or more sagging folds (L. pa nn ic ul i ; s ingular = pa nni cu lu s , apron). Inferior to the

umbilicus, the deepest part of the subcutaneous tissue is reinforced by many elastic and collagen f ibers, so the

subcutaneous t issue here has two layers: a superficial fatty layer (Camper fasc ia) and a deep membranous layer

(Scarpa fasc ia). The mem branous layer continues infer ior ly into the per ineal reg ion as the super f ic ia l per ineal fasc ia

(Col les fasc ia), but not into the thighs. In many ind ividuals , the

membranous layer is suf f ic ient ly complete that f lu ids escaping f rom a ruptured vesse l or urethra (b lood and/or ur ine) may

accumulate deep to i t (see the c l in ica l corre lat ion [b lue] box Rupture of t he Urethra and Extravasation of Ur ine, in

Chapter 3).

Figure 2.3. Subdivisions of abdominal wall . This transverse sect ion of the abdomen demonstrates var ious as pects

of the wal l and its components .

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Superf ic ia l , intermediate, and deep layers of invest ing fascia cover the external aspects of the three muscle layers of

the anterolatera l abdominal wal l and the ir aponeuroses( f lat expanded tendons) and cannot be eas i ly separated f rom

them. Th e invest ing fascias here are extremely thin, be ing represented mostly by the epimys ium super f ic ia l to or between

musc les . The internal aspect of the abdominal wal l is l ined with a membranous sheet of varying thickness ca l led the

endoabdominal fascia.

Although continuous, d i f ferent parts of this fasc ia are named accord ing to the musc le or apon euros is i t is l in ing. The

port ion l in ing t he deep sur face of the transverse abdominal musc le and its aponeuros is , the transversalis fascia, is

re lat ive ly f irm. The l in ing of the abdominal cavity, the pa ri e ta l pe r it on eum, is internal to the transversal is fasc ia and is

separated from it by a variable amount of extraperitoneal fat .

Clinical Significance of Fascia and Fascial Spaces of Abdominal Wall

Liposuction is a surg ical m ethod for removing unwanted subcutaneous fat us ing a percutaneous ly p laced suct ion tube

and high vacuum pressure. The tubes are inserted subdermal ly through smal l skin inc is ions.

When c los ing lower abdo minal skin inc i s ions, surgeons inc lude the membranous layer of subcutaneous t i ssue when

sutur ing because of i ts s trength. Between this layer and the deep fasc ia cover ing the rectus abdominis and external

obl ique musc les is a potentia l space where f lu id may accumulate (e.g., ur ine f rom a ruptured urethra). A lthough there are

no barr iers (other than gravity) to prevent f lu id f rom spreading super ior ly f rom this space, i t cannot spread infer ior ly into

the thigh because the membranous layer fuses with the deep fascia of the thigh ( fascia la ta) a long a l ine approximate ly2.5 cm infer ior and para l le l to the inguinal l igam ent.

The potentia l or fat- f i l led space between the endoabdominal fasc ia is of spec ia l importance in s urgery. It provides a p lane

that can be opened, enabl ing the surgeon to approach structures on or in the anter ior aspect of t he poster ior abdominal

wal l , such as the kidneys or bodies of lumbar vertebrae, without enter ing the membranous per itoneal sac conta ining the

abdominal viscera. Thus the r isk of contamination is minimized. An an terolatera l part of this potentia l space between the

transversal is fasc ia and the par ieta l per itoneum (the space of Bogros) is used for p lac ing prostheses, for example, when

repair ing inguinal hernias (Skandalakis et a l . , 1996) (F ig. 2 .12A & B).

Figure 2.4. Abdominal contents, undisturbed, and layers of anterolateral abdominal wall . A. The anter ior

abdominal wal l an d sof t t issues of the anter ior thorac ic wal l have been removed. Most of the intest ine is covered by

the apron- l ike greater omentum, a per itoneal fo ld hanging f rom the stomach. B .Layers of th e anterolatera l

abdominal wal l , inc lud ing the tr i laminar f lat musc les , are shown.

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The Bottom Line

The fasc ia of t he anterolateral abdominal wal l cons is ts of subcutaneous (super f ic ial) , invest ing (deep), and intra-

abdominal (endoabdominal) portions. The subcutaneous layer is modif ied in the lower abdomen to include a superf ic ial

fatty layer an d a deep membranous layer . The super f ic ia l fatty layer is spec ia l ized, part icular ly in males, for l ip id s torage,

whereas the deep m embranous layer is suf f ic ient ly complete to compartmental ize extravasated f lu ids (b lood or ur ine) and

al low p lacement of sutures dur ing surgery. The invest ing layer is typ ica l of deep fasc ias ensheathing voluntary m usc les ,

and here ref lects the tr i laminar arrangement of the f lat abdominal musc les and the ir aponeuroses. The endoabdominal

fasc ia is of part icular importance i n surgery, enabl ing the establ ishment of an extraper itoneal space that a l lows anter ior

access to retroper itoneal s tructures (e.g., kidneys, ureters and bodies of lumbar vertebra) without enter ing the per itonealcav i ty .

M u s c l e s o f t h e A n t e r o l a t e r a l A b d o m i n a l W a l l

There are f ive ( b i latera lly paired) musc les in the anterolatera l abdominal wal l (F ig. 2.3): three f lat musc les and two

vert ica l musc les . The ir attachm ents, nerve supply, and ma in act ions are l is ted in Table 2.2. T he three f lat musc les are the

externa l ob l ique, interna l ob l ique, and transverse abdomina l(F ig. 2.4). The musc le f ibers of these concentr ic layers

cr isscross each other , with the f ibers of the outer two layers running d iagonal ly and perpendicular to each other for the

main part, and the f ibers of the deep layer running transverse ly (F ig. 2.5A). All three f lat muscles are continued anteriorly

and m edia l ly as s trong, sheet- l ike aponeuroses. Between the midc lavicular l ine (MCL) and the mid l ine, the aponeuroses

form the tough, apon eurot ic , tendinous rectus sheath enc los ing the rectus abdominis musc le (F ig. 2.5B). The aponeuroses

then interweave with the ir fe l lows of the oppos ite s ide, forming a mid l ine raphe ( G. rhaphe , suture, seam), the l inea a lba

(L. white l ine), which extends f rom the xiphoid process to the pubic symphys is . Th e decussat ion and interweaving of the

f ibers here is not only between r ight and le f t s ides but a lso between super f ic ial and in termediate and intermediate and

deep layers.

The tw o vert ica l musc les of the anterolatera l abdominal wal l , c onta ined within the rectus sheath, are the rectus abdominis

and py ra m idal i s.

External Oblique Muscle

The external oblique muscleis the largest and m ost super f ic ia l of the three f lat anterolatera l abdominal musc les (F ig.

2.6). The attachments, nerve supply, and main ac t ions of the external ob l ique are presented in Table 2.2. In contrast to

the two deeper layers , the external ob l ique does not or ig inate poster ior ly f rom the thoracolumbar fasc ia; i t s posteriormost

f ibers ( the thickest part of t he musc le) have a f ree edge where they span between its costa l or ig in an d the i l iac crest

(Table 2.2D ) . The f leshy part of the musc le contr ibutes pr imar i ly to the latera l part of th e abdominal wal l . Its aponeuros is

contr ibutes to the anter ior part of the wal l .

Although the poster iormost f ibers f rom r ib 12 are nearly vert ica l as they run to the i l iac crest, more anter ior f ibers fan

out, taking an increas ingly media l d irect ion, so that most of the f leshy f ibers run inferomedia l ly in the same direct ion

as the f ingers do when t he hands are in one 's s i de pocketswith the most anter ior and super ior f ibers approaching a

hor izonta l course. The mu sc le f ibers become aponeurot ic

approximate ly at the MCL media l ly and at the spinoumbil ical l ine( l ine running f rom the umbil icus to the ASIS)

infer ior ly, forming a sheet of tendinous f ibers that decussate at the l inea a lba, most b ecoming continuous with tendinous

f ibers of the contra latera l internal ob l ique (F ig. 2.5A ) . Thus the contra latera l external and internal ob l ique m usc lestogether form a digastr ic musc le, a two-bel l ied musc le shar ing a common centra l tendon that works as a unit. For

example, the r ight external ob l ique and le f t internal ob l ique work together when f lexing and rotat ing to br ing the r ight

shoulder toward the le f t hip ( tors ional m ovement of trunk).

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Table 2.2. Muscles of the Anterolateral Abdominal Wall





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Infer ior ly, the external ob l ique aponeuros is attaches to the pubic crest media l to t he pubic tubercle.The infer ior

margin of the external ob l ique aponeuros is is thickened as an

Musc le Or ig in Insert ion Innervation Main Action a

Rectus

abdominis

(A)

Pubic symphys is and

pubic crest

Xiphoid process

and 5th7th

costal cartilages

Thoracoabdominal

nerves (anter ior rami

of infer ior 6 thorac ic

nerves)

F lexes trunk ( lumbar

vertebrae) and

compresses

abdominal viscera;b

stabi l izes and

controls t i l t of pe lvis

(anti lordos is)

Transverse

abdominal

(B)

Internal sur faces of

7th12th costa l

cart i lages,

thoracolumbar fasc ia,

i l iac crest, and latera lthird of inguinal

l igament

Linea a lba with

aponeurosis of

internal ob l ique,

pubic crest, and

pecten pubis viaconjoint tendon

Thoracoabdominal

nerves (anter ior rami

of infer ior 6 thorac ic

nerves) and f irs t

lumbar nerves

Compresses and

supports abdominal

viscerab

Internal

oblique (C)

Thoracolumbar fasc ia,

anter ior two-thirds of

i l iac crest, and latera l

half of inguinal

l igament

Inferior borders of

10th12th r ibs ,

l inea a lba, and

pecten pubis via

conjoint tendon

Compress and

support abdominal

viscera,b f lex and

rotate trunk

External

oblique (D)

External sur faces of

5th12th r ibs

Linea and a lba,

pubic tubercle,

and anterior half

of il iac crest

Thoracoabdominal

nerves (inferior 5

[T7T11] thorac ic

nerves) and subcosta l

nerve

a Approximate ly 80% of people have an ins ignif icant musc le, the pyramida l is,which is located in t he rectus

sheath anter ior to the most inferior part of the rectus abdominis . It extends f rom the pubic crest of the hip bone

to the l inea a lba. This smal l musc le draws down on the l inea a lba.b In so doing, these musc les act as antagonis ts of the d iaphragm to produce expirat ion.

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undercurving f ibrous band with a free posterior edge that spans between the ASIS and the pubic tubercle as the inguina l

l i gament (Poupart l igament) (F igs . 2.6B and 2.7). Pa lpate your inguinal l igament by press ing deeply into the center of the

crease between the thigh and trunk and moving the fingert ips up and down. Infer ior ly the inguinal l igament is continuous

with the deep fasc ia of the thigh. The inguinal l igament is therefore not a f reestanding structure, a lthoughas a useful

landmarkit is f requently depic ted as such. It serves as a ret inaculum (a reta ining band) for the structures pass ing

deep to i t to enter the thi gh ( i l iopsoas musc le and femoral vesse ls and nerve). The l atera l port ion of the inguinal l igament

provides the or ig in for the infer ior parts of the two deeper anterolatera l abdominal musc les . The modif icat ions andattachments of the inguinal l igament and of the inferomedia l port ions of the aponeuroses of the anterolatera l abdominal

wal l musc les are complex and most s i gnif icant in re lat ion to the i nguinal canal; they are d iscussed in deta i l with the

inguinal reg ion ( later in this chapter) .

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Figure 2.5. Structure of anterolateral abdominal wall . A. Intramuscular and interm uscular f iber exchanges

within the b i laminar aponeuroses of the external and the internal ob l ique m usc les are shown. B. Transverse sect ions

of the wal l super ior and infer ior to the u mbil icus show the m akeup of the rectus sheath.





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Internal Oblique Muscle

The intermediate of the three f lat abdominal musc les , the internal ob l ique muscleis a thin mu scular sheet that fans out

ante romed ia lly (F igs . 2 .7 and 2.8A ; Table 2.2B). Except for its lowermost f ibers, which arise from the lateral half of the

inguinal l igament, i ts f leshy f ibers run perpendicular to those of the external ob l ique, running superomedia l ly ( l ike your

f ingers when the hand is p laced over your chest) . Its f ibers a lso become aponeurot ic in roughly the sam e (midc lavicular)

l ine as the external ob l ique and part ic ipate in the formation of the rectus sheath. The attachments, nerve supply, and

main act ions of the internal ob l ique are l is ted in Table 2.2.

Figure 2.6. Anterolateral abdominal wall . A. In this super f ic ia l d issection, the anter ior layer of the rectus sheath

is re f lected on t he le f t s ide. Observe the anter ior cutaneous nerves (T7T12) p ierc ing the rectus abdominis and the

anter ior layer of the rectus sheath. B. The three f lat abdominal musc les and th e formation of the inguinal l igament

are demonstrated.





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Figure 2.7. Inferior abdominal wall and inguinal region of a male. The aponeuros is of the external ob l ique ispart ly cut away and the spermatic cord has been cut and removed f rom the inguinal canal. Th e ref lected (ref lex)

inguinal l igament is formed by aponeurot ic f ibers of the external ob l ique. The i l iohypogastr ic and i l io inguinal nerves

(branches of the f irs t l umbar nerve) pass between the external and the internal ob l ique musc les . The i l io inguinal

nerve traverses the inguinal canal and is vulnerable dur ing repair of an inguinal hernia.

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Figure 2.8. Formation of rectus sheath and neurovascular structures of anterolateral abdominal wall . A.I n

this deep d issect ion, the f leshy port ion of the external ob l ique is exc ised on the r ight s ide, but i ts aponeuros is and

the anter ior wal l of the rectus sheath are intact. Th e anter ior wal l of the sheath and the rectus abdom inis are

removed on the le f t s ide so that the poster ior wal l of the sheath is seen. Latera l to the le f t rectus sheath, the f leshy

part of the internal ob l ique has been cut longitudinal ly; the edges of t he cut are retracted to rev eal the

thoracoabdominal nerves cours ing in the neurovascular p lane between th e internal ob l ique and the transverse

abdominal. B. A sagitta l sect ion through the rectus sheath of the anter ior abdominal wal l is shown. The anastomos is

between the superior and the inferior epigastric arteries indirectly unites the arteries of the upper limb (subclavian





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Transverse Abdominal Muscle

The f ibers of the transverse abdominal muscle (L. musculus transversus abdominis ) , the innermost of the three f lat

abdominal musc les (F ig. 2.6B, Table 2.2B) , run more or less transversal ly, except for the infer ior ones, which run para l le l

to those of the internal ob l ique. This transverse, c ircumferentia l or ientat ion is ideal for compress ing the abdomi nal

contents , increas ing intra-abdominal pressure. The f ibers of the transverse abdominal musc le a lso end in an aponeuros is ,

which contr ibutes to the formation of the rectus sheath (F ig. 2.8). The attachments, n erve supply, and main act ions of the

transverse abdominal m usc le are l is ted in Table 2.2.

Between the internal ob l ique and the transverse abdominal musc les is a neurovascular plane , which corresponds with a

s imilar p lane in the intercosta l spaces. In b oth regions, the p lane l ies between the middle and t he deepest layers of

musc le (F ig. 2.8A) . The neurovascular p lane of the anterolatera l abdominal wal l conta ins the nerves and arter ies

supplying the anterolatera l abdominal wal l . In the anter ior part of the abdominal wal l , the nerves and vesse ls leave the

neurovascular p lane and l ie mostly in the subcutaneous t issue.

Rectus Abdominis Muscle

A long, broad, s trap- l ike musc le, the rectus abdominis (L. rec tus, s tra ight) is the pr inc ipa l vert ica l musc le of the

anter ior abdominal wal l (F igs . 2.6Aand 2.8B ; Table 2.2A) . The attachments, nerve supply, and main act ions of the rectus

abdominis are l is ted in Table 2.2. The paired rectus musc les , separated by the l inea a lba, l ie c lose together infer ior ly. The

rectus abdominis is three t imes as wide super ior ly as infer ior ly; i t is broad and thin s uper ior ly and narrow and thick

infer ior ly. Most of the rectus abdominis is enc losed in the rectus sheath. The rectus musc le is anchored transversely by

attachment to the anter ior layer of the rectus sheath at three or more tendinous intersect ions.When tensed in

muscular people, the stretches of musc le between the tendinous intersect ions bulge outward. The intersect ions, ind icated

by grooves in the skin between the muscular bulges, usual ly occur at the leve l of the xiphoid process, umbi l icus, and

halfway between these structures.

Pyramidalis

The pyramidalis is a smal l tr iangular musc le that is absent in approxim ate ly 20% of people. It l ies anter ior to the

infer ior part of the rectus abdominis and attaches to t he anter ior sur face of the pubis and the anter ior pubic l igament. It

ends in the l inea a lba, w hich is espec ia l ly thickened for a var iab le d is tance super ior to t he pubic symph ys is . The

pyramidal is tenses the l inea a lba; when present, surgeons use the attachm ent of the pyramidal is to the l inea a lba as a

landmark for an accurate median abdominal inc is ion (Skandalakis et a l . , 1995).

Rectus Sheath, L inea Alba, an d Umbilicus

The rectus sheath is the s trong, incomplete f ibrous compartment of the rectus abdominis and pyramidal is m usc les (F igs .

2.5, 2.6, 2.7, and 2.8). Also found in the rectus sheath are the super ior and infer ior ep igastr ic ar ter ies and ve ins,

lymphatic v esse ls , and d is ta l port ions of the t horacoabdominal nerves (abdominal port ions of the anter ior rami of sp inalnerves T7T12). The sheath is formed by the decussat ion and interweaving of the aponeuroses of the f lat abdominal

musc les . The external ob l ique aponeuros is contr ibutes to the anter ior w al l of the sheath t hroughout i ts length. The

super ior two thirds of the internal ob l ique aponeuros is sp l i ts into two layers , or laminae, at the latera l border of the

rectus abdominis; one lamina pass ing anter ior to the m usc le and the other pass ing poster ior to i t . The anter ior lamina

jo in s th e apon eu ro si s of the ext er na l ob l ique to fo rm th e a nte ri or layer of th e rec tus sh eat h. Th e po st er ior lam ina joi n s

the aponeuros is of the transverse abdominal musc le to form the poster ior layer of the rectus sheath.

Beginning at approximate ly one third of t he d is tance f rom the um bil icus to the pubic crest, the aponeuroses of the three

f lat musc les pass anter ior to the rectus abdomi nis to form the anter ior layer of the rectus sheath, leaving only t he

re lat ive ly t hin transversal is fasc ia to cover the rectus abdominis poster ior ly. A crescentic l ine, ca l led the arcuate l ine,

demarcates the trans it ion between the aponeurot ic poster ior wal l of the sheath cover ing the super ior three quarters of the

rectus and the transversal is fasc ia cover ing the infer ior quarter . Throughout t he length of the sheath, t he f ibers of the

anterior and posterior layers of the sheath interlace in the anterior median line to form the complex linea alba.

The poster ior layer of the rectus sheath is a lso def ic ient super ior to the costa l margin because the transverse abdominal

musc le passes internal to t he costa l cart i lages and the internal ob l ique attaches to the costa l margin. Hence, super ior to

the costa l margin, th e rectus abdominis l ies d irectly on the thorac ic wal l .

The l inea alba, running vert ica l ly the entire length of the anter ior abdominal wal l and separat ing the b i latera l rectus

sheaths, narrows infer ior to the umbil icus to the width of the publ ic symphys is and widens super iorly to t he width of the

xiphoid process. The l inea a lba transmits smal l v esse ls and nerves to the skin. I n thin m uscular people, a groove is vis ib le

in the skin over lying the l inea a lba. At i ts middle, under lying the umbil icus, the l inea a lba conta ins the umbil ical ring, a

defect in the l inea a lba t hrough which the feta l umbi l ica l vesse ls passed to and f rom t he umbil ica l cord and p lacenta. Al l

layers of t he anterolateral abdominal wal l fuse at the umbil icus. As fat accumulates in the subcutaneous t issue

postnata l ly, the skin becomes ra ised around the umbil ica l r ing and the um bil icus becomes depressed. This occurs 714

days af ter b ir th, when the atrophic umbil ica l cord falls of f .

artery) and lower l imb (external i l iac ar tery).

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Functions and Actions of the Anterolateral Abdominal Muscles

The m usc les of the anterolateral abdominal wal l:

l Form a strong expandable support for the anterolatera l abdominal wal l .

l Protect the abdominal viscera f rom injury.

l Compress the abdominal contents to mainta in or increase the intra-abdominal pressure and, in so doing, oppose the

diaphragm ( in creased intra-abdominal pressure fac i l i tates expuls ion).

l Move the trunk and he lp m ainta in posture.

The anterolatera l abdominal musc les protect and support the abdominal v iscera. The obl ique and transverse m usc les ,

act ing together b i latera l ly, form a muscular g ird le that exerts f irm pressure on the abdominal viscera. The rectus

abdominis part ic ipates l i t t le , i f at a l l , in this act ion. Compress ing the abdominal viscera and increas ing intra-abdominal

pressure e levates the re laxed d iaphragm to expel a ir dur ing respirat ion and more forc ib ly for coughing, sneez ing, nose

blowing, voluntary eructat ion (burp ing), and ye l l ing or screaming. W hen the d iaphragm contracts dur ing insp irat ion, th e

anterolatera l abdominal wal l expands as i ts musc les re lax to make room for the organs, such as the l iver , that are pushed

infer ior ly. The combined act ions of the anterolateral m usc les a lso produce the force required for defecat ion (evacuation of

feca l mater ia l f rom the rectum), mictur it ion (ur inat ion), vomit ing, and partur it ion (chi ldb ir th). Increased intra-abdominal

(and intrathorac ic) pressure is a lso involved in heavy l i f t ing, the result ing force sometimes produc ing a hernia.

The anterolatera l abdominal musc les are a l so involved in mov ements of the trunk at the lumbar vertebrae and in

control l ing the t i l t of the pe lvis when standing for maintenance of posture (res is t ing lumbar lordos is) . Consequently,

s trengthening the anterolatera l abdominal wal l m usculature improves standing and s itt ing posture. The rectus abdominis

is a powerful f lexor of the thorac ic reg ion and espec ial ly of the lumbar region of the vertebra l column, pul l ing the anter ior

costa l margin and pubic crest toward each other . The obl ique abdominal musc les a lso ass is t in movem ents of the trunk,

espec ia l ly latera l f lexion and rotat ion of the lumbar and l ower thorac ic vertebra l column. The transverse abdominal musc le

probably has no apprec iable ef fect on the vertebra l column (Wil l iams et a l. , 1995).

Protuberance of the Abdomen

A prominent abdomen is norm al in infants and young chi ldren because the ir gastrointest ina l (GI) tracts conta in

cons iderable amounts of a ir . In addit ion, the ir anterolatera l abdominal cavit ies are enlarg ing and t he ir abdominal musc les

are gaining strength. An infant 's and young chi ld 's re lat ive ly large l iver a lso accounts for s ome bulg ing. Abdominal

musc les protect and support the viscera most e f fect ive ly when they are wel l toned; th us the wel l-condit ioned adult of

normal weight has a f lat or scaphoid ( l i t . boat shaped; i .e . , hol lowed or concave) abdomen when in the supine pos it ion.

The s ix common causes of abdominal protrus ion begin with the letter F :food, f lu id, fat, feces, f latus, and fetus. E vers ion

of the umbil icus may be a s ign of increased intra-abdominal pressure, usual ly result ing f rom asc ites (abnormal

accumulat ion of serous f lu id in the per itoneal cavity) or a large mass (e.g., a tumor, a fetus, or an enlarged organ such

as the l iver) .

Excess fat accumulat ion owing to overnour ishment most comm only involves the subcutaneous fatty layer; however, there

may a lso be excess ive depos it ions of extraper itoneal fat in som e types of obes ity.

Tumors and organomegaly (organ enlargement such as sp lenomegaly, or enlargement of the sp leen) a lso produce

abdominal enlargement. When the anter ior abdomi nal musc les are underdeveloped or become atrophic , as a result of o ld

age or insuf f ic ient exerc ise. They provide i nsuf f ic ient tonus to res is t the increased weight of a protuberant abdomen on

the anter ior pe lvis . The pe lvis t i l ts anter ior ly at the hip jo ints when standing (the pubis descends and the sacrum

ascends) produc ing ex cess ive lordosis of the lumbar region of the vertebra l column (see Chapter 4 for deta i ls).

Abdominal Hernias

The anterolatera l abdominal wal l may be the s ite of hern ia s .Most hernias occur in the inguinal, umbi l ica l, and epigastr ic

regions (see c l in ica l corre lat ion [b lue] box In guinal Hernias , in this chapter) Umbil ica l he rnias are common in

newborns because the anter ior abdominal wal l is re lat ive ly weak in the um bil ical r ing, espec ia l ly in low-bir th-weight

infants . Umbil ica l hernias are usual ly smal l and result f rom increased intra-abdominal pressure in the presence of

weakness and incomplete c losure of the anter ior abdominal wal l a f ter l igat ion of the umbil ica l cord at b ir th. Herniat ion

occurs through the umbil ica l r ing. Ac q ui re d um bi l ic al hern ias occur most commonly in women and obese people.

Extraper itoneal fat and/or per itoneum protrude into the hernia l sac. Th e l ines a long which t he f ibers of the abdominal

aponeuroses inter lace are also potentia l s ites of herniat ion (F ig. 2.5B). Occasionally, gaps exist where these f iber

exchanges occurfor example, in the mid l ine or in the trans it ion f rom aponeuros is to rectus sheath. These gaps may be

congenita l, the result of the s tresses of obes ity and aging, or the consequence of surg ica l or traumatic wou nds. An

ep igastr ic hernia, a hernia in the epigastr ic reg ion through the l inea a lba, occurs in the mid l ine between the xiphoidprocess and the umbilicus. Spigel ian herniasare t hose occurr ing a long the semilunar l ines. These types of hernia tend to

occur in people > 40 years and are usually associated with obesity. The hernial sac, composed of peritoneum, is covered

with only skin and fatty subcutaneous t issue.

The Bottom Line

The anterolatera l abdominal m usc les cons is t of concentr ic , f lat musc les located anterolatera l ly and vert ica l musc les

placed anter ior ly adjacent to the mid l ine. A tr i laminar arrangement of the f lat m usc les , l ike that in the thorax, a lso

occurs here; however, other than the ir innervation by mult ip le but separate segmental nerves, the metamer ism

(segmentat ion) character is t ic of the t horac ic intercosta l musculature is not apparent in t he abdomen. Th e f leshy port ions

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of the f lat musc les become aponeurot ic anter ior ly. The f ibers of the aponeuroses inter lace in t he mid l ine, forming the

linea alba, and continue into the aponeuroses of the contralateral muscles. The aponeurotic f ibers of the external obliques

are a lso continuous across the mid l ine with those of the contra latera l internal ob l ique musc les . Thus t hree layers of f lat,

b i latera l d igastr ic musc les enc irc le the trunk, forming obl ique and transverse g ird les that enc lose the abdominal cavity. In

the upper two thirds of the abdominal wal l , the aponeurot ic layers separate on each s ide of the l inea a lba to form

longitudinal pockets , or sheaths, that conta in the rectus musc les . This br ings them into a funct ional re lat ionship with the

f lat musc les in which the v ert ica l musc les brace the g ird les anter ior ly. In the lower third of the anter ior abdominal wal l ,

the aponeuroses of a l l three layers of f lat musc les pass anterior to the rectus musc les (rect i) . As f lexors of the trunk, the

rect i are the antagonis t ic partners of the deep (extensor) musc les of the back. Balance in t he development and tonus ofthese partners af fects posture (and thus weakness of the abdominal musc les may result in excess ive lumbar lordos is) . The

spec ia l arrangements of the anterolatera l abdominal musc les enable them to provide f l exib le conta ining wal ls for t he

abdominal contents , to increase intra-abdominal pressure or decrease abdominal volume for expuls ion, and to produce

anter ior and latera l f lexion and tors ional (rotatory) movements of the trunk.

N e r v e s o f t h e A n t e r o l a t e r a l A b d o m i n a l W a l l

The map of dermatomes of the anterolatera l abdominal wal l is a l most identica l to the map of per iphera l nerve d is tr ibut ion

(Table 2.3). This is because the anter ior rami of sp inal nerves T7T12, which supply most of the abdominal wal l , do not

part ic ipate in p lexus formation. The exception occurs at the L1 leve l, wh ere the L1 anter ior ramus b ifurcates into two

named per iphera l nerves. Each dermatome begins poster ior ly over lying the intervertebra l foramen by which the sp inal

nerve exits the vertebra l column and fo l lows the s lope of the r ibs around the trunk. D ermatome T10 inc ludes the

umbil icus, whereas dermatome L1 inc ludes the inguinal fo ld.

The skin and m usc les of the anterolatera l abdominal wal l are suppl ied mainly by the fo l lowing nerves (F ig. 2.8A; Table

2.3):

l Thoracoabdominal nerves: the d is ta l, abdominal parts of the anterior rami of the infer ior s ix thorac ic sp inal nerves

(T7T11); these are the former infer ior intercosta l nerves d is ta l to the costa l margin.

l Lateral (thoracic) cutaneous branches: of the thorac ic sp inal nerves T7T9 or T10.

l Subcostal nerve: the large anter ior ramus of sp inal nerve T12.

l Il iohypogastric and i l ioinguinal nerves: terminal branches of the anter ior ramus of sp inal nerve L1.

The th oracoabdominal nerves pass inferoanter ior ly f rom the intercosta l spaces and run in the n eurovascular p lane between

the internal ob l ique and the transverse abdominal musc les to supply the abdominal skin an d musc les . The latera l

cutaneous branches emerge from t he musculature of the anterolatera l wal l to enter the subcutaneous t issue a long the

anter ior axi l lary l ine (as anter ior and poster ior d ivis ions), whereas the anter ior abdominal cutaneous branches p ierce the

rectus sheath to enter the subcutaneous t issue a short d is tance f rom the median p lane. Of the anterior abdomina l

cutaneous branches of thoracoabdomina l nerve(s):

l T7T9supply the skin super ior to the umbil icus.

l T1 0innervates the skin around the umbil icus.

l T1 1, p lus the cutaneous branches of the subcosta l (T12), i l iohypogastr ic , and i l io inguinal (L1), supply the skin

infer ior to the umbil icus.

Dur ing the ir course through the wal l , the thoracoabdominal, subcosta l, and i l iohypogastr ic nerves communicate with each

other.

Palpation of the Anterolateral Abdominal Wall

Warm hands are espec ia l ly important when palpat ing the abdominal w al l because cold hands mak e the anterolatera l

abdominal musc les tense, produc ing involuntary spasms of the musc les , known a s guard ing .Intense guard ing, board- l ike

ref lexive m uscular r ig id ity that cannot be wi l l fu l ly suppressed, occurs dur ing palpat ion when an organ (such as the

appendix) is inf lamed and i n i tse l f const itutes a c l in ica l ly s ignif icant s ign of acute abdomen.The involuntary m uscular

spasms attempt to protect the viscera f rom pressure, which is pa inful when an abdominal infect ion is present. The

common nerve supply of the skin and musc les of the wal l expla ins why these spasms occur. Pa lpat ion of abdominal

viscera is per formed with the patient in the supine pos it ion with thighs and knees semif lexed to enable adequate

re laxation of the anterolatera l abdominal wal l . Otherwise, the deep fasc ia of the thighs pul ls on the membranous layer of

abdominal subcutaneous t issue, tens ing the abdominal wal l . Som e people tend to p lace the ir hands b ehind the ir heads

when lying supine, w hich a lso t ightens the musc les and makes t he examination d if f icult. P lac ing the upper l imbs at the

s ides and putt ing a p i l low under the person's knees tends to re lax the anterolatera l abdominal musc les .

Superficial Abdominal Reflexes

Phys ic ians and sur geons examine the ref lexes of the abdominal wal l to determine i f there is abd ominal d isease, such as

appendic it is . The abdominal wal l is the only protect ion most of the abdominal organs have. Consequently, i t wi l l react i f

an organ i s d iseased or injured. With the person supine and the musc les re laxed, the super f ic ia l abdominal re f lex is

e l ic i ted by quickly s troking hor izonta l ly, latera l to media l, toward the umbil icus. Usual ly, contract ion of the abdominal

musc les is fe lt; this re f lex may not be observed in ob ese people. Similar ly, any injury to the abdominal skin results in a

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rapid ref lex contract ion of the abdominal musc les .

P .207

Table 2.3. Nerves of the Anterolateral Abdominal Wall

Nerv es Origin Co ur se Dist ribution

Thoracoabdominal

(T7T11)

Continuation of

lower (7th11th)

intercosta l nerves

dis ta l to costa l

margin

Run between second and third

layers of abdominal muscles;

branches enter subcutaneous

t issue as latera l cutaneous

branches of T10T11 ( in

anter ior axi l lary l ine) and an ter ior

cutaneous branches of T7T11

(parasternal l ine)

Musc les of ante rolatera l

abdominal wal l and

overlying skin

7th9th latera l

cutaneous branches

7th9th

intercostal nerves(anterior rami of

sp inal nerves

T7T9)

Anter ior d ivis ions continue across

costa l margin in subcutaneoust issue

Skin of r ight and left

hypochondr iac regions

Subcosta l (anter ior

ramus of T12)

S pi nal n er ve T 12 Ru ns a lo ng i nf er io r b or de r of 1 2t h

r ib; then onto subumbil ica l

abdominal wal l b etween second

and third layers of abdominal

musc les

Musc les of ante rolatera l

abdominal wal l ( inc lud ing

most i nfer ior s l ip of

external ob l ique) and

over lying skin, super ior to

i l iac crest and infer ior to

umbil icus

I li oh yp og as tr ic (L 1) A s su pe ri or

terminal branch of

anterior ramus of

sp inal nerve L1

Pierces transverse abdominal

musc le to course between second

and third layers of abdominal

musc les; branches p ierce ex ternalobl ique aponeuroses of most

infer ior abdominal wal l

Skin overlying iliac crest,

upper inguinal, and

hypogastric regions;

internal oblique andtransverse abdominal

musc les

I l io in guinal (L 1) As in ferior

terminal branch of

anterior ramus of

sp inal nerve L1

Passes between second and third

layers of abdominal musc les; then

traverses inguinal canal

Skin of lower inguinal

reg ion, mons pubis , anter ior

scrotum or lab ium majus,

and adjacent media l th igh;





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Injury to Nerves of the Anterolateral Abdominal Wall

The infer ior thorac ic s p inal nerves (T7T12) an d the i l iohypogastr ic and i l io inguinal nerves (L1) approach the abdominal

musculature separate ly to provide the mult i-segmental inne rvation of the abdominal musc les (versus the l imbs, in which

mult i-segmental per iphera l nerves provide innervation). Thus they are d is tr ibuted across the anterolatera l abdominal wal l ,

where they run obl ique but mostly hor izonta l courses and are susceptib le to injury in surg ica l inc is ions or f rom trauma at

any leve l of the abdominal wal l . Injury to them dur ing surgery or f rom an abdominal injury m ay result in weakening of the

musc les . In the inguinal reg ion, such a weakness may predispose an ind ividual to deve lopment of an inguinal hernia (see

c l in ica l corre lat ion [b lue] box Inguinal Hernias , in this chapter) .

Abdominal Surgical Incisions

Surgeons use v ar ious inc is ions to gain access to the abdominal cavity. When poss ib le , the inc is ions fo l low the c leavage

l ines (Langer l ines) in t he skin (see Introduct ion for d iscuss ion of these l ines). The inc is ion that a l lows adequate exposure

and, secondar i ly, the best poss ib le cosmetic e f fect, is chosen. The locat ion of the inc is ion a lso depends on the type of

operat ion, the l ocat ion of the organ(s) the surgeon wants to reach, bony or cart i lag inous boundar ies , avoidance of

(espec ia l ly motor) nerves, maintenance of b lood supply, and minimiz ing injury to musc les and fasc ia of the wal l whi le

a iming for favorable heal ing. Thus before making an inc is ion, the surgeon cons iders the d irect ion of the musc le f ibers and

the locat ion of the aponeuroses and nerves. Consequently, a var iety of i nc is ions are routine ly used, each having spec if ic

advantages and l imitat ions.

Instead of transect ing musc les , caus ing ir revers ib le necros is (death) of musc le f ibers , the surgeon sp l i ts them in the

direct ion of (and b etween) the ir f ibers . The rectus abdominis is an exception; i t can be transected because its musc le

f ibers run short d is tances between tendinous intersect ions and its segmental innervation enters at t he latera l part of the

rectus sheath. Th erefore, the nerves can be eas i ly located and preserved. The surgeon chooses the part of t he

anterolatera l abdominal wal l t hat g ives the f reest access to the targeted organ with the least d is turbance to the nerve

supply to the musc les . Musc les and viscera are retracted toward, not away f rom, the ir neurovascular supply. Cutt ing a

motor nerve para lyzes the musc le f ibers suppl ied by it , thereby weakening the anterolatera l abdominal wal l . However,

because of over lapping areas of innervation between nerves, one or two smal l branches of nerves may usual ly be cut

without a not iceable loss of motor supply to the musc les or loss of sensation to t he skin. L itt le i f any communicat ion

occurs between nerves f rom the lateral border of the rectus abdominis to the anter ior mid l ine.

Longitudinal Incisions

Longitud ina l incis ionsare used centra l ly in the abdomen, because musc le and vasculature are pr imar i ly longitudinal ly

or iented here and the n erves, which have been approaching c ircumferentia l ly or transverse ly, d iminish in s ize and

s ignif icance near the m id l ine. Longitudinal inc is ions, such as median and paramedian inc is ions (F ig. B2 .1), are preferred

for exploratory operat ions b ecause they of fer good ex posure of and access to the viscera and can be extended as

necessary with minimal complicat ion.

Med iano r midl ine incis ions can be made rapid ly without cutt ing m usc le, major b lood vesse ls , or nerves. They cut through

the f ibrous t issue of the l inea a lba, super ior and/or infer ior to the umbil icus. Because the l inea a lba transmits only smal l

vesse ls and nerves t o the skin, a mid l ine inc is ion is re lat ive ly b loodless and avoids major nerves; however, inc is ions in

some people may reveal abundant and wel l-vascular ized fat, part icular ly in the fa lc i form l igament of the l iver (d iscussed

later in this chapter) . Converse ly, because of i ts re lat ive ly poor b lood supply, the l inea a lba may undergo necros is and

subsequent degenerat ion af ter inc is ion i f i ts edges are not a l igned proper ly dur ing c losure. Median inc is ions can be m ade

along any part or t he length of the l inea a lba f rom the xiphoid process to pubic symphys is . Lower median inc is ions (be low

the umbil icus) are f requently used for reaching fem ale pe lvic viscera.

inferiormost internal

obl ique and transverse

abdominal





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Paramedian incis ions ( latera l, le f t or r ight, to the median p lane) are made in the sagitta l p lane and may extend f rom t he

costa l margin to the pubic hair l ine. Af ter the inc is ion passes through the anter ior layer of the rectus sheath, the musc le is

f reed and retracted latera l ly to prevent tens ion and injury t o the vesse ls and nerves. The poster ior layer of the rectus

sheath and the per itoneum are then inc ised to enter the per itoneal cavity.

Oblique and Transverse Incisions

Ob l iqueand transverse incis ions are used most commonly on one s ide of the mid l ine and espec ia l ly i n the more per ipheral

abdomen wh ere the ir d irect ion is re lated to m usc le f iber or ientat ion, nearby hard t issue (costa l margin or i l iac or pubiccrest) , or minimiz ing potentia l nerve damage.

Grid iron ( muscle-sp l i t t ing) incis ions are of ten used for an appendectomy. The obl i que McBurney incis ion is made at the

McBurney po in t , approximate ly 2.5 cm superomedia l to the ASIS on t he sp inoumbi l ica l l ine. This inc is ion is currently less

popular than an a lmost transverse inc is ion in the l ine of a skin crease. In either case, the external ob l ique aponeuros is is

inc ised inferomedia l ly in the d irect ion of i ts f ibers and retracted. The musculoaponeurot ic f ibers of the internal ob l ique

and transverse abdominal are then sp l i t in the l ine of the ir f ibers and retracted. The i l iohypogastr ic nerve, running deep

to t he internal ob l ique, is identi f ied an d preserved. Careful ly made, the entire exposure cuts no musculoaponeurot ic

f ibers; therefore, when the inc ision is c losed, the musc le f ibers move together and the abdominal wal l is as s trong af ter

the operat ion as i t was before. W hen kept re lat ive ly smal l and done careful ly, the gr id iron inc is ion provides good access

and avoids cutt ing, tear ing, and stretching of nerves.

Suprapub ic(Pfannenst iel ) i n c i s ions(bikini inc is ions) are made at the p ubic hair l ine. These inc is ionshor izonta l

with a s l ight c onvexityare used for most gynecologica l and obstetr ica l operat ions (e.g., for cesarean sect ion and

removal of a tubal pregnancy). The l inea a lba and the anter ior layers of t he rectus sheaths are transected and resected

super ior ly, and the rectus m usc les are retracted latera l ly or d ivided through t he ir tendinous parts a l lowing reattachment

without musc le f iber injury. Th e i l iohypogastr ic and i l io inguinal nerves are identi f ied and preserved.

Transverse incis ionsthrough t he anter ior layer of the rectus sheath and rectus abdominis provide good access and cause

the least poss ib le damage to the nerve supply of the rectus abdominis . This musc le m ay be d ivided transverse ly without

ser ious damage because a new transverse band forms that, when the musc le segments are re joined, is s imi lar to a

tendinous intersect ion. Transverse inc is ions are not made through the tendinous intersect ions because cutaneous nerves

and branches of the super ior ep igastr ic vesse ls p ierce these f ibrous regions of the m usc le. Transverse inc is ions are m ost

useful above the leve l of the umbil icus. They can be increased lateral ly as needed to increase exposure but are not good

for exploratory procedures because super ior and infer ior extens ion is d i f f icult.

Subcosta l incis ionsprovide access to t he gal lb ladder and b i l iary ducts on the r ight s ide and the sp leen on t he le f t. The

inc is ion is made para l le l but at least 2.5 cm infer ior to the costa l margin to avoid the 7th and 8th thorac ic sp inal nerves

(Table 2.3).

Figure B2.1.





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High-Risk Incisions

High-risk incis ionsinc lude pararectus and in guinal inc is ions. Pararectus incis ions along the lateral border of the rectus

sheath are undes irable because they are l ike ly to cut the nerve supply to the rectus abdominis . Blood supply f rom the

infer ior ep igastr ic ar tery a lso may be compromised. Inguina l incis ionsfor repair ing hernias m ay injure the i l io inguinal

nerve directly or it may be inadvertently included in the suture during closure of the incision. In such cases, people may

fee l pa in in the L1 dermatome region, which inc ludes the scrotum (or the lab ium majus).

Incisional Hernia

A n incis iona l hernia is a protrusion of omentum(a fo ld of per itoneum) or an organ through a surg ica l inc is ion. Surgeons

who mak e inc is ions based on a thorough knowledge of anterolatera l abdominal wal l an atomy wi l l only occas ional ly have todeal with this problem. However, i f th e muscular and aponeurot ic layers of the abdomen do not heal proper ly, an

inc is ional hernia can result. F actors predispos ing a pat ient to inc is ional hernia inc lude advanced age or debi l i ty of the

patient, obes ity, and postoperat ive wound i nfect ion.

Minimally Invasive (Endoscopic) Surgery

Many abd ominopelvic surg ica l pr ocedures are now per formed u s ing an endoscope , in which t iny per forat ions of the

abdominal wal l a l low the entry of remote ly operated instruments, rep lac ing the larger conventional inc is ions. Thus the

potentia l for nerve injury, inc is ional hernia, or contamination through the open wou nd and the t ime required for heal ing

are minimized.

The Bottom Line

The anterolatera l abdominal m usc les rece ive mult i-segmental innervation via the anter ior rami of lower thorac ic

(T7T12) and the L1 sp inal nerves. The rami p ass separately to the musc les ( i .e . , without unit ing into m ult i-segmental

per iphera l nerves as occurs in t he l imbs) as f ive t horacoabdominal nerves (T7T11), a subcosta l nerve (T12), and

i l iohypogastr ic and i l io inguinal nerves (L1) that course in a p lane between the second and third layers . Latera l cutaneous

branches supply the ove r lying abdominal skin latera l to the MCL; anter ior cutaneous branches supply skin media l t o the

MCL. Except for L1, the maps of the abdominal dermatomes and of t he per iphera l nerves are thus identical. Landmark

dermatomes are dermatome T10, which inc ludes the umbil icus, and dermatome L1, which inc ludes the inguinal fo ld.

V e s s e l s o f t h e A n t e r o l a t e r a l A b d o m i n a l W a l l

The skin and subcutaneous t issue of the abdominal wal l is served by an intr icate subcutaneous venous p lexus, dra ining

superior ly to the internal thorac ic ve in media l ly and t he latera l thorac ic ve in latera lly and infer ior ly to the super f ic ia l and

infer ior ep igastr ic ve ins, tr ibutar ies of the femoral and ex ternal i l iac ve ins, respect ive ly (F ig. 2.9). Cutaneous ve ins

surrounding the umbil icus anastomose with parumbil ical veins , smal l tr ibutar ies of the po rt al ve in that parallel the

obliterated umbil ical vein ( round l igament of the l iver) . A re lat ive ly d irect latera l super f ic ia l anastomotic channel, the

thoracoepigastric vein, may exis t or deve lop (as a result of a ltered venous f low) between the superf ic ia l ep igastr ic vein

(a femoral ve in tr ibutary) and the la tera l thoracic vein(an axi l lary ve in tr ibutary). The deeper ve ins of the anterolatera l

abdominal wal l accompany the arter ies , bear ing the same name. A deeper, media l venous anastomos is m ay exis t or

develop between the in ferior ep igastr ic vein (an external il iac vein tr ibutary) and the superior ep igastr ic/ interna l thoracic

ve ins (subc lavian ve in tr ibutar ies). The super f ic ia l and deep anastomoses may af ford col latera l c irculat ion dur ing b lockage

of e ither vena cava.

The pr imary b lood vesse ls (ar ter ies and ve ins) of the anterolatera l abdominal wal l are the

l Superior ep igastr ic vessels and branches of the musculophrenic vessels from the internal thoracic vessels.

l Inferior ep igastr icand deep circumflex i l iac vesselsf rom the external i l iac vesse ls .

l Superf ic ia l c ircumflex i l iac and superf ic ia l ep igastr ic vessels f rom the femoral ar tery and greater saphenous ve in,

respect ive ly.

l Posterior intercosta l vessels of the 11th intercostal space and the anterior branches of subcosta l vessels

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The arter ia l supply to the anterolatera l abdominal wal l is summar ized in Table 2.4. The d is tr ibut ion of the deep abdominal

b lood vesse ls re f lects the arrangement of the musc les: The vessels of the anterolatera l abdominal wal l have an obl ique,

circumferential pattern (similar to the intercostal vessels above), whereas the vessels of the central anterior abdominal

wal l are or iented m ore vert ica l ly.

The superior epigastric artery is the d irect continuation of the interna l thoracic artery.It enters th e rectus sheath

super ior ly through its poster ior layer and s uppl ies the super ior part of the rectus abdominis and anastomoses with the

infer ior ep igastr ic artery approximate ly in the umbil ica l reg ion (F ig. 2.8, Table 2.4)

The inferior epigastric artery arises from the externa l i l iac arteryjust super ior to the inguinal l igament. It runs

super ior ly in the transversal is fasc ia to enter the rectus sheath be low the arcuate l ine. It enters the lower rectus

abdominis and anastomoses with the super ior ep igastr ic ar tery.

Figure 2.9. Lymphatics and superficial veins of anterolateral abdominal wall . Most super f ic ia l lymphatic

vesse ls super ior to the umbil icus dra in to the axi l lary lymph nodes; a few dra in media l ly and deeply to the

parasternal and anter ior d iaphragmatic lym ph nodes. Su per f ic ia l lymphatic vessels infer ior to the umbil icus d ra in to

the super f ic ia l inguinal lymph nodes. The pattern of super f ic ia l venous dra inage is more vert ica l than transverse

(c ircumferentia l) . The thoracoepigastr ic ve in, formed of anastomos ing tr ibutar ies of the latera l thorac ic (axi l lary) and

superf ic ia l ep igastr ic ( femoral) ve ins, is capable of provid ing col latera l c irculat ion between the super ior a nd the

infer ior vena caval syst ems.

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Table 2.4. Arteries of the Anterolateral Abdominal Wall





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Artery Or ig in Co urse Dis tribu tion

Musculophrenic

Internal

thorac ic

artery

De sce nds al on g c os ta l m ar gin S up erf ic ial a nd de ep ab do min al

wal l of hypochondr iac region;

anterolatera l d iaphragm

Superior ep igast r ic Descends in rec tu s sheath deep to

rectus abdominis

Rectus abdominis musc le;

super f ic ia l and deep abdominal

wal l of ep igastr ic and upper

umbil ica l reg ions

10th and 11th

poster ior intercosta lar ter ies Aor ta

Arteries continue beyond ribs to

descend in abdominal wal l betweeninternal ob l ique and transverse

abdominal mu sc les

Superf ic ial and deep abdominal

wal l of latera l ( lumbar or f lank)region

Subcosta l ar tery

Infer ior ep igastr ic

External

i l iac ar tery

Runs super ior ly and enters r ectus

sheath; runs deep to rectus

abdominis

Rectus abdominis musc le; deep

abdominal wal l of pubic and

infer ior umbil ica l reg ions

Deep ci rcumflex i li ac Runs on deep aspect of an ter ior

abdominal wal l , para l le l to inguinal

l igament

Il iacus musc le and deep

abdominal wal l of i nguinal

reg ion; i l iac fossa

Superf ic ia l

circumflex il iac

Femoral

artery

Runs in subcutaneous t issue a long

inguinal l igament

Superf ic ial abdominal wal l of

inguinal reg ion and adjacent

anter ior thigh

Superf i cia l epigastr ic Runs in subcu taneous ti ssue toward

umbil icus

Superf ic ial abdominal wal l of

pubic and infer ior umbil ica l

reg ion

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Lymphatic dra inage of the anterolatera l abdominal wal l fo l lows the fo l lowing patterns (F ig. 2.9):

l Superf ic ia l lymphat ic vesselsaccompany the subcutaneous ve ins; those super ior to th e transumbil ica l p lane dra in

mainly to t he axil lary lymph nodes; however, a few drain to the parasternal lymph nodes.Super f ic ia l l ymphatic

vesse ls infer ior to the transumbil ica l p lane dra in to the superficial inguinal lymph nodes.

l Deep lymphat ic vesselsaccompany the deep ve ins of the abdominal wal l and dra in to the external i l iac, common

i l iac, and r igh t and left lumbar( cava land aort ic) lymph nodes.

For an overv iew of super f ic ia l and deep lymphatic dra inage, see the Int roduct ion.

Reversal of Venous Flow and Collateral Pathways of Superficial Abdominal Veins

When f low in the super ior or infer ior vena cava is obstructed, anastomoses between the tr ibutar ies of these systemic

ve ins, such as the thoracoepigastr ic ve in, may provide col latera l pathways by which the obstruct ion may be bypassed,

a l lowing b lood to return to the heart (F ig. B2.2). Smal l cutaneous (systemic) ve ins surrounding the umbil icus a lso

anastomose with the paraumbil ica l ve ins (tr ibutar ies of the porta l ve in), which run with the obl i terated umbil ica l ve in

(round l igament of t he l iver) . Dur ing e ither caval or porta l obstruct ion, these anastomos ing ve ins may a lso become

distended, caus ing the caput medusaeappearance (referr ing to the head of Medusa, who had wr ithing snakes for hair) .

The Bottom Line

The skin an d subcutaneous t issue of the abdominal wal l dra in super ior ly (ult imate ly to the super ior vena caval system)

via the internal thorac ic v ein media l ly and the latera l thorac ic ve in latera l ly, and infer ior ly (ult imate ly to the infer ior vena

caval system) via t he super f ic ia l and infer ior ep igastr ic ve ins. Cutaneous ve ins surrounding the umbil icus anastomose

with smal l t r ibutar ies of the porta l ve in. Th e d is tr ibut ion of the deeper abdominal b lood vessels re f lects the arrangement

of the musc les: an obl ique, c ircumferentia l pattern (s imi lar to the intercosta l vessels above) over the ant erolatera l

abdominal wal l and a vert ica l pattern anter ior ly. The c ircumferentia l vessels of the anterolatera l wal l are continuations of

the 11th poster ior intercostal vesse ls , subcosta l vesse ls , an d deep c ircumf lex i l iac vesse ls . An a nastomos is between the

super ior and the infer ior ep igastr ic vesse ls within the rectus sheath inc ludes the vert ica l vesse ls . A super f ic ia l

anastomotic channel, the thoracoepigastr ic ve in, and the deeper media l pathway between the infer ior and th e super ior

epigastric veins afford collateral circulation during blockage of either vena cava.

Superf ic ia l abdominal lymphati c vesse ls super ior to the transumbil ica l p lane dra in pr imar i ly to the axi l lary lymph nodes;

those infer ior to the p lane dra in to the super f ic ia l inguinal lymph nodes. Deep lymphatic vesse ls accompany deep ve ins of

the abdominal wal l to the i l iac and r ight and le ft lumbar (caval and aort ic) lymph nodes.

I n t e r n a l Su r f a c e o f t h e A n t e r o l a t e r a l A b d o m i n a l W a l l

The internal (poster ior) sur face of the anterolatera l abdominal wal l is covered with transversal is fasc ia, a var iab le am ount

of extraper itoneal fat, and par ietal per itoneum (F ig. 2.10). The inf raumbil ica l part of this sur face exhib its severa l

peritoneal folds, some of which contain remnants of vessels that carried blood to and from the fetus (Moore and Persaud,

2003). F ive umbi l ica l peri tonea l fo ldstwo on each s ide and one in t he median p lanepass toward the umbil icus:

Figure B2.2.

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l The median umbil ical fold extends f rom the apex of the ur inary b ladder to the umbil icus and covers the median

umbi l ica l l igament, the remnant of the urachus , which jo ined the apex of the feta l b ladder to the umb il icus.

l Two medial umbil ical folds , latera l to the median umbil ica l fo ld, cover the medial umbil ical l igaments, formed

by occluded parts of the umbi l ica l arteries.

l Two lateral umbil ical folds , latera l to the media l um bi l ica l fo lds , cover the in ferior ep igastr ic vessels and t herefore

bleed i f cut.

The depress ions latera l to the umbil ica l fo lds are the pe ri to neal fo ss ae , each of which is a potentia l s ite for a hernia. The

locat ion of a hernia in one of these fossae determines how the hernia is c lass i f ied. The shal low fossae between the

umbil ica l fo lds are the:

l Supravesical fossaebetween the m edian and the media l umbi l ica l fo lds , formed as the per itoneum ref lects f rom

the anter ior abdomi nal wal l onto the b ladder. The leve l of the supraves ica l fossae r ises and fa l ls with f i l l ing and

emptying of the b ladder.

l Medial inguinal fossaebetween the media l and the latera l umbi l ica l fo lds , areas a lso com monly ca l led inguinal

triangles (Hesselbach triangles) , which are potentia l s ites for the less com mon direct inguinal hernias .

l Lateral inguinal fossae, latera l to the latera l umbi l ica l fo lds , inc lude the deep inguina l r ings and are potentia l s ites

for the mos t common type of hernia i n the lower abdominal wal l , the ind irect inguina l hernia(see c l in ica l corre lat ion

[b lue] box Inguinal Hernias , in this chapter) .

The supraumbil ica l part of the internal sur face of the anter ior abdominal wal l has a sagitta l ly or iented per itoneal

ref lection, the falciform l igament , that extends between the super ior anter ior abdominal wal l and the l iver . It enc loses

the round l igament of the l iver (L. l igamentum teres hepat is) and paraumbilical veins in its inferior free edge. The

round l igament is a f ibrous remnant of the umbil ica l ve in, which extended f rom the umbil icus to the l iver prenata l ly

(Moore and Persaud, 2003).

External Supravesical HerniaAn externa l supravesica l hernialeaves the per itoneal cavity through the supraves ica l fossa. The s ite of this hernia is

media l to that of a d irect inguinal hernia (see c l in ica l corre lat ion [b lue] box Inguinal Hernias , in t his chapter) . The

i l iohypogastr ic nerve is in danger of injury dur ing the repair of this rare type of hernia.

Postnatal Patency of the Umbilical Vein

Before the b ir th of a fetus, the um bil ica l ve in carr ies wel l-oxygenated, nutr ient-r ich b lood f rom t he p lacenta to the fetus.

Although reference is of ten made to the occ luded umbil ica l ve in forming the round l igament of the l iver , this ve in

is patent for some time after birth and is used for umbi l ica l vein catheterizat ionfor ex change transfus ion dur ing ear ly

infancyfor example, in infants with erythrob lastosis feta l is o r hemolyt ic d isease of the newborn (Behrman et al.,

Figure 2.10. Posterior aspect of anterolateral abdominal wall of a male. The peritoneal ligaments, folds, and

fossae are the m ain features of this aspect.

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2000) .

The Bottom Line

The pr imary features of t he internal sur face of the anterolatera l abdominal wal l are per itoneal fo lds over lying structures

radiat ing f rom the um bil ica l r ing and the per itoneal fossae formed in re lat ion to the fo lds . Of the umbil ica l per itoneal

fo lds , the centra l three (m edian and m edia l umbi l ica l fo lds) cover remnants of embryologica l s tructures, whereas the

lateral umbi l ica l fo lds cover the infer ior ep igastr ic vesse ls , making them the most s ignif icant of the fo lds postnata l ly. Th e

per itoneal fossae formed in re lat ion to them inc lude the trans it ional supraves ical fossae, the he ight of which changes with

bladder f i l l ing, and the media l and latera l inguinal fossa, over lying potentia l weak areas in the anter ior abdominal wal lwhere d irect and ind irect inguinal hernias , respect ively, m ay occur. The supraumbil ical fa lc i form l igament enc loses the

remnant of the embryologica l umbi l ica l ve in and the accompanying paraumbil ica l ve ins (tr ibutar ies of the porta l ve in) in

its f ree edge.

I n g u i n a l R e g i o n

The inguinal region(groin), extending between the ASIS and pubic tuberc le , is an important area anatomical ly and

clinically; anatomically because it is a region where structures exit and enter the abdominal cavity and clinically because

the pathways of exit and entrance are potentia l s ites of herniat ion. In fact, the major ity of abdomi nal hernias occur in this

region, with inguinal hernias in part icular accounting for 75% of a l l abdominal hernias . These hernias occur in both sexes,

but most ing uinal hernias (approximate ly 86% ) occur in males because of the passage of the spermatic cord through the

inguina l cana l.

Although the test is is located in the per ineum postnata l ly, the male gonad or ig ina l ly forms in the abdomen. Its migrat ion

out of t he abdomen into the per ineum through the inguinal canal accounts for m any of the structura l features of the

region. Tradit ional ly, the test is a nd scrotum are d issected and studied i n re lat ion to the anter ior abdominal wal l , and the

inguinal reg ion in part icular , in sp ite of the ir postnata l per ineal locat ion.

For these r

Clinically Oriented Anatomy, 5th Edition - 2. Abdomen

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