The lateral nasal wall SB anatomy.pdf

8/10/2019 The lateral nasal wall SB anatomy.pdf

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The lateral nasal wall

I N FER I OR M EATUS

The inferior meatus is that part of the lateral wall of the nose lateral to the inferior turbinate.

It is the largest meatus, extending almost the entire length of the nasal cavity. The meatus is highestat the junction of the anterior and middle third. In adults, this ranges from 1.6 to 2.3 cm ( mean 1

.9 cm) at 1.6 cm along the bony lateral wall. The nasolacrimal duct opens into the inferior meatususually just anterior to its highest point. There is no true valve, the opening being covered by small

folds of mucosa. It can be endoscopically identified in life by gentle massage of the lacrimal sacat the medial canthus.

INFER I O R TU RBI NATE

This structure is composed of a separate bone, the inferior concha which has an irregularsurface, perforated and grooved by vascular channels to which the mucoperiosteum is firmly

attached (Figures 104.26 and 1 04.27) . The bone has a maxillary process which articulates with

the inferior margin of the maxillary hiatus. It also articulates with the ethmoid, palatine and

lacrimal bones, completing the medial wall of the nasolacrimal duct. The inferior concha has itsown ossification centre which appears around the fifth intrauterine month. The turbinatepossesses

an impressive submucosal cavernous plexus with large sinusoids under autonomic control whichprovides the major contribution to nasal resistance. The turbinate is covered by respiratoryepithelium, with a high number of goblet cells (approximately 8/mm2 ) which decrease in density

towards the posterior end.

M IDDLE M EATUS

The middle meatus is that portion of the lateral nasal wall lying lateral to the middleturbinate (Figures 104.28 and104.29 ) . It receives drainage from the frontal, maxillaryand anterior

ethmoidal sinuses. Considerable confusion has arisen with regard to terminology in this area, as

many terms originally defined in the last century by the German and French have been used

interchangeably. In the past, when radical sinus surgery was predominantly used for mostpathology, this was of less significance. The advent of endoscopic smgery has led to an increased

interest in the detailed anatomy of the region and a need for consensus in terminology. Theconfiguration of the structures of the middle meatus are complex and variable, but can more readilybe understood when the embryological development of the area is considered. If the topographical

anatomy is considered in the sagittal plane, a number of structures are apparent, covered by the

middle turbinate. In a disarticulated skull, the maxillary bone has a large opening in its medialwall, the maxillary hiatus. In the articulated skull this is filled in by adjacent bones:

inferior: the maxillary process of the inferior turbinate bone;

posterior: the perpendicular plate of the pala tine bone;

anterosuperior: a small portion of the lacrimal bone;

superior: the uncinate process and bulla of the ethmoid.

A portion of the maxillary hiatus is nevertheless left open by these osseous attachments,

which in life is filled by the mucous membrane of the middle meatus, the mucous membrane ofthe maxillary sinus and the intervening connective tissue - the membranous portion of the lateral

wall. This membranous area can be defined as lying anterior or posterior to the uncinate process,

constituting the anterior and posterior fontanelles, respectively. It is in the fontanelles that

accessory ostia are found, their formation probably arising as a consequence of infection and,consequently, they have been compared to perforations in the tympanic membrane. It is difficult

to ascertain a 'natural' incidence for accessory ostia but it is probably of the order of 4-5 percent in

the general adult population, increasing to 25 percent in patients with chronic rhinosinusitis.


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Accessory ostia are found most frequently in the posterior fontanelle which is generally larger than

its anterior counterpart.

ETH M O I DAL I I\l FU I\l D I B U L U MThe ethmoidal infundibulum is a cleft-like, three dimensional space in the lateral wall of

the nose that belongs to the anterior ethmoid. The medial wall of the space is provided by the entire

extent of the uncinate process and its mucosal covering. The major part of the lateral wall of theethmoidal infundibulum is provided by the lamina papyracea of the orbit, with the frontal processof the maxilla and, in rare cases, the lacrimal bone providing the remainder anterior and superiorly.

Anteriorly, the uncinated process attaches to the bones of the lateral nasal wall at a sharp angle

and inferiorly, provides the bony connection with the inferior turbinate. Bony defects in this areaare covered by connective tissue and the continuation of the periosteum as well as mucous

membrane, and are thus closed in the area of the anterior nasal fontanelle. Through the attachment

of the anterior margin of the uncinate process to the lateral nasal wall, the ethmoidal infundibulum

ends blindly anteriorly in an acute angle. Further inferiorly and posteriorly, the lateral wall of theethmoidal infundibulum is formed by the mucosa-covered connective tissue components of the

posterior nasal fontanelle. The posterior border of the ethmoidal infundibulum is composed largely

of the anterior surface of the ethmoidal bulla, in front of which the infundibulum opens into themiddle meatus through the inferior hiatus semilunaris.

Superiorly, configuration of the ethmoidal infundibulum depends largely on the uncinate

process: if this turns laterally thus attaching to the orbit, the ethmoidal infundibulum ends in a

superior blind alley, the terminal recess (recessus terminalis) . If the uncinate process reaches theskull base superiorly or turns medially to attach to the middle turbinate, the ethmoidal

infundibulum is contiguous with the frontal recess superiorly (Figure 1 04.30) . In these situations,

portions of the lacrimal bone may contribute to the lateral wall of theethmoidal infundibulum.

If a terminal recess of the ethmoidal infundibulum is present, the ethmoidal infundibulum

and frontal recess are separated from each other in this region. The frontal recess then opens in!o

the middle meatus medial to the ethmoidal infundibulum between the uncinate process and themiddle turbinate. Ventilation and drainage of the frontal sinus then run medial to the ethmoidal

infundibulum. If the uncinate process reaches the skull base or turns medially, the frontal recess

and consequently the frontal sinus open directly into the superior part of the ethmoidalinfundibulum. Numerous configurations of these principal uncinate variants can occur. The

superior bony end of the process may become divided into several branches that insert into the

base of the skull, the lamina papyracea and the middle turbinate. Depending on the developmentof these branches, various septations and recesses may be formed. The mucosal membrane may

produce partial or complete septations and form additional blind bulges near the skull base or the

middle turbinate. These can expand anteriorly in varying numbers and sizes and evolve into so-

called infundibular cells. If such a cell develops anteriorly and superiorly, it can extend as far asthe lacrimal bone and may be called an ethmolacrimal cell. No universally accepted terminology

and nomenclature exist in this regard as of today. Posteriorly, the ethmoidal infundibulum tapers

parallel to the tapering of the uncinate process. Depending on the form of the uncinate process, the

anterior length of the ethmoidal infundibulum may reach 4-5 cm. Its greatest depth (measured fromthe free posterior margin of the uncinate process) may be as much as 12 mm, and its greatest width

from the free margin of the uncinated process to lamina papyracea) 5-6 mm. The maxillary sinus

ostium is located in the medial wall of the ethmoidal infundibulum, at the transition of its middleto posterior third.


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The ethmoidal infundibulum may be almost atelectatic, when anatomic variations such as

a paradoxically curved middle turbinate, concha bullosa or hypoplastic maxillary sinus are present.

Occasionally, the uncinated process may be pneumatized, i.e. an ethmoid air cell has developedinto the structure.

Kaufmann has coined the term 'doubled middle turbinate' for an uncinate process, which is

bent medially like the brim of a hat and thus may protrude significantly out of the middle meatus,giving the aspect of an additional middle turbinate. This is interpreted by some as the closest theuncinate process can get to its primary determination, to form an ethmo-turbinal.

CLEFTS A N D SPACES OF TH E LATERAL NASAL WALLThe mucosal lining of the primary nasal cavity and the paranasal sinuses not only serves a

physiological function but also contributes to the shape of these areas. It is only after they are

covered by mucous membrane that the spaces and clefts of the lateral nasal wall assume their

definitive shape and relationship to each other. Thus, the nasal fontanelles become membranous-mucosal components of the lateral nasal wall only after the maxillary sinus and the nasal passages

are covered by mucosa; and the natural ostium of the maxillary sinus assumes its definitive form

only after it is lined by mucosa.

H IATUS SEM I LU NARIS

The term 'hiatus semilunaris' (inferior hiatus semilunaris according to Grunwald) was

coined who gave this name to both the cleft and the depression that are seen from a medial viewlying between the free posterior margin of the uncinate process and the anterior surface of the

ethmoidal bulla; The sickle-shaped hiatus semilunaris can be considered a strictly two-dimensional

formation, i.e. the sagittal cleft between the concave free posterior border of the uncinate processand the convex anterior surface of the ethmoidal bulla. From the middle meatus, through this 'two-

dimensional' cleft, the three-dimensional space of the ethmoidal infundibulum can be approached.

The hiatus semilunaris thus is the 'door' through which we can reach the ethmoidal infundibulum.

Grunwald described a second hiatus semilunaris, the superior hiatus semilunaris. This cleftbetween the ethmoidal bulla and the middle nasal meatus exists, when there is a marked recess

posterior to the ethmoidal bulla, i.e. between this and the frontal portion of the basal lamella of the

middle turbinate. The hiatus semilunaris superior is also a 'sickle-shaped' cleft, which leads intothe retrobullar recess (Figure 104.31 ) .

TH E AGG ER NASIThis area has caused considerable confusion but constitutes, together with the uncinate

process, the remnants of the nasoturbinal in lower mammals and is the most anterior part of the

ethmoid. It is represented by a small crest or mound on the lateral wall just anterior to the

attachment of the middle turbinate. It may be pneumatized, though the incidence in the normalpopulation is considered to be between 5 and 80 percent. Pneumatization of the agger nasi region

may encroach upon the nasolacrimal duct.

THE FRONTAL RECESSThe frontal recess is found in the most anterosuperior portion of the middle meatus. The

term 'frontonasal duct' has been generally abandoned as no true duct exists, either histologically or

topographically, in most people. The natural ostium of the frontal sinus is somewhat variable in itsconfiguration but most frequently it presents as an hourglass narrowing opening directly into the


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recess. Rarely, a longer narrowed region is found. In 10 percent of patients, multiple ostia are

found, though these openings should not be confused with a more laterally placed suprabullar

(superior anterior ethmoidal) cell running into the orbital roof.The frontal recess may be defined as follows:

medial: middle turbinate;

lateral: lamina papyracea, lacrimal bone; superior: skull base;

inferior: dependent upon the attachment of the uncinate process;

pneumatization of agger nasi cells.

From a developmental point of view, this space is the superior continuation of the ascending branchof the first primary interturbinal furrow, i.e. the groove between the first and second ethmoturbinal

crests. The descending branch of this first groove becomes the ethmoidal infundibulum, thus

indicating the close topographic relationship between these two spaces. The frontal sinus originates

from pneumatization of the frontal recess in an antero-superior direction, into the frontal bone. Ina sagittal section through the transition of the floor of the frontal sinus (frontal sinus infundibulum)

to the frontal recess, an hourglass-shaped structure is present. Its narrowest part is at the level of

the frontal ostium. Whereas the superior portio n of the hourglass is the frontal sinus infundibulum,the inferior portion (the 'inverted funnel' ) is the frontal recess. The limits, shape and width of the

latter are largely determined by its neighbouring structures. The posterior wall of the frontal recess

is only well defined if the bulla lamella ascends in continuity to the roof of the ethmoid. The ground

lamella of the bulla then separates the frontal recess from the suprabullar recess. As the ethmoidalbulla lamella is frequently inco mplete and does not reach the roof of the ethmoid over the entire

width of the latter, the frontal recess may communicate widely posteriorly with the space above

(and occasionally behind) the ethmoidal bulla, namely, supra- and retrobullar recess. The shape ofthe ethmoidal bulla can significantly affect the configuration of the frontal recess: if it extends far

forward in the case of a well-developed bulla, the frontal recess will be narrowed from posteriorly.

If, in addition, significant pneumatization of the agger nasi exist and additional ethmoidal

infundibular ceils, the frontal recess may be narrowed to a small passage or even have a tubularlumen. It is this configuration that probably gave rise to the term 'nasofrontal duct'. Even if such a

tubular configuration is present, this is not an independent bony tubular structure but simply the

space wruch other independent bony structures leave between them..The anatomic situation can be further complicated in that the most anterior ethmoidal cells

may develop from the frontal recess. Thus, pneumatization of the- agger nasi may begin here. The

middle turbinate may also become pneumatized from the frontal recess. From here, cells notuncommonly develop into the frontal bone, alongside the frontal sinus proper. These cells have

been called bulla frontalis This variation may range from a bare suggestion of a bulge of the frontal

recess into the floor of the frontal sin us to the format;ion of two or more approximately equally

large cells on one side of the frontal bone. As all of these cells open into the frontal recess, it maybecome impossible in some cases to determine which of those cells is the true frontal sinus and

which a bulla frontalis.

TH E ETH M O I DAL B U LLAThis is one of the most constant features in the middle meatus containing the largest

anterior ethmoidal cell, but it may be poorly aerated or completely unpneu matized in 8 percent of

patients, hence its alternative nomenclature of torus lateralis (lateral bulge ) .The anterior faceforms the posterior margin of the hiatus semilunaris and ethmoidal infundibulum. Posteriorly) the


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bulla may fuse with the basal lamella of the middle turbinate and superiorly it may reach the roof

of the ethmoids forming the posterior wall of the frontal recess. Sometimes a cleft is encountered

between the posterior wall of the bulla and the basal lamella of the middle turbinate, the retrobullarrecess. The space between it and the ethmoidal roof is called the suprabullar recess) which may

connect anteriorly with the frontal recess if the bulla does not reach the skull base. Suprabullar and

retrobullar recess may be continguous or may be separated by complete or incomplete bonyseptations. Contiguous) supra- and retrobullar recess may be defined as follows:

medial: middle turbinate;

lateral: lamina papyracea;

superior: roof of ethmoid;

inferior and anterior: unicate process;

posterior: basal Lamella of the middle turbinate.

ANATOM ICAL VARIATI ONSThere is a considerable range of anatomical variation in this area which has been implicated

in the aetiology of sinus infection (Figures 104.32, 104.33 and 104.34) Table 104. 1 ) . This

includes pneumatization of the middle turbinate) enlargement of the ethmoidal bulla) aparadoxically bent middle turbinate) everted uncinate processand the presence of infraorbital

(Haller cells) or a septaldeflection. The incidence with which these are seen in a'normal) population

may appear to be less frequent than in those individuals with chronic rhino sinusitis, but on closer

inspection it is clear that it is narrowing of the ostiomeatal complex rather than the existence ofthe variant which is the important factor.

ROOF OF ETH M O I D COM PLEX A N D ANTE R I O R ETH M O I DAL ARTERYIn a disarticulated dry skull, the ethmoid bone is open superiorly, at Least over its anterior

two-thirds (Figure 104.35). The bony cover for these open clefts and cells of the ethmoid is

provided by the frontal bone, which covers these open spaces with its foveolae ethmoidales (ossis

frontalis) . In this area, the frontal bone is both thicker and denser than the adjacent bony ethmoidalstructures. This difference is greatest medially, in the transition from the thicker bony lamellae of

the frontal bone to the much thinner lateral lamella of the cribriform plate. This lateral lamella

constitutes the lateral border of the olfactory fossa) with the lamina cribrosa providing its floor.The lateral 'lamella of the lamina cribrosa is also the medial wall of the dome of the ethmoid) the

height -and shape of which varies considerably from case to case. Keros and Kainz have assigned

a classification I-III to this surgically very important and critical area. It is here too) where thetopographic relationships of the anterior ethmoidal artery are especially important. The artery, in

its course from the orbit to the olfactory fossa and back into the nasal cavity) traverses thret

compartments of the head: the orbit, the ethmoidal Labyrinth) the anterior cranial fossa and finally

down into the nose again. The artery can be the source of significant intraoperative bleeding wheninjured. At the point where the artery enters the anterior cranial fossa through the lateral lamella

of the lamina cribrosa, the thinnest bony structures of the entire anterior skull base can be

encountered. It is here where the very thin lateral lamella of the lamina cribrosa presents the least

resistance to any instrument, with a bony thickness frequently only 10 percent as strong as the roofof the ethmoid.

After its origin from the ophthalmic artery in the orbit, the anterior ethmoidal artery passes

between superior oblique and medial rectus muscles, through the anterior ethmoidal foramen intothe anterior ethmoid complex. It crosses the anterior ethmoid either at the level of the ethmoidal


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roof or as much as 5 mm below this level, running in a mucous membrane fold or a thin bony

mesentery in the roof of the anterior etlunoidal sinuses. The artery may be surrounded by only a

thin-walled bony channel, which can be dehiscent in over 40 percent inferiorly. After thisoccasionally oblique passage through the anterior ethmoid, the artery enters the olfactory fossa,

i.e. intracranially through either the lateral lamella of the lamina cribrosa or where this attaches to

the frontal bone of the ethmoidal roof. The longer the lateral lamella of the cribriform plate, i.e.the deeper the olfactory fossaand with that, the higher the ethmoidal roof above the level of thecribriform plate - the more likely the ethmoidal artery is to be found travelling freely through the

ethmoid cavity and penetrating through the lateral lamella of the cribriform plate. After intracranial

entry, the artery turns anteriorly forming a groove in the lateral lamella, the so- called ethmoidalsulcus. Here, it gives off anterior meningeat branches and finally reaches the nasal cavity again

through the cribroethmoidal foramen and the cribriform plate. It is here where it divides into the

anterior nasal artery with superior, lateral and medial nasal branches, as well as a posterior branch.

This division may take place before or after its passage through the lamina cribrosa. The anteriorethmoidal artery has been estimated to be unilaterally absent in 14 percent, bilaterally absent in 2

percent and multiple in 30 percent. If the anterior ethmoidal artery is absent, it is replaced by a

branch of the posterior ethmoidal artery.The bony structures in the immediate vicinity of the anterior ethmoidal artery may show

remarkable variation in thickness. Those parts of the roof of the ethmoid that are formed by the

frontal bone are much thicker and stronger than the lateral wall of the olfactory fossa, which is

formed by the lateral lamella of the cribriform plate. The frontal bone at the roof of the ethmoidhas a mean thickness of 0.5 mm, whereas the lateral lamella of the cribriform plate averages only

0.2 mm. In the ethmoidal sulcus, the thickness of the wall may be reduced to 0.05 mm, and is

therefore by a factor of ten thinner than the roof of the ethmoid The length of the ethmoidal sulcuscan vary between 3 and 16 mm. The height of the lateral lamella of the cribriform plate is also

variable (1-17 mm) and the ethmoid roofs themselves are often asymmetric ( 1 0 percent) with the

right more often lower than the left.

At the calvarium, the dura mater is only loosely attached to skull In the region of theolfactory fossa, however, the dura is not only thinner, but is firmly attached to the bone, partially

where anterior ethmoidal artery and the olfactory filaments pass through the cribriform plate. In

the majority of cases, the anterior ethmoidal artery is intradural on its way through the olfactoryfossa. Trauma in this region, therefore, may easily lead to dural tears with subsequent CSF leakage

and, possibly, even intracranial bleeding from branches of the anterior ethmoidal artery.

SU PER I O R M EATUS

This meatus is again defined by its relationship to the superior turbinate. The posterior

ethmoidal cells open into this region.

A supreme turbinate is discernible above the superior meatus in 60--67 percent of subjects,though is well developed in less than 20 percent. Drainage to the corresponding supreme meatus

from the posterior ethmoidal system can take place under these circumstances.

POSTERI O R ETH MO I D CO M PLEXThe ground lamella of the middle turbinate is the border between anterior and posterior

ethmoidal sinuses. All clefts and cells opening posterior to the basal lamella belong to the posterior

ethmoid in the superior (and occasionally supreme) meatus. The sphenoid sinus ostium opens intothe sphenoethmoidal recess medial to the superior turbinate.


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The number of cells that make up the posterior ethmoid varies between one and more than

five. The topography of the most posterior cell of the posterior ethmoid, however, is of great

importance to sinus surgeons, since these cells can develop laterally and even superiorly to thesphenoid sinus. In these cases, the optic nerve and even internal carotid artery may bulge into these

sphenoethmoidal cells, named previously after the Austro-Hungarian, Onodi. The optic nerve

tubercle may appear very prominently on the lateral wall of such a cell and may, in fact, besurrounded by such cells.

SPH ENOETH M O I DAL RECESS

The sphenoethmoidal recess lies medial to the superior turbinate and is the location of theostium of the sphenoid sinus.

H I STOLOGY OF THE LATERAL WALL

The majority of the lateral wall is covered by respiratory ciliated columnar epitheliumthough there is a small variable area superiorly of olfactory epithelium spreading down from the

cribriform plate. Areas of squamous metaplasia are often found on the lateral wall, particularly in

areas subject to greatest airflow, such as the anterior inferior turbinate.

B LOOD SU PPLY OF THE LATERAL WALL

The external and internal carotid arteries supply the lateral wall (Figure 1 04.36) . The

sphenopalatine artery (from the maxillary artery and thus external carotid artery) contributes themajority of the supply to the turbinates and meatus. It enters through the sphenopalatine foramen

which lies just inferior to the horizontal attachment of the middle turbinate and may be damaged

in excessive enlargement of a middle meatal antrostomy. Its branches to the respective turbinatesand meatus enter posteriorly. On the conchae, the vessels are partially embedded in deep grooves.

In the inferior meatus, the sphenopalatine branch dips below the level of the palate to re-emerge

anteriorly, leaving the central portion of the meatus relatively avascular. An area anteriorly is

supplied by a branch from the facial and part of the lateral wall adjacent to the palate receivesblood from the greater palatine. The internal carotid artery contribution is via the ethmoidal arteries

which supply the superior lateral wall. There is considerable overlap between the internal and

external carotid arterial systems on each side and between the right and left sides which maycomplicate attempts at arterial ligation in the management of epistaxis.

The vascular supply to the nose is well-developed and this is enhanced by cavernous plexus

found in the lamina propria, in particular on the inferior and middle turbinates, which is controlledautonomically. The veins of the plexus are between 0. 1 and 0.5 mm wide and anastomose with

each other. In addition, numerous arteriovenous anastomoses are found in the deep mucosa and

around the glands. Venous drainage is to the sphenopalatine veins via facial and ophthalmic

vessels, intracranially via the ethmoidal veins to veins on the dura and to the superior sagittal sinusvia the foramen caecum.

N ERVE S U PPLY OF THE IJHERAL WALL

Apart from the olfactory supply on the superior concha, the lateral wall receives ordinarysensation from the anterior ethmoidal nerve anterosuperiorly and from branches of the

pterygopalatine ganglion and anterior palatine nerves posteriorly (Figure 104.37) . There is a small

area innervated by the infraorbital nerve anteriorly and an area of overlap between the ethmoidal


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and maxillary nerves. The anterior superior alveolar nerve sends a small branch to the anterior

inferior meatus which may be damaged in inferior meatal surgeryaffecting dental sensation.

LYM PHATIC DRAI NAG E OF TH E LATERAL WALL

The lateral wall drains with the external nose to the submandibular nodes anteriorly and to

the lateral pharyngeal, retropharyngeal and upper deep cervical nodes posteriorly.

B LOOD. N ERVES A N D LYM PHATIC DRAI NAG E O F ETH M O I D S I N U SES

The vascular supply is derived from the sphenopalatine and ethmoidal (anterior and

posterior) arteries and drains by corresponding veins. The ethmoid sinuses are innervated by theanterior and posterior ethmoidal nerves and orbital branches of pterygopalatine ganglion.

Lymphatics drain to the submandibular nodes anteriorly and retropharyngeal nodes posteriorly.

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