Radiology of the Abdomen and Pelvis

And

Cross-Sectional Anatomy

MBS 208

Introduction to Basic and Clinical Anatomy

Overview Common imaging modalities for the

abdomen and pelvis How to read an abdominal plain film Visualizing anatomy through imaging

Spaces in the abdomen and pelvis The 4 abdominal quadrants Vascular anatomy in the abdomen and pelvis The colon, with attention to the right lower

quadrant The pelvis

Imaging Modalities for the Abdomen and Pelvis

Commonly Utilized Modalities

Ultrasound CT (computed

tomography) Radiography

Abdominal plain film Fluoroscopy

Hysterosalpingography

Other Modalities MRI

Magnetic resonance imaging

Nuclear medicine Gallium scan

Positron Emission Tomography (PET)

Jeffrey B. Mendel, M.D. 2007

X-ray Basics

The detector (film or digital) captures the xThe detector (film or digital) captures the x--rays that rays that penetrate the target and an image is createdpenetrate the target and an image is created

PA (anterior-posterior) view X-rays enter through back of chest and exit out front where they are detected

X-ray BasicsAttenuation of the x-ray

beam is affected by:

Tissue density

Tissue thickness

X-ray energy (kV)

Structural elements that attenuate the beam to a greater extent than air (black) or are less attenuating than bone (white) show radiographically in various shades of gray

Air

Soft Tissue

Fat

Bone

X - RAY --- FOUR BASIC DENSITIES

The spine, ribs, scapulae, and ribs attenuate the beam and are white

The heart and soft tissues are gray

The lungs and trachea are filled with air and are black

Why is there an air-fluid level in the stomach beneath the left hemidiaphragm?

What is black, white, and gray?

Answer: the patient was imaged in the upright position

Approach to plain film interpretation

1) What is the normal and variant anatomy? Is something absent? Is there an additional finding?

2) Check for clues in the skin and soft tissues 3) Then evaluate the bones

position/alignment, cortex, density, internal architecture, focal lesions

12

11

10

9

8

7

6

5

4

3

2

1

Cervical rib

Bilateral cervical ribs Polydactyly

Additional Findings:

That extra stuff

Whats wrong with this radiograph?

The heart and aortic arch are also on the right side (normally left-sided structures). This is known as situsinversus, a congenital variant.

Also note the absence of both clavicles.

Ultrasonography (ultrasound)

Uses sound waves of frequencies 2 to 17 MHz. (Audible sound is in the range of 20 Hz to 20 kHz.)

Like SONAR, images result from the propagation of sound waves through the body and their reflection from interfaces within the body

The time it takes for the sound waves to return to the transducer provides information on the position of the tissue in the body

Ultrasound

No ionizing radiation Uses sound waves to visualize structures

Very operator dependent Can not penetrate bone

Mainstay of diagnosis for: Ob-gyn (strong foothold' in Ob) Screening for vascular, abdominal & renal pathology Palpable lesions: Breast and MusculoskeletalMusculoskeletal Thyroid/neck pathology Pediatric / Young women

Gray scale = anatomy

Colour Doppler = velocity and direction

Gallstones

Fetus in utero

CT computed tomography Cross-sectional modality with capabilities for multiplanarreconstruction and dynamic imaging to assess vascularity

Tube rotates around the body and a circle of stationary detectors detects the penetrating x-rays forming an image

CT Computed Tomography

X-ray tube and a semicircle of detectors rotate around the body

Computer collects the data from the detectors and reconstructs a cross-sectional image (back-projection)

Tube and detectors spin continuously allowing for rapid imaging (helical CT) as with CT angiography

CT - Limitations

Ionizing radiation Requires contrast: IV and oral

Oral contrast requires prep time (1-2 hours) Iodinated contrast is nephrotoxic Iodinated contrast has fatality rate 1:50,000

even with low osmolar contrast

Patient must be supine (prone) $$$

MRI -Magnetic Resonance Imaging Uses a high-field magnet

to image the body Rapidly switching

magnetic field gradients align the precession of the H protons (water and fat)

When the gradients are turned off, a faint radiofrequency signal is produced

Image is reconstructed using Fourier transforms

Multiplanar and vascular assessment possible

External Magnetic Field Be

High B

Low B

Create a gradient in the magnetic field within the scanner so that it is high in one corner, lowest in the opposite corner.

Protons in the high-field region produces highest frequency signal

Be

Spin flips

Magnetic Resonance Imaging

Magnetic nuclei are abundant in the human body (H,C,Na,P,K) and spin randomly Since most of the body is H2O, the Hydrogen nucleus is especially prevalent

Patient is placed in a static magnetic field Magnetized protons (spinning H nuclei) in the patient align in this field like compass needles Radio frequency (RF) pulses then bombard the magnetized nuclei causing them to flip around

The nuclei absorb the RF energy and enter an excited state When the magnet is turned off, excited nuclei return to normal state & give off RF energy

The energy given off reflect the number of protons in a slice of tissue Different tissues absorb & give off different amounts of RF energy (different resonances) The RF energy given off is picked up by the receiver coil & transformed into images MRI offers the greatest contrast in tissue imaging technology (knee, ankle diagnosis) cost: about $1450 - $2000 time: 30 minutes - 2 hours, depending on the type of study being done

MRI: Cadillac of soft tissue imaging

Mainstay of diagnosis for Neurologic imaging Musculoskeletal imaging (after plain film) Magnetic Resonance Angiography

Angiography without iodinated contrast*

Expanding applications in chest, abdominal, Expanding applications in chest, abdominal, breast, and pelvic imagingbreast, and pelvic imaging

Visualizing Anatomy: Brain MRI

MRI of torn ACL MRI of moderately torn rotator cuff

MRI - Advantages True multiplanar imaging Intravenous contrast not usually required No ionizing radiation required Newer scanners and well-trained technologists

minimize problems with claustrophobia

MRI - Limitations Ferromagnetic objects

cause artifacts that limit imaging

Contraindicated for patients with Implantable devices:

cochlear implants, pacemakers*

Metal shavings in orbits Severe renal failure

Still requires more cooperation and longer time than CT

$$$$

Each image from CT, MR, PET, US or NM provides a 2D image

Stack enough thin sections together and you obtain a 3D volume matrix

If the width of the slices is similar to the size of the elements in the 2D matrix you can reconstruct images in any plane you choose or make 3D models of high resolution

How do you obtain 3D images from 2D slices?

Coronary Coronary CT Angiography may eventually replace invasive angiography -No arterial puncture = no risk of vascular damage3D view of the arteries and the adjacent organs

The Axial(horizontal) Section

An An axialaxial section is section is horizontal and horizontal and represents the plane represents the plane in which most CT is in which most CT is acquiredacquired

liverRight hemidiaphragm

LA

Ao root

LV

Ao

The Sagittal Section

A A sagittalsagittal section is in a plane section is in a plane running longitudinally frontrunning longitudinally front--toto--backback

The The midmid--sagittalsagittal section section divides the body into two divides the body into two symmetric halvessymmetric halves

spine

LA

PAAo

Bladder

The Coronal Section

Coronal sections are Coronal sections are in planes running in planes running sideside--toto--side side

A A coronalcoronal section is section is vertical perpendicular vertical perpendicular to the sagittal sectionto the sagittal section

RV LV

liverstomach

Ao PA

Fluoroscopy Dynamic radiography

Permits real-time evaluation of the gastrointestinal tract

Barium Swallow (esophagus) Upper GI Series (stomach) Small Bowel Follow-through Barium Enema (colon)

Barium (& air) is introduced by enema or swallowing

Barium appears white on the images (high density attenuates the x-ray beam)

Can assess both intrinsic (mucosal) and some extrinsic

(mass-effect) abnormalities

Nuclear Medicine - GI Bleeding Scan Evaluates bleeding, particularly from the lower GI tract

Radiopharmaceutical = Tc99m invitro labelled RBCs

Sequential 5 minute images acquired over an hour

Looking for progressive accumulation of tracer

Where is the bleeding on this scan ? Answer: Cecum

Injected Gallium-67 binds to transferrin & enters the extracellular space of tumor cells via permeable capillaries

9/03

Gallium Scan Used for lymphoma

staging & response

Baseline imaging determines whether the tumor is gallium-avid

Serial scans assess response to treatment and can distinguish scar from residual tumor

Baseline

11/03

Response to Rx

7/04

Lymphoma recurs

PET/CT Initial Scan 6 Month Follow up

Introduction The primary imaging modalities for the abdomen

and pelvis are plain film, ultrasound, and CT Most common indications for imaging include

pain, trauma, distention, nausea, vomiting, and/or change in bowel habits

Choice of modality depends upon clinical symptoms, patient age & gender, and findings on physical exam

Mastery of the anatomy within each quadrant can help explain particular symptoms, clinical presentations, and/or imaging findings

Reading the Abdominal Plain Film

Also known as the KUB (kidney, ureter, & bladder)

Use a systematic approach to interpretation Lung bases & diaphragms Bones Soft tissues

Abnormal calcifications Organs Bowel

Plain film in 3 year old patient with pain

Stomach

Reading the Abdominal Plain Film

Also known as the KUB (kidney, ureter, & bladder)

Use a systematic approach to interpretation Lung bases & diaphragms Bones Soft tissues

Abnormal calcifications Organs Bowel

Plain film in 3 year old patient with pain

Stomach

Colon

AP SUPINE ABDOMEN X-RAYGAS PATTERN

COLON

STOMACH

SM. BOWEL

Normal abdominal gas pattern with air in the stomach and scattered non-distended loops of large bowel and little small bowel gas present.

Small intestine-jejeunum & ileum

Transverse colon

Ascending colon

Descending colon

Small vs. Large Intestine

Horton KM et al, Radiographics. 2000

Colon has sacculations called haustra as teniae coli are shorter than the colonic wall

Colon is relatively peripheral but can be very mobile

Small bowel had plica circulares & is positioned centrally

>3 cm diameter and air/fluid levels on the upright suggests small bowel obstruction

Small bowel has plicae circulares,mucosal folds that extend across the entire diameter of the bowel

The colonic haustra indent the margin but do not extend acrossthe bowel

Liver

Gall bladder

stomachspleen

Plain Film Soft tissues : Liver, Spleen, & Kidney

St

Soft Tissue Structures: Subtle on KUB

Stom

ach

Stomach

Always check the lung bases for an infiltrate

Look for free air on the upright film: commonly beneath the right hemidiaphragm

Liver edge

diaphragm

Free air under right hemidiaphragm due to perforated duodenal ulcer

Whats Up on an Abdominal Film?

No gastric air bubble in left upper quadrant

Air/fluid level superimposed on heart

More Misplaced Air

HIATAL HERNIA

47

UPPER GI ORAL BARIUM CONTRAST

BARIUM ENEMA - RECTAL BARIUM CONTRAST

STOMACH

COLON

WITHOUT CONTRAST

NORMALESOPHAGUS

DIAPHRAGM

HIATAL HERNIA

DIAPHRAGM

*Note distended distal esophagus with herniation of gastric fundus into chest through esophageal hiatus.

This allows for reflux of gastric contents into esophagus.

Surgical clips in RUQ from prior cholecystectomy Appendicolith on plain film

rectum

Calcifications, Metallic Surgical and Foreign Bodies

Clinical-Anatomic Approach

Divide and conquer !!! Median and

transumbilical planes divide the abdomen and pelvis into 4 quadrants

Each quadrant has its own particular symptoms, clinical presentations, and/or imaging findings

The Right Upper Quadrant

What lives in the right upper quadrant?

Liver

Gallbladder

Hepatic Flexure of Colon Right kidney and adrenal gland

Clinically Important Hepatic Anatomy

Falciform ligament defines right from left lobe

Blood supply: 70% via portal vein 30% via hepatic artery

Left, middle, and right hepatic veins converge with IVC

Each of 8 liver segments have portal vein, hepatic artery, and bile duct (portal triad)

Normal Liver Normal Liver on contrast on contrast

CTCT

Lt lobe

Rt lobe

IVC

Sto

SpLK

APortal Vein

Gall bladder

P

Falciform Lig. Serves as ananatomical marker

between liver lobes

CrusCrus of diaphragmof diaphragm

Sto

CBD

PORTAL VEIN

Coronal and Axial imagesCT

US

Metastatic disease

Liver is the most common metastatic site after regional lymph nodes

Metastases from colon, stomach, pancreas, breast and lung primaries

Lower attenuation foci within the liver during portal venous phase

Hepatic duct

Common hepatic artery

Portal vein

Porta Hepatis Portal Triad

Splenic artery

Cystic artery

Clinically Important Biliary Anatomy Hepatic cells secrete bile into

caniculi Drain into interlobular bile

ducts Ducts merge into progressively

larger ducts, eventually R and L hepatic ducts

Merge in Porta Hepatis to form common hepatic duct

Joins with cystic duct to form common bile duct

Pass through pancreatic head to empty into duodenum via sphincter of Oddi

Common bile duct

Gallbladder

Gallstone is compressing the common bile duct blocking the flow of bile from the liver.

Blocked Biliary System

GALLSTONES15-30% calcify

Cirrhosis: End-stage Liver Disease

The left lobe & caudate lobe hypertrophy

Portal venous pressure rises causing Reversed portal venous flow (hepatofugal) Splenomegaly Varices Ascites

Bowel loops are positioned centrally due to the presence of ascites

Spleen

Varices

Liver

The Left Upper Quadrant

What lives in the left upper quadrant?

Spleen

Left lobe of liver

Splenic flexure Left kidney and adrenal gland

spleen

gall bladder

duodenum

stomach

liver

PylorusL2

L1

T12

Splenic rupture due to MVA

Blunt trauma The left package spleen, left kidney

The right package liver, right kidney

Midline left lobe liver, pancreas

HEPATIC / SPLENIC

LACERATION

Note rib fractures on x-ray

ENLARGED PALPABLE SPLEEN

Enlarged spleen raises issue of lymphoproliferative diseases or infection.

Midline Anatomy

What lives in the midline of the abdomen?

Pancreas

Stomach

Colon and small intestine Aorta and IVC

Pancreatitis = Inflammation of the pancreas

Normal pancreas on CT

Pancreas

liver

liver

Midline: Rectus abdominis muscle

with linea alba at midlineAnterolateral(Outer to Inner Layers):

External oblique muscle with aponeurosis joining anterior layer of the rectus sheath

Internal oblique muscle with rectus abdominismuscle

Transversis abdominismuscle

Transversalis fascia Peritoneum

Ventral HerniaAbdominal Wall

Hematoma in the Rectus Abdominis

Key arterial anatomy of the GI tract

Celiac artery (axis)- arises form the ventral surface of the aorta, just below the diaphragm, at the level of the lower half of T12

Superior mesenteric artery (SMA)- arises form the ventral surface of the aorta approximately 1 cm below the origin of the celiac at the level of the upper half of L1

Inferior mesenteric artery (IMA)- arises from the ventral surface of the aorta at the level of L3, approximately 3 cm above the aortic bifurcation

Abdominal Aortic Aneurysm (AAA)

Aorta dilates causing loss of laminar flow and intraluminalthrombus (non-enhancing region)

Aneurysms > 5cm in diameter are at high risk for rupture

Normal caliber aorta

Images of AAA courtesy of A. Davidoff MD

Infrarenal AAA with intraluminal thrombus

Right pelvic renal transplant as seen on MRA

MR Angiography

Celiac Artery (Axis)

In most Individuals (~65%) the celiac axis divides into three majorbranches

1. Left gastric2. Splenic3. Hepatic

Diagnostic Angiography, Kadir, 1986.

Ashley Davidoff, MD

SMAsmall bowel, right and transverse colonIMAleft colon, sigmoid colon and part of rectum

GI Vasculature:GI Vasculature:Demand andDemand and

SupplySupply

Clinically OrientedAnatomy, Mooreet al., 1999

SMA & IMA

IMALt colic

Marginal art of colon

Sigmoid and superior rectal art

Middle colic

splenic

renal

SMAIMA

GDA

cHA

CT Mesenteric Angiography

This has virtually replaced diagnostic angiographyThis has virtually replaced diagnostic angiography

No arterial puncture = no risk of vascular damageNo arterial puncture = no risk of vascular damage3D view of the arteries and the adjacent organs3D view of the arteries and the adjacent organs

Extravasation of contrast marking site of bleeding

Jejunal

Ileocolic

Right colic

SMA

Lower Intestinal Bleed

Bleeding scan first, if positive:

Arteriogram with possible embolization of bleeding vessel

Spaces in the Abdomen and Pelvis

Potential spaces in the abdomen and pelvis include: Intraperitoneal Spaces

Greater and lesser omentum

Retroperitoneal Extraperitoneal

Potential spaces are difficult to appreciate on dissection

Best seen on imaging, especially when filled with air or fluid

Peritoneal vs. Retroperitoneal Spaces

ANT

Intra-peritoneal organs are covered in a layer of peritoneum, a double layer of which (mesentery) connects them to the abdominal wall

Liver, stomach, spleen, gallbladder, small bowel & colon (cecum, transverse, sigmoid)

Retroperitoneal organs lie behind the posterior peritoneum

Kidneys, adrenal glands, aorta & IVC, duodenum, ascending and descending colon, pancreas,

Fluid in the peritoneal cavity

Scott Tsai, MD Fluid in lesser sac

Omentectomyclips

S

Panc

Liver

Greater and lessersacs communicate via the epiploicforamen

Greater sac Not all fluid is free flowing

Loculated ascites is common in later stage

ovarian carcinoma

Fluid in peritoneal cavity def: space

between visceral and parietal peritoneum

Fluid accumulates in dependent areas

MorrisonMorrisons pouchs pouch (the peritoneal reflection separating the liver from the retroperitoneal kidney) is the most dependent location while supine

The left and right paracolic paracolic guttersgutters are also dependent and commonly accumulate fluid

l. Paracolic gutterr. Paracolic gutter

Hepatorenalrecess (pouch of Morison)

The Lower Quadrants

Right: Cecum, ileocecal region, and appendix; ovary (if female)

Left: descending colon and ovary

Most common clinical entities in the lower quadrants are:

Right Appendicitis, inflammatory bowel disease (Crohns), colonic malignancy

Left Diverticulitis

Both Pelvic abnormalities

Appendicitis

Obstruction of appendiceal lumen leads to inflammation and/or rupture

Typically present with fever, nausea/vomiting, and periumbilical/right lower quadrant pain

Presence of calcified appendicolith (7-15%) and abdominal pain = 90% probability of acute appendicitis

Appendicitis

AppendicolithAppendicolith seen on bone windowseen on bone window

Normal

Inflamed

Inflamed appendix

Diverticulosis

Herniation of mucosa and submucosa through muscular layers

The Pelvis

What lives in the pelvis?

Female: Uterus and ovaries

Bladder

Male: Bladder

Prostate and seminal vesicles

CALYX

PELVIS

URETER

BLADDER

Urinary System

The right kidney appears swollen with stranding in the perinephric fat and a dilated collecting system (hydronephrosis)

A stone in the mid right ureter accounts for obstruction of the collecting system

Perirenal Peril

Hydronephrosis Nephrolithiasis

Non-obstructing stone

Perirenal space outlined

Extravasated Extravasated urine in the urine in the right right perirenal perirenal space due to space due to obstructive obstructive kidney stonekidney stone

Bladder stones or calculi with obstruction of the

collecting system

Bladder

Kidneys

Stones

Imaging of the Female Pelvis

Ultrasound is the most common modality used to image the uterus and ovaries

Hysterosalpingography is exclusively used to assess tubal patency (infertility evaluation)

Pelvic MR is used selectively to evaluate the uterus, ovaries and fetus

SacrumSacro-iliac

jointSacro- iliac

joint

Femoral headGreater

trochanter

Lesser trochanter

Superiorpubic ramus

Symphysis pubisInferior pubic ramus

Acetabulum

AP PELVIS

PELVIC VASCULAR TREE

4

5

6

1. ABDOMINAL AORTA

2. INTERNAL ILIAC ARTERY

3. EXTERNAL ILIAC ARTERY

4. LUMBAR ARTERY

5. COMMON FEMORAL ARTERY

6. COMMON ILIAC

Psoas major m.

Iliacus m.

diaphragm

Quadratuslumborum

Pelvic Viscera - Malebladder

prostate

rectum

Descending, sigmoid colon

Ascending colon

NOTE OBSTRUCTION

PROSTATE

Benign Prostatic Hyperplasia

This can obstruct the ureters entering the bladder leading to hydronephrosis and renal failure.

Pelvic Viscera - Female

uterus

bladder

uterus

rectum

Descending colon

Ascending colon

Rectouterinepouch

ovary

Uterine (Fallopian) tube

ovary

fundus

body

cervix

Normal Uterus on Sagittal MR

Image: St. Pauls HospitalVancouver, BC

extracted from their website:http://www1.stpaulshosp.bc.ca/

Myometrium:(homogeneous, moderate

to low signal)

Endometrium: homogeneous intense signal

B

V

A

R

P

UterusUterus Hysterosalpingography

Lower Uterine Segment

Uterine cavity

Ampullary segment

Isthmic Segment

Catheter

FimbriatedEnd

Normal

Infundibulary Segment

Contrast has been injected through a canula placed into the cervical os. Iodinated contrast flows retrograde with injection filling the uterine cavity with reflux into the fallopian tubes.

Imaging of the Fetus

US is the primary modality for imaging during pregnancy Gestational sac yolk sac fetal pole cardiac activity at

5.5-6 weeks gestation Full fetal survey typically performed at 16-18 weeks

MR used to evaluate specific developmental anomalies

9 week pregnancy

US

30 week pregnancy

MRI

Conclusions The primary imaging modalities for the abdomen

and pelvis are plain film, ultrasound, and CT Most common indications for imaging include

pain, trauma, distention, nausea, vomiting, and/or change in bowel habits

Choice of modality depends upon clinical symptoms, patient age & gender, and findings on physical exam

Mastery of the anatomy within each quadrant can help explain particular symptoms, clinical presentations, and/or imaging findings