Imaging of the Abdomen

WEBB BRANT et al

CT ABDOMEN

INTRAVENOUS CONTRAST AGENTS

• Opacifying blood vessels• Increasing the CT density of vascular abdominal organs• Improving image contrast

Delayed images• Contrast excretion by kidneys• Late enhancement• Prolonged retention of IV contrast agents

Low osmolar, non-ionic, iodine-based agents• Lower rate of adverse reactions

CT OF THE ABDOMEN

• Soft tissue windows• Liver windows• Lung windows• Bone windows

Spleen size • N up to 14cm

Adrenals: • N thickness up to 1cm• No convex margins

Kidneys• N up to 9-13 cm

Lymph nodes:• Retroperitoneum• Mesentery• Omentum• Porta hepatis• Pelvis

Blood vessels• Aorta• IVC• Celiac axis • SMA and IMA• Renal arteries and veins• Splenic vein• SMV• Portal vein

CT ARTIFACTS

Patient motion

Volume averaging• Display the average densities within the slice thickness instead of separate individual densities

Beam hardening• Increase in mean energy of the x-ray beam when it passes through an object

Noise: Quantum Mottle• NORMALLY

– Data are generated by x-ray photons striking CT detectors– More x-ray photons, the better the data– Fewer x-ray photons, more limited the data

• Caused by:– Reducing slice thickness to improve resolution and decrease volume averaging effect– Therefore reducing number of photons used to create the image

ANATOMY

• RIGHT SUBPHRENIC SPACE communicates around the liver with the ANTERIOR SUBHEPATIC and POSTERIOR SUBHEPATIC (MORISON’S POUCH)

• LEFT SUBPHRENIC SPACE communicates with LEFT

SUBHEPATIC SPACE

• Right and left subphrenic spaces are separated by FALCIFORM LIGAMENT and do not communicate

• LESSER SAC is the isolated peritoneal compartment between the stomach and pancreas

ANATOMY

• Lesser sac communicates with greater sac through FORAMEN OF WINSLOW

• Right subphrenic and subhepatic spaces communicates freely with pelvic peritoneal cavity by RIGHT PARACOLIC GUTTER

• The PHRENICOCOLIC LIGAMENT prevents communication of left subphrenic/subhepatic spaces and left paracolic gutter

• Pelvis communicates with both sides of the abdomen

ANATOMY

• Mesentery extends like fan from LIGAMENT OF TREITZ in LUQ

• Disease from above the ligament is directed to RLQ• Disease from below the ligament is directed to pelvis

• GREATER OMENTUM double layer of peritoneum from greater curvature of the stomach

• Ground for PERITONEAL METASTASES

PERITONEAL FLUID

Ascites• Exudative ascites• Neoplastic ascites• Chylous ascites

• Free IPF distends recesses of peritoneal cavity

PERITONEAL FLUID

• Serous ascites (-10 to +15 H)• Hemoperitoneum (45H)

• Exudative ascites by pancreatitis accumulates in lesser sac

• Peritonitis: peritoneum enhances after contrast

PERITONEAL FLUID

Pseudomyxoma peritonei• Complication of

mucocele of appendix or mucinous cystadenocarcinoma

• Loculations cause mass effect on liver and adjacent bowel

Mucinous cystadenocarcinoma:• Filling of peritoneal

cavity by gelatinous mucin

PERITONEAL CARCINOMATOSIS

• Diffuse metastatic seeding of the peritoneal cavity

Most common cancers:• Ovarian • Stomach • Pancreas• Colon

Preferential sites:• Pouch of Douglas• Right paracolic gutter• Greater omentum

PERITONEAL CARCINOMATOSIS

CT findings:• Ascites (loculated)

Tumor nodules • Soft tissue masses• Thickened parietal peritoneum

Omental cake• Thickened nodular tumor in greater omentum• Displaces bowel away from anterior abdominal wall

Serosal tumor implantations

Minute implants

PERITONEAL MESOTHELIOMA

• Rare• Rapidly fatal course

• Enhancing solid tumor of mesentery

ABSCESS

• For percutaneous drainage

Commonly located at:• Pelvic cavity • Subphrenic space• Subhepatic spaces

CT Features:• Loculated fluid collections• Internal debri, fluid fluid levels, septations and air-fluid• Well defined wall with irregular thickening• Thickened fascia• Fat planes obliterated

• Fine needle aspiration

CYSTIC ABDOMINAL MASSES

Differentials: • Abscess• Loculated ascites• Pancreatic pseudocyst• Ovarian cyst/ cystic tumor• Lymphocele• Cystic lymphangioma• Enteric duplication cyst• Cystic teratoma

CYSTIC ABDOMINAL MASSES

Lymphocele• Cystic mass containing lymphatic fluid• Compolication of surgery or trauma

CYSTIC ABDOMINAL MASSES

Cystic lymphangioma• Lymphocele that is congenital • Obstruction of lymphatic channels• Thin walled and multiloculated• Attenuation: water to fat density

MESENTERIC CYST:• Cystic lymphangioma of the mesenteryOMENTAL CYSTS• Cystic lymphangiomas of the greater omentum

CYSTIC ABDOMINAL MASSES

Enteric duplication cysts• Lined with GI MUCOSA• Attached to normal bowel

Cystic teratoma• Retroperitoneum, mesentery, omentum• Complex cystic and solid mass• Water and fat attenuation and calcification

VESSELS

Abdominal aorta• Left side of spine• Bifurcates at level of iliac crest• Does not exceed 3cm

• INFERIOR VENA CAVA• Right of aorta

Common Iliac Vessels• Bifurcates at PELVIC BRIM

VESSELS

EXTERNAL ILIAC VESSELS• Anteriorly to the inguinal triangle

INTERNAL ILIAC (HYPOGASTRIC) VESSELS• Posterior pelvis

VESSELS

CELIAC AXIS• Level of aortic hiatus in diaphragm

SUPERIOR MESENTERIC ARETERY• 1 cm below celiac axis

RENAL ARTERIES• From lateral aspect of aorta within 1 cm of SMA

INFERIOR MESENTERIC ARETERY• Anterior branch of aorta just above the bifurcation

ABDOMINAL AORTIC ANEURYSM

• Circumscribed dilatation of an artery

• All three layers of arterial wall (INTIMA, MEDIA, ADVENTITIA)

• Fusiform, saccular or spherical dilatation

• Outer to outer diameter >3cm• Risk of aneurysm increases from 5-7cm and above

• N: aorta tapers distally• AbN: aorta fails to taper distally

• Iliac arteries are aneurysmal if diameter >1.5cm

ABDOMINAL AORTIC ANEURYSM

• 90% begin below renal arteries (infrarenal abdominal aortic aneurysm)

• Inflammatory and fibrotic changes in perianeurysmal tissue may enhance ( this is NOT chronic leak of aneurysm)– May obstruct ureters

RUPTURE ABDOMINAL AORTIC ANEURYSM

• Lethal• Abdominal pain, hypotension, pulsatile abdominal mass

• Unenhanced CT enough to confirm dx

CT findings• Active arterial bleeding • Streaks and puddles of IV contrast within retroperitoneal hematoma

Iliac artery aneurysms• >3.5cm

• HYPERATTENUATING CRESCENT SIGN• Crescent shaped high attenuation within wall of intraluminal thrombus of abdominal aortic aneurysm• Sign of IMPENDING RUPTURE• Acute blood DISSECTING into outer weak wall

INFECTED AORTIC ANEURYSM

• Rare• Difficult to suspect• Highly prone to rupture• Also called MYCOTIC RUPTURE• Bacterial instead of fungal

AORTIC DISSECTION

• Tear in the lumina• Results in dilated segment with two lumina• Most common: thoracic aorta

• Intimal flap separating true and false lumen• Thrombosis in false lumen• False lumen is usually larger and contains thrombus

Beak sign• Junction of flap with outer wall of false lumen is an acute

angle

ABDOMINAL HERNIA

ABDOMINAL HERNIAComplications:• Incarceration• Strangulation• Instestinal obstruction• Pulmonary hypoplasia (infants)

DIAPHRAGMATIC HERNIATION

• Morgagni hernia• Bochdalek hernia• Hiatus hernia

Morgagni Hernia

• Through foramen of Morgagni• Adjacent to xiphoid process• Right side > left• Rarer than Bochdalek• Small• Anterior• Low risk of prolapse

Morgagni Hernia

• Main differential Diagnosis:• CARDIOPHRENIC FAT PAD

BOCHDALEK HERNIA

• Congenital• Posterior attachment of the diaphragm• Failure of PLEUROPERITONEAL MEMBRANE

closure• Retroperitoneal structures (kidney, spleen) may

herniate• Left side > right• Pulmonary hypoplasia• BBBBB (Bochdalek, Big, Back, Baby, Bad)

HIATUS HERNIA

• Herniation of stomach • Through esophageal hiatus of diaphragm

• Types:• Sliding hiatus hernia• Rolling (para-esophageal) hiatus hernia

SLIDING HIATUS HERNIA

• 95%• Gastro-esophageal junction (GEJ) displaced

more than 1cm above the hiatus• Normal upper limit of esophageal hiatus

15mm• Widened esophageal hiatus 3-4cm• Gastric fundus above the diaphragm: as a

retrocardiac mass (with air-fluid level)

ROLLING (PARA-ESOPHAGEAL) HIATUS HERNIA

• GEJ remains in normal position

HIATUS HERNIA

Differential Diagnosis• Retrocardiac lung abscess • Retrocardiac empyema• Epiphrenic esophageal diverticulum

Groin Herniation

• Direct inguinal hernia• Indirect inguinal hernia: more common than

direct• Femoral hernia• Obturator hernia

Direct Hernia

• Abdominal viscera • Weakness of posterior inguinal canal medial to

inferior epigastric vessels, through Hasselbach’s triangle

• Hasselbach’s triangle: – Base: inguinal ligament– Lateral: inferior epigastric vessel– Medial: lateral edge of rectus sheath

Direct Hernia

• Hernial sac directly protrudes through inguinal wall

• (Indirect: arise through deep ring and enter inguinal canal)

• Seldom extend to the scrotum• Due to weak transversalis fascia of Hasselbach

triangle• Risks: Chronic increase in abdominal pressure

Direct Hernia

• Less susceptible to strangulation (unlike indirect hernia) due to wide neck

• Lateral crescent sign (CT): crescent of fat

INDIRECT INGUINAL HERNIA• More common than direct• Males > females: persistence of processus

vaginalis during testicular descent• Enters inguinal canal through deep ring• Lateral to the inferior epigastric vessels• Passes inferomedially to emerge via

superficial ring into the scrotum

INDIRECT INGUINAL HERNIAComplications• Incarceration• Strangulation with bowel ischemia and

perforation• Intestinal obstruction

Femoral Hernia

• Protrusion of peritoneal sac through femoral ring into femoral canal

• Posterior and inferior to inguinal ligament• May contain preperitoneal fat, omentum, small

bowel etc.• Females

Femoral Hernia

• Inferior to inferior epigastric vessels• Medial to common femoral vein• Narrow funnel-shaped neck; compress femoral

vein engorged distal collateral ligaments

• Valsalva maneuver• Femoral vein should also dilate

PANTALOON HERNIA

• Dual hernia • Romberg’s hernia• Saddle bag hernia

• Ipsilateral concurrent direct and indirect inguinal hernias

• Hernial sac on both sides of inferior epigastric vessel

De Garengeot Hernia

• Femoral hernia containing the appendix

AMYAND HERNIA

• Appendix containing inguinal hernia

Obturator Hernia• Chronic increased intra-abdominal pressure

Howship Romberg Sign: • Compression of obturator nerve• Pain and paresthesia along inner aspect of

thigh

OBTURATOR HERNIA

Hernial neck passes through: • Obturator internus muscle• Obturator membrane• Obturator externus muscle

• May contain ovary and uterus

Lumbar Hernia

• Defect in lumbar muscles or posterior fascia• Below 12th rib and above iliac crest

• Two types:Grynfeltt-Lesshaft hernia (superior)• Through superior lumbar triangle• More commonInferior lumbar hernia (Petit Hernia)• Inferior lumbar triangle

Lumbar Hernia

Superior lumbar triangle• (Triangle of Grynfeltt Lesshaft Hernia)• Medial: quadratus lumborum• Superior: 12th rib• Lateral: internal oblique muscle• Floor: transversalis fascia and transversalis

muscle • Roof: external oblique and latissimus dorsi

Lumbar Hernia

Inferior lumbar hernia (Petit hernia)• Inferior: iliac crest• Anterior: external oblique muscle• Posterior: latissimus dorsi

Foramen of Winslow• Aka epiploic foramen• Passage between GREATER and LESSER

SAC• Greater sac: general peritoneal space• Lesser sac: omental bursa

Spigelian Hernia• Along semilunar line• Through transversus abdominis aponeurosis

(Spigelian fascia)

PARASTOMAL HERNIA

• Abdominal contents through abdominal wall defect in the stoma.

Epigastric Hernia

• Linea alba superior to umbilicus• Aka Fatty hernia of linea alba

Richter Hernia

• 10% of strangulated hernia• Progress more rapidly to gangrene• Obstruction less frequent

• Antimesenteric wall of bowel has herniated• Most common entrapped part: TERMINAL

ILEUM

Littre’s Hernia

• Hernia containing Meckel’s diverticulum• Aka persistent omphalomesenteric duct hernia

ABDOMINAL OPACITIES

ABDOMINAL OPACITIES

• Foreign bodies• Retained barium or fecal material in colonic

diverticulosis• Appendicolith• Dystrophic calcificiations• Calculi

Peritoneal Calcification

Psammoma bodies• Cystadenocarcinoma of the ovary• Fine sand like calcificationPseudomyxoma peritonei• Ring or arc like calcificaitons in pelvisTuberculous peritonitisMeconium peritonitisPeritoneal oil granulomaResult of continuous ambulatory peritoneal dialysis

Psammoma Bodies• Round calcific collections • Dystrophic calcification• Necrotic cells form focus for surrounding calcific deposition• Lammelated concentric calcified structure

• Papillary thyroid carcinoma• Papillary serous endometrial adenocarcinoma• Meningioma• Mesothelioma• Serious cystadenoCA of the overy• adenoCA of lung

Uterine Leiomyoma

• Uterine fibroids• Most common solid benign uterine neoplasm

Pseudomyxoma Peritonei

• Ascites due to rupture of mucinous tumour (mucinous tumor of appendix, appendiceal mucocele)

Two types:• Peritoneal adenomucinosis (adenoma)• Peritoneal mucinous carcinoma (mucinous

adenoCA)

Pseudomyxoma Peritonei

• Loculated collections of fluid with scalloping of abdomino-pelvic organs

• Centrally displaced bowel loops and scattered punctate or curvilinear calcifications

• Low attenuation loculated fluid in peritoneum, omentum and mesentery

• Echogenic peritoneal masses or ascites with echogenic particles

Pseudomyxoma Peritonei

• Fatal• Progressive disease• Recurrent bowel obstruction d/t fibrosis and

adhesions

Differential: • Peritoneal carcinomatosis• Peritoneal sarcomatosis• Peritonitis

Pancreatic CalcificationsPunctate intraductal calcifications• Acute alcoholic pancreatitis

– Preponderant cause of diffuse pancreatic intraductal calcification

• Chronic pancreatitis• Kwashiorkor

Smaller intruductal calcificationsLarger intraductal calcificationsDystrophic calcifications

Chronic Pancreatitis• Prolonged inflammatory and fibrosing process• Excessive alcohol consumption• Malnutrition

• TIGAR-O• Toxic metabolic• Idiopathic• Genetic• Autoimmune• Recurrent• Obstructive

Chronic Pancreatitis• Jaundice, malabsorption, diabetes

• Dilated main pancreatic duct• Pancreatic calcification• Change in size shape and contour• Pancreatic pseudocysts

• Low signal intensity on T1• Delayed contrast enhancement• Dilated side branches

• Parenchymal atrophy or enlargement• Dilated and beaded pancreatic duct with intraductal calcifications

Chronic Pancreatitis

• Hyperechogenic pancreas indicates fibrosis• Pseudocysts• Pseudoaneurysms• Ascites

Acute Pancreatitis

• Alcohol abuse: most common cause of chronic pancreatitis

• Gallstone passage/impaction: most common cause of acute pancreatitis

Acute PancreatitisCullen sign • Periumbilical bruising

Grey Turner sign• Flank bruising

• Pancreatic enzymes digest fascial layers, spreading inflammation

• Pancreatic fluid collections• Pseudocyst formation• Liquefactive necrosis of pancreatic parenchyma• Abscess• Vascular complicaitons• Fistula formation

Acute Pancreatitis

Necrosis absent:• Acute peripancreatic fluid collection (APFC)

first 4 weeks• Pseudocyst (encapsulated fluid) after 4 weeksNecrosis present:• Acute necrotic collections (ANC) first 4 weeks• Walled off necrosis (WON) after 4 weeks

Acute PancreatitisEmphysematous pancreatitis• Secondarily infected liquefactive necrosis

• Focal or diffuse parenchymal enlargement• Edema• Indistinct margins d/t inflammation• Surrounding retroperitoneal stranding• Liquefaction: lack of parenchymal enhancement• Infected necrosis: presence of gas• Abscess: cicumscribed fluid colleciton• Hemorrhage: high attenuation fluid

Pancreatic Pseudocyst• Most common cystic lesion of the pancreas

• Mass effect– Biliary obstruction– Gastric obstruction

• Secondary infection

• Disrupted pancreatic duct• Takes 4-6 weeks• Communication with pancreatic duct makes it problematic

(increase recurrence)

Pancreatic Pseudocyst• Hypoechoic or anechoic• Low attenuation surround by enhancing wall

• In contrast:• Intraparenchymal fluid collections are called acute necrotic collections (ANC) or

walled off necrosis (WON)

• Small (4-6cm) likely to resolve spontaneously

Indication for drainage: • Infection• Large size (>4-6cm)• Mass effect• Growth

Diaphragmatic Apertures

• Passage between thoracic and abdominal cavities

Three main:• Aortic hiatus• Esophageal hiatus• Vena cava foramen

• Lesser apertures:

Colonic Diverticulosis• Multiple diverticula• Left sided abdominal pain and constipation

Almost all are FALSE DIVERTICULA• Mucosa herniating through a DEFECT IN THE MUSCULARIS

and covered by overlying serosa

• Increased intraluminal pressure• Colon is shortened and hypertrophied (MYOCHOSIS COLI)

• Most common: SIGMOID and descending colon

Foramen of Winslow

• Aka Epiploic foramen• Passage between greater and lesser sac

• Greater sac: General peritoneal space• Lesser sac: Omental bursa

Foramen of WinslowBorders:• Anterior: HEPATODUODENAL LIGAMENT

– Free border of lesser omentum– Two layers– Contains: CBD, hepatic artery, hepatic portal vein

• Posterior: peritoneum covering the IVC• Superior: peritoneum covering caudate lobe of the liver• Inferior: peritoneum covering commencement of duodenum

and hepatic artery• Left lateral: GASTROSPLENIC and LIENORENAL

ligaments

Colorectal Carcinoma• Most common CA of GIT• Adenocarcinomas arising from pre existing adonomas (malignant

transformation; multi-hit hypothesis)

• Elderly• Younger for Rectal CA

Some risk factors:• Colonic adenoma (neoplastic polyps)• Inflammatory Bowel Disease• Dysplasia of colon within flat mucosa• Pelvic irradiation

Colorectal Carcinoma• Morphologically: sessile, exophytic, circumferential

(apple core), ulcerated, desmoplastic

• Right sided mass: larger mass, distant disease, iron deficiency anemia

• Left sided mass: present earlier with altered bowel habits

• From the cecum to the rectum• Recto-sigmoid 55%• Cecum and ascending colon 22%

Colorectal Carcinoma

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