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Imaging of the Abdomen
- 1. WEBB BRANT et al CT ABDOMEN
- 2. 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
- 3. 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
- 4. 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
- 5. 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
- 6. 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
- 7. 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
- 8. PERITONEAL FLUID Ascites • Exudative ascites • Neoplastic ascites • Chylous ascites • Free IPF distends recesses of peritoneal cavity
- 9. PERITONEAL FLUID • Serous ascites (-10 to +15 H) • Hemoperitoneum (45H) • Exudative ascites by pancreatitis accumulates in lesser sac • Peritonitis: peritoneum enhances after contrast
- 10. 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
- 11. 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
- 12. 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
- 13. PERITONEAL MESOTHELIOMA • Rare • Rapidly fatal course • Enhancing solid tumor of mesentery
- 14. 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
- 15. CYSTIC ABDOMINAL MASSES Differentials: • Abscess • Loculated ascites • Pancreatic pseudocyst • Ovarian cyst/ cystic tumor • Lymphocele • Cystic lymphangioma • Enteric duplication cyst • Cystic teratoma
- 16. CYSTIC ABDOMINAL MASSES Lymphocele • Cystic mass containing lymphatic fluid • Compolication of surgery or trauma
- 17. 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 mesentery OMENTAL CYSTS • Cystic lymphangiomas of the greater omentum
- 18. 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
- 19. 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
- 20. VESSELS EXTERNAL ILIAC VESSELS • Anteriorly to the inguinal triangle INTERNAL ILIAC (HYPOGASTRIC) VESSELS • Posterior pelvis
- 21. 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
- 22. 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
- 23. 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
- 24. 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
- 25. INFECTED AORTIC ANEURYSM • Rare • Difficult to suspect • Highly prone to rupture • Also called MYCOTIC RUPTURE • Bacterial instead of fungal
- 26. 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
- 27. ABDOMINAL HERNIA
- 28. ABDOMINAL HERNIA Complications: • Incarceration • Strangulation • Instestinal obstruction • Pulmonary hypoplasia (infants)
- 29. DIAPHRAGMATIC HERNIATION • Morgagni hernia • Bochdalek hernia • Hiatus hernia
- 30. Morgagni Hernia • Through foramen of Morgagni • Adjacent to xiphoid process • Right side > left • Rarer than Bochdalek • Small • Anterior • Low risk of prolapse
- 31. Morgagni Hernia • Main differential Diagnosis: • CARDIOPHRENIC FAT PAD
- 32. 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)
- 33. HIATUS HERNIA • Herniation of stomach • Through esophageal hiatus of diaphragm • Types: • Sliding hiatus hernia • Rolling (para-esophageal) hiatus hernia
- 34. 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)
- 35. ROLLING (PARA-ESOPHAGEAL) HIATUS HERNIA • GEJ remains in normal position
- 36. HIATUS HERNIA Differential Diagnosis • Retrocardiac lung abscess • Retrocardiac empyema • Epiphrenic esophageal diverticulum
- 37. Groin Herniation • Direct inguinal hernia • Indirect inguinal hernia: more common than direct • Femoral hernia • Obturator hernia
- 38. 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
- 39. 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
- 40. Direct Hernia • Less susceptible to strangulation (unlike indirect hernia) due to wide neck • Lateral crescent sign (CT): crescent of fat
- 41. 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
- 42. INDIRECT INGUINAL HERNIA Complications • Incarceration • Strangulation with bowel ischemia and perforation • Intestinal obstruction
- 43. 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
- 44. 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
- 45. 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
- 46. De Garengeot Hernia • Femoral hernia containing the appendix
- 47. AMYAND HERNIA • Appendix containing inguinal hernia
- 48. Obturator Hernia • Chronic increased intra-abdominal pressure Howship Romberg Sign: • Compression of obturator nerve • Pain and paresthesia along inner aspect of thigh
- 49. OBTURATOR HERNIA Hernial neck passes through: • Obturator internus muscle • Obturator membrane • Obturator externus muscle • May contain ovary and uterus
- 50. 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 common Inferior lumbar hernia (Petit Hernia) • Inferior lumbar triangle
- 51. 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
- 52. Lumbar Hernia Inferior lumbar hernia (Petit hernia) • Inferior: iliac crest • Anterior: external oblique muscle • Posterior: latissimus dorsi
- 53. Foramen of Winslow • Aka epiploic foramen • Passage between GREATER and LESSER SAC • Greater sac: general peritoneal space • Lesser sac: omental bursa
- 54. Spigelian Hernia • Along semilunar line • Through transversus abdominis aponeurosis (Spigelian fascia)
- 55. PARASTOMAL HERNIA • Abdominal contents through abdominal wall defect in the stoma.
- 56. Epigastric Hernia • Linea alba superior to umbilicus • Aka Fatty hernia of linea alba
- 57. 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
- 58. Littre’s Hernia • Hernia containing Meckel’s diverticulum • Aka persistent omphalomesenteric duct hernia
- 60. ABDOMINAL OPACITIES • Foreign bodies • Retained barium or fecal material in colonic diverticulosis • Appendicolith • Dystrophic calcificiations • Calculi
- 61. Peritoneal Calcification Psammoma bodies • Cystadenocarcinoma of the ovary • Fine sand like calcification Pseudomyxoma peritonei • Ring or arc like calcificaitons in pelvis Tuberculous peritonitis Meconium peritonitis Peritoneal oil granuloma Result of continuous ambulatory peritoneal dialysis
- 62. 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
- 63. Uterine Leiomyoma • Uterine fibroids • Most common solid benign uterine neoplasm
- 64. 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)
- 65. 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
- 66. Pseudomyxoma Peritonei • Fatal • Progressive disease • Recurrent bowel obstruction d/t fibrosis and adhesions Differential: • Peritoneal carcinomatosis • Peritoneal sarcomatosis • Peritonitis
- 67. Pancreatic Calcifications Punctate intraductal calcifications • Acute alcoholic pancreatitis – Preponderant cause of diffuse pancreatic intraductal calcification • Chronic pancreatitis • Kwashiorkor Smaller intruductal calcifications Larger intraductal calcifications Dystrophic calcifications
- 68. Chronic Pancreatitis • Prolonged inflammatory and fibrosing process • Excessive alcohol consumption • Malnutrition • TIGAR-O • Toxic metabolic • Idiopathic • Genetic • Autoimmune • Recurrent • Obstructive
- 69. 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
- 70. Chronic Pancreatitis • Hyperechogenic pancreas indicates fibrosis • Pseudocysts • Pseudoaneurysms • Ascites
- 71. Acute Pancreatitis • Alcohol abuse: most common cause of chronic pancreatitis • Gallstone passage/impaction: most common cause of acute pancreatitis
- 72. Acute Pancreatitis Cullen 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
- 73. Acute Pancreatitis Necrosis absent: • Acute peripancreatic fluid collection (APFC) first 4 weeks • Pseudocyst (encapsulated fluid) after 4 weeks Necrosis present: • Acute necrotic collections (ANC) first 4 weeks • Walled off necrosis (WON) after 4 weeks
- 74. Acute Pancreatitis Emphysematous 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
- 75. 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)
- 76. 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
- 77. Diaphragmatic Apertures • Passage between thoracic and abdominal cavities Three main: • Aortic hiatus • Esophageal hiatus • Vena cava foramen • Lesser apertures:
- 78. 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
- 79. Foramen of Winslow • Aka Epiploic foramen • Passage between greater and lesser sac • Greater sac: General peritoneal space • Lesser sac: Omental bursa
- 80. Foramen of Winslow Borders: • 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
- 81. 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
- 82. 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%
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