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MI12 Medical Imaging
Abdominal Imaging
Toronto Notes 2019
Table 8. Abnormal Air on Abdominal X-Ray
Biliary vs. Portal Venous Air
“Go with the flow”: air follows the flow of bile or portal venous blood
Biliary air is most prominent centrally over the liver
Portal venous air is most prominent peripherally
Air
Extraluminal
Intraperitoneal (pneumoperitoneum)
Retroperitoneal
Intramural
(pneumatosis intestinalis)
Intraluminal Loculated Biliary
Portal Venous
Appearance
Upright film: air under diaphragm
Left lateral decubitus film: air between liver and abdominal wall
Supine film: gas outlines of structures not normally seen:
Inner and outer bowel wall (Rigler’s sign) Falciform ligament
Peritoneal cavity (“football” sign)
Gas outlining retroperitoneal structures allowing increased visualization:
Psoas shadows Renal shadows
Lucent air streaks in bowel wall, 2 types: 1. Linear
2. Rounded (cystoides type)
Dilated loops of bowel, air-fluid levels
Mottled, localized in abnormal position without normal bowel features
Air centrally over liver
Air peripherally over liver in branching pattern
Common Etiologies
Perforated viscus
Post-operative (up to 10 d to be resorbed)
Perforation of retroperitoneal segments of bowel: duodenal ulcer, post-colonoscopy
1. Linear: ischemia, necrotizing enterocolitis 2. Rounded/cystoides (generally benign): primary (idiopathic), secondary to COPD
Adynamic (paralytic) ileus, mechanical bowel obstruction
Abscess (evaluate with CT)
Sphincterotomy, gallstone ileus, erosive peptic ulcer, cholangitis, emphysematous cholecystitis
Bowel ischemia/infarction
Mechanical Obstruction
Usually dilated
Multiple air fluid levels giving “step ladder” appearance, dynamic (indicating peristalsis present), “string of pearls” (row of small gas accumulations in the dilated valvulae conniventes)
Dilated bowel up to the point of obstruction (i.e. transition point)
No air distal to obstructed segment
“Hairpin” (180°) turns in bowel
Table 9. Adynamic Ileus vs. Mechanical Obstruction
Feature
Calibre of Bowel Loops
Air-Fluid Levels
(erect and left lateral decubitus films only)
Distribution of Bowel Gas
Adynamic Ileus
Normal or dilated
Same level in the same single loop
Air throughout GI tract is generalized or localized
In a localized ileus (e.g. pancreatitis, appendicitis), dilated “sentinel loop” remains in the same location on serial films, usually adjacent to the area of inflammation
Colorectal Cancer: CT Colonography and Colonoscopy for Detection-Systematic Review and Meta-Analysis
Radiology 2011;259:393-405
Purpose: To assess the sensitivity of computed tomography (CT) colonography and optical colonoscopy (OC) for colorectal cancer (CRC) detection.
Methods: Systematic review and meta-analysis
of diagnostic studies evaluating CT colonography detection of CRC based on a priori eligibility criteria, in particular requiring both OC and histological confirmation of disease. Studies that also assessed true-positive and false-negative diagnoses with OC were used to calculate OC sensitivity. Sensitivity of CTC and OC for CRC was the main outcome. Results: 49 studies on 11,151 patients undergoing diagnostic study for detection of CRC were included.CTChasasensitivityof96.1%(95%CI 93.8%,97.7%)andOChasasensitivityof94.7% (95% CI 90.4%, 97.2%) for the detection of CRC. Conclusion: CTC is highly sensitive for the detection of CRC and may be a better modality for the initial investigation of suspected CRC, assuming reasonable specificity.
Abdominal Computed Tomography
• indicationsforplainCT:renalcolic,hemorrhage • indicationsforCTwithcontrast
■ IV contrast given immediately before or during CT to allow identification of arteries and veins ◆ portal venous phase: indicated for majority of cases
◆ biphasic (arterial and portal venous phases): liver, pancreas, bile duct tumours
◆ caution: contrast allergy (may premedicate with steroids and antihistamine)
◆ contraindication: impaired renal function (based on eGFR)
■ oral contrast: barium or water-soluble (water soluble if suspected perforation) given in most cases to
demarcate GI tract
■ rectal contrast: given for investigation of colonic lesions
Approach to Abdominal Computed Tomography
• lookthroughallimagesingestaltfashiontoidentifyanyobviousabnormalities
• look at each organ/structure individually, from top to bottom, evaluating size and shape of each area of
increased or decreased density • evaluate the following:
■ soft tissue window
◆ liver, gallbladder, spleen, and pancreas
◆ adrenals, kidneys, ureters, and bladder
◆ stomach, duodenum, small bowel mesentery, and colon/appendix
◆ retroperitoneum: aorta, vena cava, and mesenteric vessels; look for adenopathy in vicinity of
vessels
◆ peritonealcavityforfluidormasses
◆ abdominalwallandadjacentsofttissue
■ lung window
◆ visible lung (bases)
■ bone window
◆ vertebrae, spinal cord, and bony pelvis