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Toronto Notes 2019
Abdominal Imaging
Medical Imaging MI11
Table 7. Differentiating Small and Large Bowel
Property
Mucosal Folds
Location
Maximum Diameter Maximum Fold Thickness Other
Small Bowel
Uninterrupted valvulae conniventes (or plicae circularis)
Central
3 cm
3 mm
Rarely contains solid fecal material
Large Bowel
Interrupted haustra extend only partway across lumen
Peripheral (picture frame)
6 cm (9 cm at cecum)
5 mm
Commonly contains solid fecal material
3-6-9 Rule of Dilation
Small bowel (>3 cm) Large bowel (>6 cm) Cecum (>9 cm)
Approach to Abdominal X-Ray
• mnemonic:“FreeABDO” • “Free”:freeairandfluid
■ free fluid
◆ small amounts of fluid: increased distance between lateral fat stripes and adjacent colon may
indicate free peritoneal fluid in the paracolic gutters
◆ large amounts of fluid: diffuse increased opacification on supine film; bowel floats to centre of
anterior abdominal wall
◆ ascites and blood (hemoperitoneum) are the same density on the radiograph, and therefore,
cannot be differentiated
◆ free intraperitoneal air suggests rupture of a hollow viscus (anterior duodenum, transverse
colon), penetrating trauma, or recent (<7 d) surgery • “A”:airinthebowel(canbenormal,ileus,orobstruction)
■ volvulus – twisting of the bowel upon itself; from most to least common:
◆ sigmoid: “coffee bean” sign (massively dilated sigmoid projects to right or mid-upper abdomen)
with proximal dilation
◆ cecal: massively dilated bowel loop projecting to left or mid-upper abdomen with small bowel
dilation
◆ gastric: rare
◆ transverse colon: rare (usually young individuals)
◆ small bowel: “corkscrew sign” (rarely diagnosed on plain films, seen best on CT
■ toxic megacolon
◆ manifestation of fulminant colitis
◆ extreme dilatation of colon (>6.5 cm) with mucosal changes (e.g. foci of edema, ulceration,
pseudopolyps), loss of normal haustral pattern • “B”:bowelwallthickening
■ increased soft tissue density in bowel wall, thumb-like indentations in bowel wall (“thumb- printing”), or a picket-fence appearance of the valvulae conniventes (“stacked coin” appearance)
■ may be seen in IBD, infection, ischemia, hypoproteinemic states, and submucosal hemorrhage • “D”: densities
■ bones: look for gross abnormalities of lower ribs, vertebral column, and bony pelvis ■ abnormal calcifications: approach by location
◆ RUQ: renal stone, adrenal calcification, gallstone, porcelain gallbladder ◆ RLQ: ureteral stone, appendicolith, gallstone ileus
◆ LUQ: renal stone, adrenal calcification, tail of pancreas
◆ LLQ: ureteral stone
◆ central: aorta/aortic aneurysm, pancreas, lymph nodes
◆ pelvis: phleboliths (i.e. calcified veins), uterine fibroids, bladder stones • “O”: organs
■ kidney, liver, gallbladder, spleen, pancreas, urinary bladder, psoas shadow
■ outlines can occasionally be identified because they are surrounded by more lucent fat, but all are
best visualized with other imaging modalities (CT, MRI)
Figure 16. Normal AXRs: (left) supine anteroposterior AXR, (middle) upright anteroposterior AXR, and (right) left lateral decubitus AXR