Slide 1: Which one of these patients has a small bowel obstruction?
Slide 2: Evaluation of bowel gas patterns: the two most important components are diameter and distribution.
Diameter/Dilation: Follows the 3-6-9 rule. Small bowel less than 3 cm. Colon less than 6 cm. Cecum less than 9 cm.
Distribution: One. Start at rectum. Rectal gas equal bowel motility. Two. Identify pattern of gas. Small bowel (central). Colon (peripheral). Diffuse (both equal).
Normal bowel gas pattern: One. No abnormal dilation. Two. Gas distribution mostly in colon rather than small bowel. Three. Rectal gas present.
Slide 3: This is worrisome for a small bowel obstruction. Dilated small bowel bowel with decompressed colon and rectum.
What is wrong with this patient? One. Dilation: Present. The small bowel is 4.6 cm (normal 3 cm). Two. Distribution: Abnormal. The pattern is small bowel predominant. There is very little gas in the colon – it is decompressed. Three. Rectal gas: Absent. There is small bowel projecting over the pelvis but no clear rectal gas.
The valvulae coninventes confirm this is small bowel.
Slide 4: This is consistent with ileus. The bowel is immobile and filling with gas but since it is diffuse, there’s likely no physical obstruction.
What is wrong with this patient? One. Dilation: Present. The colon (haustral folds visible) is dilated greater than 6 cm. The small bowel is likely also dilated. Two. Distribution: Diffuse. The colon and small bowel are dilated about evenly. Three. Rectal gas: Absent. This suggests the bowel is not moving much.
Slide 5: Let’s review! Remember to look for abnormal dilation, determine if rectal air is present and identify the pattern of gas distribution.
Gas pattern. Normal. Dilation. No. Distribution. Colon predominant. Rectal air. Yes.
Gas pattern. SBO. Dilation. Yes. Distribution. Small bowel predominant. Rectal air. No.
Gas pattern. Adynamic ileus. Dilation. Yes. Distribution. Even distribution in colon and small bowel. Rectal air.
Tags: bowel gas, gastrointestinal, radiology, reading room