21 January 2009

Solution to the puzzle

The case I posed last week drew a lot of thoughtful comments, most of them more or less spot-on.   Answers and commentary below:

This upright abdominal x-ray shows multiple air-fluid levels, which are indicative of a bowel obstruction.   Most bowel obstructions are small-bowel obstructions, caused by intraperitoneal adhesions.  However, careful review of this shows dilation of the large intestine, indicated by the larger caliber of the air-filled segments and the transverse lines called haustra.  The air extends into the left lower quadrant and pelvis, indicating that the obstructive lesion is quite distal, in the recto-sigmoid region.  Therefore this is a distal large bowel obstruction.

The most common causes of this are, as correctly pointed out, sigmoid volvulus and colorectal cancer.

This abdominopelvic CT scan shows the obstructing lesion.  Rectal contrast was administered and bright, undiluted contrast can be seen filling the ascending rectal segment (to the right of the arrows).   The gut proximal to the lesion is markedly dilated with air-fluid levels, and there is some contrast present, indicating that the obstruction was not quite complete, though certainly high-grade.

This is consistent with an annular "napkin ring" or "apple core" adenocarcinoma of the colon, in which the cancer grows circumferentially around the lumen of the gut and the constricts inward.

In this case, the "high-dose narcotics" were indeed a red herring, which had caused other providers to dismiss his constipation and bloating as narcotic-related.  The patient did diclose on history that he had been having scybalous stools prior to the obstruction -- small, pebble-like lumps of poop, which can be related to the reduced diameter of the distal colon.

Congratulations to anonymous 1/19 2:26AM as the first correct response: you are hereby awarded my everlasting respect and admiration.


  1. That's a classical example of an "apple-core" stricturous colonic malagnancy which is more common in the left colon. The right colon usually has polypoidal intraluminal growths. You can see more examples of colorectal cancer on CT scan in this series on my blog


  2. So. No mallard, then?


  3. Thank you for sharing the x-ray pic and the explanation. I found my first case of "obstructive ileus" 3 days ago. There were air-fluid level (at upper quadrant only), dilatation of small intestines, and "herring bone appearance" at the intestine wall. The surgeon found there was an adhesion of ileum to the pelvis during the operation.


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