This is a challenging case to rapidly put all of the findings together, particularly with the time pressures of an emergency department presentation.

First, the patient presented with findings typical of mesenteric ischemia (bright red blood per rectum and very high lactate), and thus underwent a multiphasic CT examination tailored for finding GI bleeding and mesenteric ischemia. Second, while it is pretty obvious that there is an abnormal small bowel loop in the right lower quadrant, the exact cause is not readily apparent. While the clustered, rounded appearance of this abnormal loop is characteristic for a closed-loop obstruction, your confidence in this diagnosis falters when you attempt to follow the small bowel distally out of this segment and find a longer-than-expected segment of normal caliber, decompressed ileum that you might give up on following until the second transition point. Only the proximal small bowel within the closed-loop becomes compromised (venous ischemia), and the remainder is not obstructed nor ischemic. Additionally, because there is such atherosclerotic disease, you might wonder if this patient has arterial (embolic) ischemia resulting in this finding. However, arterial ischemia would cause hyperenhancement without wall-thickening or as much mesenteric edema, and this case is more typical of venous ischemia. Finally, the diffuse dilation of the small bowel to the stomach is often misleading when reading cases of closed-loop obstructions, and requires you to observe differences of bowel wall thickness and enhancement involving the closed-loop to differentiate (both present in this case). 

Putting it all together, there is a long segment of mid and distal small bowel which has slid under an adhesive band in the right lower quadrant. The proximal small bowel is dilated with a short segment of fecalized small bowel leading into the proximal transition point at the adhesive band. The proximal closed loop segment has become ischemic as a result of impaired venous outflow, and these elevated venous pressures have also resulted intramural hemorrhage (accounting for higher density on non-contrast). The rest of the small bowel in this closed-loop segment has preserved blood flow (for the time being) and is not obstructed, and is therefore normal caliber leading into the distal transition point. Finding the distal transition point requires you to follow the bowel a bit longer than you might have expected to in a closed-loop case. 

However you might have read this case, it is practical to recognize quickly that this is a surgical abdomen, with small bowel ischemia in the right lower quadrant. Even if you failed to account for all of these particulars, appropriately sending the patient to the OR (versus to the floor with a nasogastric tube) will save his life.

Operative note excerpt: "There was a significant amount of blood in the abdominal cavity. We found a segment of inflamed mesentery and threatened small bowel in the distal jejunum that was herniating through an adhesive band between the sigmoid colon epiploica and pelvic sidewall. The  adhesion was lysed and the decision was made to resect a 40 cm of distal jejunum that looked threatened..."

Pathology report: Small bowel resection

• mucosal ischemic necrosis
• hemorrhage, vascular congestion, and edema