Intraluminal causes of mechanical small bowel obstruction: CT findings and diagnostic approach

Intraluminal causes of small bowel obstruction (SBO) are less common than mural or extrinsic etiologies. This review categorizes intraluminal causes of SBO into four broad categories to provide a diagnostic framework for radiologic interpretation: 1) ingested contents, 2) bowel stasis, 3) inflammatory causes, and 4) neoplasms. Ingested materials can result in SBO when individual or accumulated contents are too large to pass, such as in the case of foreign bodies or bezoars. Bowel stasis causing SBO can be secondary to abnormal bowel function, such as in cystic fibrosis, reduced transit of contents at sites of narrowing such as surgical anastomoses, or the formation of enteroliths in diverticula which may subsequently dislodge and result in luminal obstruction. Inflammatory causes of SBO include strictures or fistulas that allow foreign bodies (such as gallstones) formed outside the bowel to enter the bowel lumen and cause obstruction. Finally, neoplasms can present as endophytic masses that occlude the bowel lumen through a ball-valve mechanism or serve as a lead point for intussusception. Recognizing the imaging features that are suggestive of intraluminal SBO is critical for accurate diagnosis and timely patient care.