E3474. The Enemy Within: Intraluminal Causes of Mechanical Small Bowel Obstruction
  1. Umaseh Sivanesan; Queen's University
  2. Laura Wong; Queen's University
  3. Maera Haider; Queen's University
  4. Andrew Chung; Queen's University
Mechanical small bowel obstruction (SBO) is most frequently secondary to adhesions. The next most common etiologies are hernias and malignancies. These three etiologies cause over 80% of mechanical SBO. Intraluminal pathologies represent an uncommon cause of mechanical SBO.

Educational Goals / Teaching Points
Review intraluminal causes of mechanical SBO and their imaging findings.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We divide intraluminal causes of mechanical SBO into four broad categories: ingested, formed due to stasis, secondary to inflammation, and neoplastic. Ingestion: Ingested foreign bodies are a rare etiology of SBO. Only about 10% of foreign bodies progress past the stomach, and most resolve spontaneously, with less than 1% causing an SBO requiring surgical intervention. Smaller indigestible ingested foreign bodies accumulate until they form a bezoar, which can cause a SBO. Subtypes include: trichobezoars, made of hair; phytobezoars, made of indigestible fruit or vegetable fibres; and pharmacobezoars, made of undigested medications. Bezoars can be associated with psychiatric illness. Secondary to stasis: Some ingested materials are digested into stool, but are still retained within the small bowel, and can cause stercoral obstruction. These can be seen in bedbound elderly patients with chronic constipation. Less frequently, this occurs in younger patients with neurogenic or metabolic causes of constipation. For example, younger patients with cystic fibrosis can develop Distal Intestinal Obstruction Syndrome, wherein thickened mucosal secretions lead to thickened stool, causing SBO. Other stasis-related etiologies of SBO include primary enterolithiasis, i.e., dense calculi formed within the gastrointestinal tract. These frequently form in diverticuli, blind-ending pouches/structures, and surgical anastomoses. Inflammation: Gallstone ileus is a classic example of an inflammatory intraluminal cause of mechanical SBO, wherein a cholecysto-enteric fistula forms as a complication of chronic cholecystitis, and allows a gallstone to enter the small bowel and become impacted, resulting in obstruction. Strictures (e.g. Crohn’s disease or radiation-related) may also result in SBO. As opposed to scenarios whereby a severe stricture results in complete effacement of the small bowel lumen causing SBO, we focus on cases where upstream stasis or build up of particulate matter around ingested material too large to pass the stricture results in the formation of an obstructing intraluminal body. Neoplasm: The most common small bowel malignancy is adenocarcinoma, which can lead to obstruction due to mural involvement and constriction. More uncommonly, neoplasms may occupy the gastrointestinal lumen, resulting in obstruction. Examples include polyps and endophytic malignancies such as gastrointestinal stromal tumours.

Intraluminal pathologies are an uncommon but important cause of mechanical SBO.