Mechanical causes

1. Colorectal carcinoma - most common cause
2. Diverticular stricture / diverticulitis - particularly sigmoid colon
3. Volvulus - twisting of bowel, usually:
   • Sigmoid volvulus
   • Cecal volvulus
4. Extrinsic compression - pelvic, ovarian, metastatic, or other intra-abdominal malignancy
5. Benign strictures - due to Crohn disease, ischemic colitis, radiation, or prior inflammation
6. Fecal impaction
7. Hernia - incarcerated external or internal hernia
8. Intussusception - uncommon in adults, often associated with a lead-point lesion
9. Adhesions - much less common than in small-bowel obstruction

Functional causes

1. Acute colonic pseudo-obstruction (Ogilvie syndrome)
2. Paralytic/adynamic ileus, including that caused by opioids, severe illness, electrolyte disturbance, or postoperative state
3. Toxic megacolon - for example, with severe C. difficile colitis or inflammatory bowel disease