Pathophysiology of Stercoral Rectal Ulcer
Stercoral rectal ulcers develop when impacted, dehydrated fecal matter compresses the colonic mucosa and underlying vasculature, causing pressure-induced ischemic necrosis that progresses to full-thickness ulceration.
Mechanism of Injury
The pathophysiologic cascade begins with chronic fecal impaction, typically in the rectosigmoid region. The dense, inspissated stool (fecaloma) creates sustained mechanical pressure against the bowel wall. This pressure directly compresses the vascular supply of the distal colon, leading to mucosal ischemia and subsequent ulceration 1. The process represents pressure necrosis of the colonic mucosa rather than a primary inflammatory condition 2, 3.
Anatomic Distribution
The rectum is overwhelmingly the most common site, involved in approximately 98% of mild cases and 69% of moderate-to-severe cases 4. However, when perforation occurs, the sigmoid colon becomes the predominant location (95% of perforated cases), with 65% of perforations occurring without rectal involvement 4. This distribution pattern reflects both the anatomic narrowing at the rectosigmoid junction and the relative fixation of these segments.
Vascular Compromise
The ischemic process is central to ulcer formation. Luminal distention from the fecaloma compresses the intramural blood vessels, reducing perfusion to the mucosa and submucosa 1. This vascular insufficiency, combined with direct mechanical trauma, creates localized areas of mucosal integrity loss 2. The ischemia progresses from superficial mucosal injury to full-thickness necrosis if the impaction persists.
Progression to Complications
Once the ulcer forms, it can extend through all layers of the bowel wall. The most catastrophic complication is perforation, which occurs when the pressure necrosis creates a full-thickness defect 2. Perforation may be intraperitoneal or extraperitoneal depending on anatomic location. Other complications include massive hemorrhage from erosion into submucosal vessels, obstruction from the mass effect of impacted stool, and rarely fistula formation 1.
Risk Factor Context
The condition predominantly affects patients with impaired colonic motility. Advanced age, neurodegenerative disorders, chronic medical diseases, immobility, and medications that slow bowel transit (particularly opioids and anticholinergics) all contribute to the development of severe constipation and fecal impaction 1, 5. Notably, opioid use specifically increases perforation risk (50% vs 23% in non-perforated cases, p=0.04) 4.
Clinical Caveat
The pathophysiology differs fundamentally from inflammatory colitis—this is a mechanical and ischemic process, not a primary inflammatory disease, though secondary inflammation develops around the ulcerated tissue 1. This distinction is critical because the treatment approach focuses on relieving the mechanical obstruction rather than immunosuppression or anti-inflammatory therapy.