Complete Full-Thickness Rectal Prolapse: Most Likely Cause
The most likely cause of complete full-thickness rectal prolapse is chronic straining during defecation (Option D), which leads to progressive weakening of pelvic floor support structures through repetitive mechanical stress and potential denervation injury. 1
Understanding the Pathophysiology
Chronic straining is the primary mechanism that drives rectal prolapse development, not simply "chronic constipation" as an isolated entity. 1 The key distinction is that the repetitive straining behavior—which can occur with various defecatory disorders including paradoxical pelvic floor contraction (dyssynergia)—causes progressive weakening of the pelvic floor support structures and fascia. 1
Why Chronic Straining (Option D) is Correct:
- Direct mechanical injury: Chronic increases in intra-abdominal pressure from straining directly weakens pelvic floor support structures over time 1
- Denervation injury: Repetitive straining causes direct or denervation injury to the pelvic floor musculature, which increases stress on the fascia and leads to progressive weakening 1
- Sphincter damage: When the pelvic floor is weakened by chronic straining, external prolapse is frequently complicated by fecal incontinence due to mechanical stretching and damage of the anal sphincters 1
Why Other Options Are Less Likely:
Old Age (Option B):
While rectal prolapse is more common in elderly patients (prevalence of 1% in adults over 65 years), 2 age itself is a risk factor rather than a direct cause. 1 The condition is "usually seen in extremes of life" 2 but the underlying mechanism remains chronic straining and pelvic floor weakness that accumulates over time.
Congenital Pelvic Floor Weakness (Option A):
This would be relevant primarily in pediatric populations where rectal prolapse occurs at the "extremes of life." 2 In adults, congenital weakness alone is insufficient to explain the development of complete prolapse without the additional factor of chronic straining.
Trauma to Levator Ani Nerve Supply (Option C):
While denervation injury is part of the pathophysiology, it typically occurs secondary to chronic straining rather than as an isolated traumatic event. 1 Direct trauma would be an uncommon cause compared to the cumulative effect of repetitive straining.
Clinical Context and Risk Factors:
Multiple risk factors typically coexist, including: 1
- Advanced age
- Menopause
- Vaginal multiparity
- Obesity
- Chronic straining (the key modifiable factor)
- Any conditions causing chronic increases in intra-abdominal pressure
Important Clinical Pitfall:
Do not attribute rectal prolapse solely to "constipation" without recognizing the broader context. 1 The actual mechanism is the repetitive straining behavior, which can occur with various defecatory disorders. Many patients with rectal prolapse actually have paradoxical pelvic floor contraction (dyssynergia) rather than simple constipation. 2
Epidemiology Supporting This Answer:
- Incidence: approximately 2.5 per 100,000 inhabitants 2
- Women:men ratio of 9:1 2
- The female predominance supports the role of multiparity and chronic straining as causative factors 1
Answer: D. Chronic constipation (more precisely, chronic straining associated with defecatory disorders)