A 31-year-old woman presents with an 8-month history of rectal bleeding, mucus passage, and tenesmus. She has chronic constipation with excessive straining and admits to digital disimpaction. Sigmoidoscopy reveals a solitary, shallow, well-circumscribed ulcer with fibrinous slough on the anterior rectal wall 7 cm above the dentate line, surrounded by hyperemic, polypoid, thickened mucosa. Biopsy demonstrates fibromuscular obliteration of the lamina propria with splayed muscularis mucosa and regenerative crypt distortion, without granulomas or crypt abscesses.
The condition marked **B** in the diagram is characterized by which of the following pathophysiologic mechanisms?
A. Paradoxical puborectalis contraction with dyssynergic defecation leading to internal rectal intussusception and mucosal ischemia
B. Transmural inflammation with skip lesions and granulomatous infiltration of the rectal wall
C. Acute vascular insufficiency from superior rectal artery occlusion in a patient with atherosclerotic disease
D. Chlamydial trachomatis L2/L3 infection causing acute hemorrhagic proctitis with stricture formation
Explanation
Why "Paradoxical puborectalis contraction with dyssynergic defecation leading to internal rectal intussusception and mucosal ischemia" is right
The condition marked B — Solitary Rectal Ulcer Syndrome (SRUS) — is fundamentally a functional defecation disorder caused by paradoxical contraction of the puborectalis during straining (dyssynergic defecation). This paradoxical contraction, combined with chronic excessive straining and internal rectal intussusception or prolapse, leads to repetitive mucosal trauma and ischemia. The pathognomonic histologic finding of fibromuscular obliteration (smooth muscle fibers extending upward from the thickened muscularis mucosa between crypts) is the direct consequence of this mechanical trauma and ischemic injury. The clinical presentation—chronic constipation, excessive straining, sensation of incomplete evacuation, and admission of digital disimpaction—are all hallmarks of obstructed defecation and dyssynergic defecation. Defecography would demonstrate internal intussusception, and anorectal manometry would show paradoxical anal pressure rise during attempted defecation (Sabiston 21e; AGA Functional Anorectal Disorders 2024).
Why each distractor is wrong
Transmural inflammation with skip lesions and granulomatous infiltration: This describes Crohn disease (marked A), not SRUS. Crohn disease presents with multiple skip lesions, granulomas on biopsy, perianal disease, and transmural involvement—none of which are present in this patient.
Acute vascular insufficiency from superior rectal artery occlusion: This describes ischemic proctitis (marked C), which presents with acute onset, vascular comorbidity (atherosclerosis, vasculitis), and acute hemorrhagic necrosis. SRUS is chronic and benign with a functional, not vascular, etiology.
Chlamydial trachomatis L2/L3 infection causing acute hemorrhagic proctitis: This describes sexually transmitted proctitis from lymphogranuloma venereum (marked D), which requires sexual exposure history, positive Chlamydia PCR, and acute painful proctitis—not the chronic functional disorder seen here.
High-YieldNEET PG
SRUS is a misnomer—lesions are solitary in only ~70%, and the key to diagnosis is the combination of dyssynergic defecation on functional studies, pathognomonic fibromuscular obliteration on biopsy, and anterior rectal wall location; biofeedback therapy is first-line definitive treatment.
Sabiston 21e; AGA Functional Anorectal Disorders 2024
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