Rectal Pain During Menses: Endometriosis Until Proven Otherwise
The most likely cause of rectal pain occurring exclusively during menstruation in a reproductive-age woman is bowel endometriosis, particularly involving the rectum or rectovaginal septum. 1, 2
Primary Diagnosis: Endometriosis with Bowel Involvement
Rectal pain during defecation that occurs only during menstruation is a highly specific clinical marker for rectal endometriosis, with this symptom independently predicting more extensive rectal disease (adjusted odds ratio 8.6,95% CI 1.8-41.2). 2 This cyclical pattern of dyschezia (painful defecation) with menstrual exacerbation should immediately raise suspicion for bowel or rectovaginal septum involvement. 1
Key Clinical Features to Identify
- Cyclical pattern: Pain strictly limited to menstrual periods is pathognomonic for endometriosis affecting the rectum 2, 3
- Associated symptoms: Look for dysmenorrhea, dyspareunia, constipation, and chronic pelvic pain 4, 1
- Defecation-related pain: Rectal pain specifically during bowel movements that coincides with menses is the hallmark finding 2
Diagnostic Approach
MRI pelvis is the preferred imaging modality for deep pelvic endometriosis, demonstrating 90.3% sensitivity, 91% specificity, and 90.8% accuracy. 5 MRI findings include:
- T2 hypointense fibrosis at the torus uterinus and uterosacral ligaments 5
- Obliteration of fat planes anterior to the rectum/sigmoid colon 5
- Obliteration of the pouch of Douglas 5
- T1 hyperintense hemorrhagic foci or T2 hyperintense glands may be present 5
Transvaginal ultrasound can also identify rectovaginal lesions and should be part of the initial evaluation. 4, 1
Critical Pitfall to Avoid
Do not assume gastrointestinal pathology and pursue extensive GI workup first. Upper endoscopy and colonoscopy typically show normal results in bowel endometriosis because the disease involves the serosal and muscular layers, not the mucosa. 3 The cyclical nature of symptoms should immediately direct evaluation toward gynecologic causes rather than primary GI disorders. 4
Alternative Diagnoses (Less Likely Given Strict Cyclical Pattern)
While other conditions can cause pelvic pain, the exclusive occurrence during menses makes endometriosis overwhelmingly most likely:
- Adenomyosis: Causes dysmenorrhea but typically presents with diffuse pelvic pain rather than isolated rectal symptoms 6, 7
- Pelvic inflammatory disease: Does not follow menstrual cyclicity 6, 7
- Irritable bowel syndrome: Pain pattern is not menstrually restricted 8
- Pelvic floor myofascial pain: Not cyclical with menses 6, 7
Management Framework
First-line empiric therapy for suspected endometriosis includes hormonal suppression of the menstrual cycle and/or analgesics. 1 However, the presence of dyschezia with cyclical exacerbation indicates a greater need for surgical management rather than prolonged medical therapy alone. 1
Surgical intervention may range from diathermy excision to full-thickness disc excision to segmental bowel resection, depending on disease extent. 2 A multidisciplinary approach with both gynecologic and colorectal surgical expertise is essential for optimal outcomes. 2
Important Caveat
Definitive diagnosis requires laparoscopic tissue biopsy, though careful pelvic examination and imaging may identify patients appropriate for empiric first-line therapy. 1 However, given the strong predictive value of cyclical rectal pain for extensive disease, these patients often require earlier surgical evaluation rather than prolonged empiric medical management. 1, 2