Mechanism Linking Obstructive Müllerian Anomalies to Endometriosis
The proposed mechanism linking obstructive Müllerian anomalies to endometriosis is retrograde menstruation, whereby outflow obstruction causes increased retrograde flow of menstrual debris through the fallopian tubes into the peritoneal cavity, where endometrial fragments implant and proliferate. 1, 2, 3
The Retrograde Menstruation Theory
The pathophysiologic cascade operates through a specific mechanism:
- Outflow obstruction from Müllerian anomalies increases the volume and pressure of retrograde menstrual flow through the fallopian tubes into the pelvic cavity 3, 4
- Endometrial fragments reaching the pelvis via this increased transtubal retrograde flow implant onto the peritoneum and abdominal organs, where they proliferate and cause chronic inflammation with adhesion formation 2
- The number and amount of menstrual flows, combined with genetic and environmental factors, determines the degree of phenotypic disease expression 2
Clinical Evidence Supporting This Mechanism
The evidence strongly supports retrograde menstruation as the primary mechanism:
- Obstructive Müllerian anomalies show significantly higher rates of endometriosis compared to non-obstructive anomalies (p < 0.001), directly supporting the retrograde menstruation theory 3
- Non-obstructive Müllerian anomalies do not show increased endometriosis prevalence compared to controls (p > 0.05), further confirming that obstruction itself—not the anatomic anomaly—drives endometriosis development 3
- Studies demonstrate 19.8% endometriosis prevalence in patients with Müllerian anomalies overall, but this rate is driven entirely by the obstructive subgroup 3
Important Clinical Considerations
A critical pitfall: The association between obstructive anomalies and endometriosis is well-established, but the relationship is less clear in unobstructed anomalies and in rudimentary uterine structures lacking functioning endometrial tissue 1. This suggests retrograde menstruation requires both obstruction AND functioning endometrium to drive endometriosis development.
Congenital Obstructive Endometriosis
- A specific form of endometriosis can develop in adolescents with congenital uterine anomalies causing outflow obstruction, even before regular cyclic menstruation is fully established 5
- These lesions can include superficial peritoneal implants, adhesions, and endometriomas despite the young age at presentation 5
Clinical Implications
- Always specifically evaluate for endometriosis when diagnosing Müllerian anomalies, particularly obstructive types, as the prevalence reaches 74.9% in some surgical series 4
- The high coincidence rate means that failure to screen for endometriosis in patients with known obstructive anomalies represents a missed opportunity for early intervention 1, 4