Overview
This lecture explains Mullerian anomalies, their embryologic origins, genetic and hormonal factors involved in reproductive tract development, types of anomalies, clinical implications, and diagnostic approaches.
Embryologic Origins of the Reproductive Tract
- The reproductive tract develops from the intermediate mesoderm beginning in the third week of embryogenesis.
- The urogenital ridge forms the ovary/testes (genital ridge), kidneys (nephrogenic cord), and Mullerian ducts (paramesonephric ducts).
- Paramesonephric (Mullerian) ducts form the fallopian tubes, uterus, and upper two-thirds of the vagina.
- Mesonephric (Wolffian) ducts develop into male genital ducts in the presence of specific genes and hormones.
Genes and Hormones in Sexual Differentiation
- The SRY gene on the Y chromosome encodes the SRY protein (testes-determining factor).
- SRY protein leads to testes development and production of anti-Mullerian hormone (AMH) and testosterone.
- AMH causes regression of Mullerian ducts in males; testosterone supports Wolffian duct development.
- In females (absence of SRY/AMH/testosterone), Mullerian ducts persist, forming female reproductive structures.
Types and Causes of Mullerian Anomalies
- Mullerian anomalies result from abnormal development, fusion, or resorption of the Mullerian ducts.
- Bicornuate uterus: partial fusion of Mullerian ducts, leading to two uterine horns.
- Unicornuate uterus: asymmetric lateral fusion defect, one developed cavity.
- Uterine didelphys: complete failure of duct fusion, leading to double uterus.
- Septate uterus: incomplete resorption of the septum between fused ducts.
- Arcuate uterus: mild fundal indentation with a normal outer contour.
- Mullerian agenesis (MRKH syndrome): absence or underdevelopment of Mullerian structures, often with absent vagina.
Associated Vaginal and Renal Anomalies
- Transverse vaginal septa arise from failed Mullerian duct fusion or canalization; may occur at any vaginal level.
- Longitudinal vaginal septum results from defective lateral fusion, often associated with uterine didelphys.
- Ovarian development is separate; normal breast development occurs in females with Mullerian anomalies.
- Renal anomalies occur in 20-30% of women with Mullerian defects; evaluation is required.
Clinical Implications and Diagnosis
- Many women are asymptomatic; symptoms may include pelvic pain, menstrual abnormalities, and infertility.
- Obstetric complications: recurrent pregnancy loss, fetal growth restriction, malpresentation, preterm labor, retained placenta, and rarely uterine rupture.
- Diagnosis: MRI is the gold standard; ultrasound, hysterosalpingogram, and hysteroscopy are less invasive but may miss certain anomalies.
Key Terms & Definitions
- Mullerian anomalies — Congenital abnormalities of the uterus from improper formation/fusion of Mullerian ducts.
- SRY gene — Sex-determining gene on Y chromosome critical for male sexual differentiation.
- Anti-Mullerian hormone (AMH) — Hormone causing regression of Mullerian ducts in males.
- Bicornuate uterus — Uterus with two horns due to partial duct fusion.
- Uterine didelphys — Double uterus from failed duct fusion.
- MRKH syndrome — Congenital absence or underdevelopment of the uterus and/or vagina.
- Septate uterus — Uterus with residual septum from incomplete resorption.
Action Items / Next Steps
- Review embryology of the urogenital tract.
- Understand genetic/hormonal pathways in sexual differentiation.
- Memorize types and features of Mullerian anomalies.
- Prepare for imaging-based diagnosis questions.