First principle: three steps, three failure modes
The Müllerian ducts must form → fuse (caudally) → resorb the septum.
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The high‑yield discriminator: septate vs bicornuate
Both have a divided cavity; they differ externally:
| Septate | Bicornuate | |
|---|---|---|
| Defect | resorption | fusion |
| External fundal contour | normal/flat | indented (>1 cm cleft) |
| Management | hysteroscopic septum resection (often improves outcomes) | fundamentally different; metroplasty rarely |
MRKH — the formation extreme
46,XX, functioning ovaries (→ normal breasts/secondary sexual characteristics), absent/hypoplastic uterus and upper vagina, primary amenorrhoea, normal pubic hair. Ovaries are normal because they are not Müllerian (Concept 3). Screen for renal and skeletal anomalies.
Clinical consequences
- Unicornuate with a non‑communicating functional rudimentary horn → cyclical pain, haematometra, and a rupture‑risk if pregnancy implants there. 🚩
- Anomalies → infertility, recurrent loss, malpresentation.
Pitfalls
- Diagnosing septate vs bicornuate on HSG alone or cavity view alone.
- Forgetting the renal tract in any Müllerian anomaly.
Pearls
- 🎯 Form/fuse/resorb → agenesis‑unicornuate / didelphys / bicornuate / septate. Septate = normal outside; bicornuate = indented outside.
- 🩺 A cyclically painful adolescent with a unicornuate uterus — think obstructed rudimentary horn.
Next → From congenital structure to acquired support failure (Concept 25).