A baby is born with an imperforate anus and a rectovesical fistula. This malformation results from failure of which embryological structure to divide properly?
- A Failure of the urorectal septum to fuse with the cloacal membrane ✓
- B Failure of the proctodeum to rupture
- C Arrest of Rathke's folds migrating posteriorly
- D Failure of the dorsal mesogastrium to rotate
Correct answer: A. Failure of the urorectal septum to fuse with the cloacal membrane
Explanation
The cloaca is divided into the urogenital sinus anteriorly and the anorectal canal posteriorly by the urorectal septum (formed by the fusion of Rathke's folds). If the urorectal septum fails to fuse completely with the cloacal membrane, both communication between the urinary and rectal canals (fistula) and ano-rectal abnormalities result. A rectovesical (or rectourethral) fistula indicates incomplete urorectal septum division. Failure of the proctodeum to rupture causes a simpler superficial imperforate anus without fistula.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.