During a canal wall down mastoidectomy, the surgeon removes bone in the triangle bounded anteriorly by the bony labyrinth, superiorly by the superior petrosal sinus and posteriorly by the sigmoid sinus. Entry deep to this triangle exposes which structure?

• A Middle cranial fossa dura
• B Internal acoustic meatus
• C Jugular bulb
• D Posterior cranial fossa dura ✓

Explanation

This is Trautmann's triangle, a dural-deficient area of retrolabyrinthine temporal bone. Bone removal between the labyrinth, the superior petrosal sinus and the sigmoid sinus exposes the dura of the posterior cranial fossa, giving access to the cerebellopontine angle. The middle fossa dura lies above the tegmen tympani, and the jugular bulb lies below, inferior to Trautmann's triangle.

Reference: Scott-Brown's Otorhinolaryngology and Head and Neck Surgery, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.