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Petrous Apex

apex partis petrosae

The petrous apex is the medial tip of the petrous temporal bone, pointing toward the clivus and forming the posterior boundary of the foramen lacerum. It is closely related to the sixth cranial nerve in Dorello canal superiorly, the internal carotid artery in the carotid canal laterally, and the petroclival synchondrosis medially. The apex may contain air cells continuous with the mastoid, cholesterol granuloma fluid, or be solid bone.

Region: Head & Skull

Clinical Relevance

Clinical Notes

Petrous apex lesions include cholesterol granuloma (most common, benign cyst with brown-yellow fluid), cholesteatoma, and petrous apex meningioma. They present with CN VI palsy producing abducens palsy (Gradenigo syndrome: otitis, diplopia, retro-orbital pain) from compression in Dorello canal. MRI distinguishes cholesterol granuloma (T1 bright, T2 bright) from cholesteatoma (T1 dark, T2 bright). Drainage is via endoscopic or open petrosal approaches.

Pathology

Common Injuries & Conditions

Cholesterol Granuloma of the Petrous Apex

Expansion of a petrous apex cholesterol granuloma compresses the sixth cranial nerve in Dorello canal producing abducens palsy and diplopia (Gradenigo syndrome), managed by transsphenoidal or infralabyrinthine endoscopic drainage and stenting of the cyst to the sphenoid sinus.