Infralabyrinthine approach to the petrous apex

This study measures the anatomical dimensions of the path to the petrous apex (PA) via the infralabyrinthine approach in temporal bones of adult Indian subjects, and studies the anatomical variation encountered in this approach. Forty-two temporal bones were dissected to gain access to the PA via the infralabyrinthine approach. The horizontal and vertical dimensions of the access window created as well as the length of the track to the PA from the vertical portion of facial nerve were measured with two-point calipers. Complete dissection was possible in only 21 bones (50%). In the remainder, after preliminary cortical mastoidectomy, an access window to the PA could not be created due to a high jugular bulb. The mean dimensions of the window in dissected bones were 4.60 mm vertically (SD = 0.94 mm) and 6.45 mm (SD = 1.44 mm) horizontally, and the depth of the track to the PA was 30.26 mm (SD = 3.62 mm). The infralabyrinthine approach to the PA provides wide access to lesions of the posterior and inferior PA. In up to 50% of temporal bones, as evidenced by this series, access may be limited by a high jugular bulb. The possibility of this anatomical variation should be considered when the surgical approach to a PA lesion via the infralabyrinthine approach is being planned.