Applied microanatomy of the petrous internal carotid artery, greater superficial petrosal nerve, and tensor tympani muscle to improve safety during middle fossa surgery: laboratory cadaveric investigation

Background

Middle cranial fossa surgery is challenging due to the proximity of several neurovascular structures, such as the otic capsule, greater superficial petrosal nerve (GSPN), and petrous internal carotid artery (pICA). The concept of middle fossa triangles aids in the recognition of landmarks and increases the safety of middle fossa surgery. However, a definitive description of the microanatomical interrelationship between the pICA, tensor tympani, and GSPN in middle fossa surgery is lacking.

Methods

This study investigates the relationship between the GSPN, pICA, and tensor tympani to improve the safety of pICA exposure during surgery of the middle fossa. The middle fossae of 5 cadaveric heads (10 sides) were drilled to expose the GSPN, pICA, and tensor tympani. The crossing points between the pICA, GSPN, and tensor tympani were recorded for the proximal and distal pICA using a stereotactic navigation system. Distances between the crossing points and the borders of the horizontal pICA were calculated. The GSPN and pICA crossed in all specimens.

Results

The mean (SD) distance between the GSPN and pICA was 3.0 (4.9) mm proximally and 5.3 (2.8) mm distally. The tensor tympani was lateral to the pICA with a mean (SD) distance of 4.2 (1.9) mm in all specimens (proximally and distally), except in 1 specimen in which it crossed only the proximal pICA.

Conclusions

Drilling the Kawase triangle on the medial side of the GSPN is not universally safe because the pICA and GSPN frequently cross along the course of the horizontal pICA. The tensor tympani muscle may be used as a reliable landmark to systematically localize the pICA.