A patient with a basal skull fracture through the petrous temporal bone develops loss of taste from the anterior two-thirds of the tongue and hyperacusis (hypersensitivity to loud sounds), but facial motor function is intact. Where is the lesion along the facial nerve pathway?

• A Between the geniculate ganglion and the nerve to stapedius, above the chorda tympani takeoff
• B Distal to the stylomastoid foramen, at the parotid plexus
• C Between the nerve to stapedius and the chorda tympani, in the mastoid segment ✓
• D At the internal acoustic meatus, proximal to the geniculate ganglion

Explanation

The chorda tympani (carrying taste from anterior two-thirds tongue) and the nerve to stapedius are both branches of the mastoid segment of the facial nerve. Hyperacusis results from loss of stapedius muscle function. A lesion between the departure of the nerve to stapedius (above) and the chorda tympani (below) in the descending mastoid segment of CN VII produces hyperacusis and loss of taste without facial motor weakness because the main motor trunk is intact. A lesion proximal to the stapedius nerve would additionally cause hyperacusis; lesions distal to chorda tympani takeoff would spare taste.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.