Facial Nerve Disorders: Topographic Diagnosis and Management
Core concepts
Understand the course of the facial nerve from the brainstem through the internal auditory canal, labyrinthine segment, geniculate ganglion, tympanic segment, and mastoid segment to the stylomastoid foramen. Topographic diagnosis uses associated symptoms: lacrimation (greater petrosal nerve, geniculate), stapedial reflex (stapedius, tympanic segment), and taste (chorda tympani, mastoid segment). Bell palsy is idiopathic lower motor neuron palsy; Ramsey Hunt syndrome adds vesicles (VZV). Upper motor neuron lesions spare the forehead. Know indications for steroids, antivirals, and surgical decompression, and when to suspect malignancy or cholesteatoma.
Traps in questions
- Forehead sparing indicates an upper motor neuron lesion, not Bell palsy.
- Hyperacusis localizes above the chorda tympani, near the stapedius.
- Loss of lacrimation localizes at or above the geniculate ganglion.
- Ramsay Hunt syndrome requires vesicles; antivirals are indicated with steroids.
- Do not diagnose Bell palsy without excluding other causes of facial palsy.
Worked rule of thumb
A patient with facial palsy, hyperacusis, and loss of taste has a lesion proximal to the chorda tympani but distal to the geniculate ganglion. If lacrimation is also lost, the lesion is at or above the geniculate ganglion.