The greater petrosal nerve arises from the geniculate ganglion of the facial nerve in the petrous temporal bone and carries preganglionic parasympathetic fibres from the superior salivatory nucleus. It exits the petrous apex through the hiatus of the facial canal, traverses the middle cranial fossa on the anterior petrous surface, passes through the foramen lacerum, and unites with the deep petrosal nerve (sympathetic) to form the nerve of the pterygoid canal (Vidian nerve), which reaches the pterygopalatine ganglion to supply secretomotor fibres to the lacrimal gland and nasal glands.
| Origin | Geniculate ganglion of the facial nerve (CN VII) |
|---|---|
| Course | Leaves the petrous temporal bone through its hiatus into the middle cranial fossa, runs forward to the foramen lacerum, and joins the deep petrosal nerve to form the nerve of the pterygoid canal |
| Sensory |
|
The greater petrosal nerve (older name greater superficial petrosal nerve) is damaged in petrous temporal bone fractures at the geniculate ganglion, producing dry eye, reduced nasal secretion and loss of taste from the palate. Geniculate ganglion herpes zoster (Ramsay Hunt syndrome) can involve it together with the facial nerve. In middle fossa approaches to the internal auditory canal it is seen as a white strand on the floor of the middle cranial fossa and can be followed back to find the geniculate ganglion; traction on it during temporal lobe retraction is a common cause of postoperative dry eye. Aberrant regeneration after facial nerve injury can send salivary fibres along this pathway, causing crocodile tears.
A fracture through the geniculate ganglion damages the nerve, causing ipsilateral dry eye, reduced nasal secretion and loss of palatal taste, often with facial nerve palsy.
Aberrant regeneration after proximal facial nerve injury reroutes salivary secretomotor fibres to the lacrimal gland, so the eye waters during eating.
Pressure or traction on the nerve during temporal lobe retraction for internal auditory canal surgery can denervate the lacrimal gland and cause a postoperative dry eye.
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