Home › Body Atlas › Nerves › Lesser Petrosal Nerve

Lesser Petrosal Nerve

nervus petrosus minor

The lesser petrosal nerve carries preganglionic parasympathetic fibres from the tympanic plexus (via the tympanic nerve from CN IX) to the otic ganglion, from which postganglionic fibres travel with the auriculotemporal nerve to the parotid gland. It crosses the anterior surface of the petrous bone in its own groove, passes through the foramen ovale (or the canaliculus innominatus), and reaches the otic ganglion in the infratemporal fossa.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The lesser petrosal nerve is the anatomical basis for Frey syndrome (gustatory sweating) after parotidectomy: aberrant regeneration of the divided lesser petrosal fibres into the sweat gland nerves of the overlying skin causes sweating in the parotid region during eating. The Frey test (iodine and starch applied to the skin with the patient eating lemon) maps the affected area. Botulinum toxin injection into the skin prevents sweating in Frey syndrome. The lesser petrosal nerve is sacrificed during middle fossa approaches to the petrous apex.

Pathology

Common Injuries & Conditions

Frey Syndrome from Lesser Petrosal Nerve Injury

Parotidectomy divides the lesser petrosal fibres, which regenerate aberrantly into the sweat gland innervation of the overlying facial skin; subsequent parotid-stimulating foods cause facial sweating and flushing in the parotid distribution (Frey syndrome), managed by botulinum toxin injection into the affected skin every 6-12 months.