Which nerve is involved in Frey's syndrome?

Explanation

## Correct Answer: A. Auriculotemporal nerve Frey's syndrome (gustatory sweating) is a post-parotidectomy complication arising from aberrant regeneration of parasympathetic nerve fibres. The **auriculotemporal nerve**, a branch of the mandibular division of the trigeminal nerve (CN V3), carries parasympathetic fibres that normally innervate the parotid gland for salivation. During parotidectomy, the facial nerve (CN VII) is at risk of injury. The parasympathetic fibres originally destined for the parotid gland (via the glossopharyngeal nerve pathway) misdirect and reinnervate sweat glands in the skin overlying the parotid region. The auriculotemporal nerve, which supplies sensory innervation to the skin of the temporal and auricular region, becomes the conduit for these aberrant parasympathetic fibres. When the patient eats (gustatory stimulus), these misdirected parasympathetic fibres trigger sweating over the cheek and temple instead of salivation—hence "gustatory sweating." This occurs in 25–50% of parotidectomy patients in Indian surgical practice, though most cases are subclinical. The syndrome is named after Frey, who first described it, and the auriculotemporal nerve is the anatomical key to understanding the pathophysiology. ## Why the other options are wrong **B. Glossopharyngeal nerve** — The glossopharyngeal nerve (CN IX) carries parasympathetic fibres to the parotid gland via the otic ganglion and auriculotemporal nerve, but it is NOT the nerve involved in Frey's syndrome. The glossopharyngeal nerve is the preganglionic pathway, not the site of aberrant reinnervation. NBE may trap students who confuse the preganglionic parasympathetic pathway with the postganglionic nerve that actually reinnervates the sweat glands. **C. Oculomotor nerve** — The oculomotor nerve (CN III) innervates extraocular muscles and carries parasympathetic fibres to the ciliary muscle and pupil—it has no anatomical relationship to the parotid gland or facial region sweating. This is a clear distractor with no clinical relevance to parotid surgery or Frey's syndrome. Including CN III tests whether students can eliminate irrelevant cranial nerves. **D. Facial Nerve** — While the facial nerve (CN VII) is injured during parotidectomy and carries parasympathetic fibres to the lacrimal and submandibular glands, it is NOT the nerve involved in Frey's syndrome. The misdirected parasympathetic fibres travel via the auriculotemporal nerve (CN V3 branch), not the facial nerve itself. NBE exploits the fact that CN VII is damaged in parotidectomy, luring students into selecting it. ## High-Yield Facts - **Frey's syndrome** = gustatory sweating over parotid region post-parotidectomy due to aberrant parasympathetic reinnervation via auriculotemporal nerve. - **Auriculotemporal nerve** is a sensory branch of CN V3 (mandibular trigeminal) that becomes the conduit for misdirected parasympathetic fibres originally destined for salivation. - **Incidence** of Frey's syndrome is 25–50% post-parotidectomy in Indian surgical series, though most cases are subclinical and asymptomatic. - **Pathophysiology**: parasympathetic fibres from CN IX (glossopharyngeal) meant for parotid salivation aberrantly reinnervate sweat glands in temporal and cheek skin. - **Clinical trigger** is gustatory stimulus (eating, chewing, sour foods); sweating occurs ipsilateral to the parotidectomy side over temple and cheek. ## Mnemonics **FREY = Facial Regeneration Errors Yield (aberrant) sweating** Post-parotidectomy, facial nerve injury causes parasympathetic fibres to regenerate aberrantly. These fibres travel via the auriculotemporal nerve (CN V3 branch) and reinnervate sweat glands instead of salivary glands, causing gustatory sweating. **AuriTemporal = Aberrant parasympathetic pathway** Remember: **Auri**culotemporal nerve is the anatomical culprit in Frey's syndrome. It's a sensory nerve (CN V3) that gets hijacked by misdirected parasympathetic fibres post-parotidectomy. ## NBE Trap NBE pairs the facial nerve (CN VII) with parotidectomy complications to lure students into selecting it, since CN VII is indeed at risk during parotid surgery. However, the nerve actually involved in Frey's syndrome is the auriculotemporal nerve (CN V3 branch), which becomes the route for aberrant parasympathetic reinnervation. ## Clinical Pearl In Indian surgical practice, Frey's syndrome is often underdiagnosed because patients may not volunteer the symptom of sweating during eating. A simple bedside test—applying starch-iodine powder to the parotid region and asking the patient to eat a sour lemon—will turn the powder blue-black over the affected area, confirming the diagnosis. Most cases are cosmetically bothersome rather than functionally disabling and can be managed conservatively or with botulinum toxin injection. _Reference: Bailey & Love Ch. 38 (Parotid Gland Surgery); Robbins Ch. 16 (Nerve Regeneration and Aberrant Innervation)_