The greater superficial petrosal nerve (GSPN) carries preganglionic parasympathetic fibres from the superior salivatory nucleus via the nervus intermedius, emerging from the geniculate ganglion of the facial nerve as the first branch of CN VII. It travels across the middle cranial fossa floor to enter the foramen lacerum, joins the deep petrosal nerve to form the vidian nerve (nerve of the pterygoid canal), and synapses in the pterygopalatine ganglion to supply the lacrimal gland, nasal, and palatal glands.
The GSPN is the pathway for lacrimal gland parasympathetic secretion and is responsible for crocodile tears (paradoxical lacrimation) when aberrant regeneration connects facial nerve fibres to the lacrimal pathway. It is also the site of the most common persistent complication of middle fossa acoustic neuroma surgery: the nerve is stretched during middle fossa retraction, producing post-operative dry eye. GSPN section is occasionally performed for cluster headache (as it carries parasympathetic fibres responsible for autonomic lacrimation in cluster attacks). The nerve is a landmark in middle fossa skull base approaches.
Middle fossa craniotomy for internal auditory canal tumours retracts the temporal lobe over the floor of the middle cranial fossa where the GSPN is visible as a white line running anteromedially from the geniculate ganglion; excessive pressure on the GSPN during temporal lobe retraction produces ipsilateral dry eye from lacrimal gland denervation.
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