During middle ear exploration, a surgeon elevates a glomus tumour arising from the cochlear promontory. The tumour originates from tissue associated with which nerve lying on the promontory?

• A Greater petrosal nerve
• B Tympanic branch of the glossopharyngeal nerve (Jacobson's nerve) ✓
• C Chorda tympani nerve
• D Nerve of Arnold

Explanation

Jacobson's nerve, the tympanic branch of CN IX, enters via the tympanic canaliculus and forms the tympanic plexus on the cochlear promontory along with sympathetic fibres from the caroticotympanic nerves. Glomus tympanicum tumours arise from paraganglia associated with this plexus. The greater petrosal nerve runs over the geniculate ganglion area toward the foramen lacerum and has no promontory relation, killing that distractor.

Reference: Cummings Otolaryngology: Head and Neck Surgery, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.