The tympanomastoid fissure is one of the intrinsic fissures of the temporal bone, located parallel and posterior to the bony external auditory canal, dividing the tympanic part of the temporal bone and mastoid process. It gives passage to the auricular branch of the vagus nerve (Arnold's nerve) from the middle ear to the preauricular soft tissues. Its radiological significance is as a fracture mimic (pseudofracture) 1. Its surgical significance is as a commonly used palpable landmark to localise the facial nerve trunk during parotidectomy or repair after facial trauma 2.
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