A 15-year-old boy comes to the office due to right ear itching and discomfort for the past several days. He has no fever or hearing loss but has noted scant drainage of thin, whitish fluid. The patient has been taking swimming lessons at a local gym. On examination, there is no redness around the ear, but gentle traction of the pinna elicits pain. During inspection of the external auditory canal, a speculum is inserted into the meatus in close contact with its posterior wall, causing the patient to suddenly become lightheaded and faint. He recovers spontaneously within a few minutes with no residual confusion. Which of the following nerves was most likely irritated during the procedure?
Show Explanatory Sources
The majority of the external ear receives cutaneous innervation from the great auricular nerve, lesser occipital nerve, and auriculotemporal nerve. Most of the external auditory canal, including the external portion of the tympanic membrane, is innervated by the mandibular division of the trigeminal nerve (cranial nerve [CN] V3) via its auriculotemporal branch.
However, the posterior part of the external auditory canal, as well as the concavity and posterior eminentia of the concha, is innervated by the small auricular branch of the vagus nerve (CN X). This patient has experienced vasovagal syncope after stimulation of his posterior external auditory canal by an otoscope speculum. In this form of syncope, parasympathetic outflow via the vagus nerve leads to decreased heart rate and blood pressure.
(Choice A) The accessory nerve (CN XI) provides voluntary motor innervation to the trapezius and the sternocleidomastoid.
(Choice B) The facial nerve (CN VII) has a small motor component to the stapedius and muscles behind the ear. It supplies cutaneous sensation to a small area of the auricle, but stimulation here would be unlikely to trigger a vasovagal response.
(Choice C) The mandibular branch of the trigeminal nerve carries sensation from the majority of the external auditory meatus, except for the posterior wall.
(Choice E) The vestibulocochlear nerve (CN VIII) mediates hearing and vestibular proprioception. It does not mediate any cutaneous sensation.
Educational objective:
The vagus nerve provides cutaneous sensation to the posterior external auditory canal via its small auricular branch. Sensation to the rest of the canal is from the mandibular division of the trigeminal nerve.