A patient with herpes zoster oticus shows clusters of vesicles on the concha, in the small depression anterosuperior to the external acoustic meatus, and on the outer surface of the tympanic membrane. Which two nerves account for this cutaneous distribution of the external ear?

The auriculotemporal nerve (V3) and the auricular branch of the vagus nerve (Arnold's nerve) together account for the concha, the suprameatal depression and the outer tympanic membrane surface because these are the two nerves whose cutaneous territories precisely overlap the vesicular distribution described.

Why the auriculotemporal and vagus nerves are the only pair that fits

The question describes three specific sites of vesiculation: the concha, the small depression anterosuperior to the external acoustic meatus (the suprameatal triangle, also called Macewen's triangle), and the outer surface of the tympanic membrane. No single nerve covers all three. The auriculotemporal nerve, a branch of the mandibular division of the trigeminal nerve, supplies the tragus, the anterior portion of the helix, and the anteroinferior wall of the external auditory canal as far as the tympanic membrane. The auricular branch of the vagus nerve, also known as Arnold's nerve, arises from the superior ganglion of the vagus, passes behind the internal jugular vein, enters the mastoid canaliculus, and crosses the facial canal about 4 mm above the stylomastoid foramen before reaching the surface through the tympanomastoid fissure. It supplies the concha, the posterosuperior wall of the external auditory canal, and the outer surface of the tympanic membrane. The suprameatal triangle lies within the territory where these two nerves meet. Only option A names both nerves. Every other option either omits one of these two or substitutes a nerve that does not reach the concha or the tympanic membrane.

The facial nerve contributes sensory fibers to the concha via the nervus intermedius, but these fibers travel with the auricular branch of the vagus and with the auriculotemporal nerve rather than reaching the skin independently. The glossopharyngeal nerve sends its tympanic branch, Jacobson's nerve, through the tympanic canaliculus to form the tympanic plexus on the promontory, but this plexus supplies the inner surface of the tympanic membrane and the mucosal lining of the middle ear, not the outer cutaneous surface. Therefore neither CN VII nor CN IX directly accounts for the cutaneous distribution described, which is why option C is wrong despite the known role of the geniculate ganglion in herpes zoster oticus.

The complete sensory map of the external ear and its boundaries

The external ear receives sensory innervation from four cranial nerves and two cervical plexus branches, and the boundaries between their territories are clinically important because they determine where vesicles, anaesthesia or referred pain will appear.

Sensory territories of the external ear

The suprameatal triangle is the depression bounded by the posterosuperior margin of the external acoustic meatus, the supramastoid crest, and a tangent line from the posterior canal margin to the crest. It lies directly lateral to the mastoid antrum and is the site where Arnold's nerve reaches the skin. The concha is almost entirely vagal in its sensory supply, which is why stimulation of the external auditory canal during syringing can produce a vagal reflex causing bradycardia or cough, the ear-cough reflex mediated by Arnold's nerve.

Herpes zoster oticus and the geniculate ganglion

Herpes zoster oticus, also called Ramsay Hunt syndrome type II, results from reactivation of latent varicella zoster virus in the geniculate ganglion of the facial nerve. The syndrome classically presents with a triad: painful vesicles on the external ear, ipsilateral facial palsy, and vestibulocochlear dysfunction (tinnitus, vertigo, sensorineural hearing loss). The vesicles appear in the sensory distribution of the nerves that carry fibers from or near the geniculate ganglion. The nervus intermedius, the sensory and parasympathetic root of the facial nerve, joins the main facial nerve at the geniculate ganglion and contributes sensory fibers that travel with the auricular branch of the vagus and with the auriculotemporal nerve to reach the concha and the external auditory canal. This is why the vesicles of herpes zoster oticus appear on the concha and the outer tympanic membrane even though the virus is latent in the facial nerve ganglion. The auriculotemporal nerve is involved because the nervus intermedius communicates with the otic ganglion and through it with V3 branches. The glossopharyngeal nerve is involved in the syndrome only insofar as Jacobson's nerve contributes to the tympanic plexus and may carry pain fibers from the inner tympanic membrane, but it does not supply the outer surface where the vesicles are seen.

The distinction between Ramsay Hunt syndrome and Bell's palsy is clinically important because Ramsay Hunt carries a worse prognosis for facial nerve recovery, with only about 50 to 70 percent achieving complete recovery compared with over 80 percent in Bell's palsy. Antiviral therapy with acyclovir or valacyclovir combined with corticosteroids is the standard treatment, and early initiation within 72 hours of rash onset improves outcomes.

How ear innervation questions are framed in postgraduate exams

Questions on external ear innervation appear in NEET PG, INI-CET and FMGE in three recurring patterns. The first pattern, as in this question, gives a clinical scenario with vesicles or anaesthesia at specific sites and asks which nerves supply those sites. The second pattern asks about the nerve responsible for a specific reflex, most commonly the ear-cough reflex (Arnold's nerve, CN X) or the referred otalgia pathways (CN V3, CN VII, CN IX, CN X, C2, C3). The third pattern tests the relationship between a cranial nerve lesion and the resulting sensory deficit on the ear, for example asking which nerve lesion causes loss of sensation over the concha.

Students frequently confuse the inner and outer surfaces of the tympanic membrane. The outer surface is supplied by the auriculotemporal nerve anteriorly and Arnold's nerve posteriorly. The inner surface is supplied by Jacobson's nerve, the tympanic branch of CN IX. A question that mentions vesicles on the outer surface is testing the cutaneous supply, not the mucosal supply. Another common error is to assume that because the facial nerve is the nerve affected in Ramsay Hunt syndrome, it must directly supply the skin where vesicles appear. The facial nerve's role is indirect, via the nervus intermedius and its communications with the vagus and trigeminal systems.

The great auricular nerve and lesser occipital nerve are frequently offered as distractors because they are the most commonly memorized nerves of the ear. They supply the skin behind the ear and the lower lateral auricle, not the concha or the meatus. The posterior auricular nerve, a branch of the facial nerve, supplies a small area on the medial surface of the auricle above the lobule and is not relevant to the concha or tympanic membrane.

Why the other options fail

One-glance recall table

What the exam actually asks

• Memorize the three sites supplied by Arnold's nerve: concha, posterosuperior EAC wall, outer TM surface. These are the sites of vesicles in Ramsay Hunt syndrome.
• The ear-cough reflex is mediated by the auricular branch of the vagus. Any question mentioning cough or bradycardia on ear stimulation points to CN X.
• Referred otalgia pathways are tested by giving a primary lesion site and asking where pain is felt. CN V3 lesions refer to the tragus and anterior canal. CN IX and CN IX lesions refer to the concha and deep ear. C2 and C3 lesions refer to the lower auricle and mastoid.
• The outer tympanic membrane is cutaneous (V3 and CN X). The inner tympanic membrane is mucosal (CN IX). Questions that specify vesicles on the outer surface are testing cutaneous innervation.
• The suprameatal triangle is the clinical landmark for the mastoid antrum and for the point where Arnold's nerve reaches the skin. It is the depression anterosuperior to the external acoustic meatus.

Traps that cost marks

• Selecting the facial nerve as a direct cutaneous supplier because Ramsay Hunt syndrome involves the geniculate ganglion. The facial nerve's sensory fibers reach the skin only via the nervus intermedius traveling with Arnold's nerve and the auriculotemporal nerve.
• Choosing the glossopharyngeal nerve because Jacobson's nerve is associated with the tympanic membrane. Jacobson's nerve supplies the inner mucosal surface, not the outer cutaneous surface where vesicles appear.
• Assuming the great auricular nerve supplies the entire lateral surface of the auricle. It supplies only the lower portion; the upper lateral surface is supplied by the lesser occipital nerve and the auriculotemporal nerve.
• Confusing the zygomaticotemporal nerve (V2, temple) with the auriculotemporal nerve (V3, tragus and anterior canal). The names are similar but the territories are different.

Frequently asked

Why does herpes zoster oticus cause vesicles on the concha if the virus is in the facial nerve?

The varicella zoster virus reactivates in the geniculate ganglion of the facial nerve, but the sensory fibers that reach the concha travel with the nervus intermedius, which communicates with the auricular branch of the vagus nerve and with the auriculotemporal nerve. These peripheral branches carry the virus to the skin, producing vesicles in their cutaneous territories even though the ganglion of latency is the geniculate ganglion.

What is the difference between the inner and outer surface innervation of the tympanic membrane?

The outer surface of the tympanic membrane is cutaneous and is supplied by the auriculotemporal nerve anteriorly and the auricular branch of the vagus posteriorly. The inner surface is mucosal and is supplied by Jacobson's nerve, the tympanic branch of the glossopharyngeal nerve, which forms the tympanic plexus on the promontory. Questions about vesicles on the outer surface test the cutaneous supply, not the mucosal supply.

Which nerve is responsible for the ear-cough reflex and why is it clinically relevant?

The auricular branch of the vagus nerve, Arnold's nerve, mediates the ear-cough reflex. Stimulation of the posterosuperior wall of the external auditory canal, which is supplied by Arnold's nerve, can trigger a vagal reflex causing cough, bradycardia or even syncope. This is clinically relevant during ear syringing or otoscopic examination, and it explains why patients with cerumen impaction in the posterior canal may cough during removal.

References

• Gray's Anatomy, 42nd. chapter on external ear and cranial nerve branches
• Harrison's Principles of Internal Medicine, 21st. herpes zoster and varicella zoster virus infections
• Bailey and Love's Short Practice of Surgery, 28th. ear anatomy and Ramsay Hunt syndrome