PEER-REVIEW REPORTS The Nervus Intermedius: A Review of Its Anatomy, Function, Pathology, and Role in Neurosurgery R. Shane Tubbs1, Dominik T. Steck1, Martin M. Mortazavi1, Aaron A. Cohen-Gadol2 PAIN Key words Ⅲ BACKGROUND: Geniculate neuralgia, although uncommon, can be a debili- Ⅲ Anterior inferior cerebellar artery tating pathology. Unfortunately, a thorough review of this pain syndrome and the Ⅲ Cranial nerve Ⅲ Facial nerve clinical anatomy, function, and pathology of its most commonly associated nerve, Ⅲ Intermediate nerve the nervus intermedius, is lacking in the literature. Therefore, the present study Ⅲ Microvascular decompression aimed to further elucidate the diagnosis of this pain syndrome and its surgical Ⅲ Neuralgia treatment based on a review of the literature. Ⅲ Nervus intermedius Ⅲ Vestibulocochlear nerve Ⅲ METHODS: Using standard search engines, the literature was evaluated for Ⅲ Wrisberg nerve germane reports regarding the nervus intermedius and associated pathology. A summary of this body of literature is presented. Abbreviation and Acronym MRI: Magnetic resonance imaging Ⅲ RESULTS: Since 1968, only approximately 50 peer-reviewed reports have been published regarding the nervus intermedius. Most of these are single-case From 1Pediatric Neurosurgery, Children’s Hospital, Birmingham, Alabama; and reports and in reference to geniculate neuralgia. No report was a review of the 2Goodman Campbell Brain and Spine, Department of literature. Neurological Surgery, Indiana University, Indianapolis, Indiana, USA Ⅲ CONCLUSIONS: Neuralgia involving the nervus intermedius is uncommon, but To whom correspondence should be addressed: when present, can be life altering. Microvascular decompression may be Aaron A. Cohen-Gadol, M.D., M.Sc. effective as a treatment. Along its cisternal course, the nerve may be difficult to [E-mail: [email protected]] distinguish from the facial nerve. Based on case reports and small series, Citation: World Neurosurg. (2013) 79, 5/6:763-767. http://dx.doi.org/10.1016/j.wneu.2012.03.023 long-term pain control can be seen after nerve sectioning or microvascular Journal homepage: www.WORLDNEUROSURGERY.org decompression, but no prospective studies exist. Such studies are now neces- Available online: www.sciencedirect.com sary to shed light on the efficacy of surgical treatment of nervus intermedius 1878-8750/$ - see front matter © 2013 Elsevier Inc. neuralgia. All rights reserved. INTRODUCTION ANATOMY AND FUNCTIONS which is often crescent shaped, of the ner- The nervus intermedius was first identified The nervus intermedius consists of fibers vus intermedius to the vestibulocochlear in 1563, and it was Heinrich August Wris- derived from the superior salivary nucleus nerve has been found to be approximately 8 berg who named it the “portio media inter whose stimulation results in secretion of mm (11, 20). Inside the meatus, the motor comunicantem faciei et nervum auditorium” in the lacrimal and submandibular and sub- root of the facial nerve and the nervus inter- 1777 (1). This nerve (Figure 1), often re- lingual glands (4). Traveling along this medius are usually bound together as a sin- ferred to as the Wrisberg nerve, carries nerve are sensory fibers derived from the gle structure. parasympathetic fibers to the lacrimal and gustatory receptors destined for the supe- In the temporal bone, the facial nerve nasopalatine glands and transmits sensory rior pole of the solitary nucleus in the me- continues its course through the facial ca- information from the tongue and various dulla and fibers for cutaneous sensation of nal. The nerve is supplied from branches of skin areas of the nose and concha of the parts of the ear destined for the dorsal part the middle meningeal, maxillary, and pos- ear (8, 20, 22, 28). A cutaneous branch of the trigeminal tract (31). The course of terior auricular arteries. Between the co- arises near the origin of the chorda tym- the nervus intermedius and the motor root chlea and the semicircular canals, it runs pani nerve and joins with the auricular of the facial nerve can be divided into cister- laterally above the vestibule. Reaching the branch of the vagus nerve to supply the nal, meatal, labyrinthal, and extracranial medial wall of the epitympanic recess, the external auditory canal and concha of the parts. Rhoton et al. (20) found that, on av- geniculum (external genu) is formed. This external ear. It is this innervation that al- erage, the length of all 3 segments was 22 point, above the base of the cochlea, is the lows herpetic vesicles to be identified in mm. The nerve takes its name from its in- location of the geniculate ganglion (14). the ear with viral infection of the genicu- termediate position between the facial and Here the nerve gives rise to the greater late ganglion, the so-called Ramsay-Hunt superior portion of the vestibular nerves petrosal nerve (greater superficial petrosal syndrome (20). (20). The average length of adherence, nerve), which carries parasympathetic fi- WORLD NEUROSURGERY 79 [5/6]: 763-767, MAY/JUNE 2013 www.WORLDNEUROSURGERY.org 763 PEER-REVIEW REPORTS R. SHANE TUBBS ET AL. THE NERVUS INTERMEDIUS Section of the nervus intermedius may two of them for more than 10 years. The decrease the cutaneous sensitivity in the first patient, a 43-year-old woman, suf- area around the concha of the external ear, fered from attacks of right-sided face and sensation from anterior nasopharynx and head pain for 7 years that later became tympanic membrane, part of the external associated with severe pain in the right auditory canal, and the area behind the ear PAIN ear. During surgery and under local anes- and over the mastoid process (11, 22). Stim- thesia, the facial, vestibulocochlear, and ulation of the nervus intermedius can cause glossopharyngeal nerves, including the referred pain to the ear, and the projection nervus intermedius, were explored; stim- of fibers from this nerve might also explain ulation of the nervus intermedius resulted referred pain to the face after irritation of in pain in the ear and right face. The same the nervus intermedius (20). Therefore, the symptoms could be produced when stim- Figure 1. Cadaveric dissection of the right nervus intermedius plays an important role ulating the vestibulocochlear nerve. The porus acousticus noting the facial, nervus in the surgical treatment of neuralgia of the facial (inadvertently) and vestibuloco- intermedius, and vestibulocochlear nerves. external auditory canal (see later) (20). In- chlear nerves and the nervus intermedius terestingly, Ashram et al. (6) described elec- were sectioned. No recurrence was noted tromyography activity in the orbicularis oris at 15 years of follow up. The second pa- bers supplying the lacrimal, nasal, and pal- muscle after stimulation of the nervus inter- tient, a 56-year-old man with attacks of atine glands (22, 29). The tympanic cavity medius. left-sided facial pain that were associated and the nerve are separated only by a thin Burmeister et al. (8) conducted a study in with ipsilateral lacrimation and nasal layer of bone and this layer might be absent, which they tried to identify the nervus inter- congestion, underwent left greater petro- so in some individuals, there is only the mu- medius with 3-T magnetic resonance imag- sal neurectomy, which brought relief for 3 cosa between the nerve and the cavity of the ing (MRI). Their conclusion was that the years. A third patient, a 65-year-old man middle ear, and therefore the nerve might nervus intermedius can be depicted reliably who suffered from attacks of pain on the be easily affected by infections of the middle with MRI, which might be helpful, espe- left side of the face without lacrimation, ear. Possible anomalies include the nerve cially in the diagnosis of the source of tu- nasal congestion, or ear pain, also under- lying in the wall of the mastoid antrum with mors in this region. went sectioning of the nervus interme- the nerve emerging from the mastoid pro- dius. Lacrimation was lost, but no loss of cess and division of the nerve within the taste occurred, and the patient became facial canal (branches leave the temporal GENICULATE NEURALGIA AND ITS pain-free postoperatively. The fourth pa- bone through different foramina in this SURGICAL TREATMENT tient, a 36-year-old man, complained of case). An anterolateral turn toward the pa- Although nervus intermedius (geniculate) daily headaches for 6 to 8 weeks per year. rotid gland describes the extracranial neuralgia is rare and difficult to diagnose, a The pain was in the right cheek, eye, fore- course of the facial nerve after it emerges number of different surgical treatment op- head, temple, and behind the right ear. In from the stylomastoid foramen (14, 31). tions have evolved, leading to more confu- this case, a large internal auditory artery Rhoton et al. (20) and Oh et al. (16) found sion about the most appropriate approach. was seen between the facial and vestibu- up to 4 to 5 roots that made up the nervus The International Headache Society (10) de- locochlear nerves. Sectioning of the ner- intermedius, although a single root was the fines nervus intermedius neuralgia as inter- vus intermedius caused decrease of lacri- most common. Additionally, Rhoton et al. mittent episodes of pain located deep in the mation and loss of taste on the anterior (20) stated that in approximately 20% of ear that last for seconds or minutes; the two-thirds of the tongue and immediate cases, it is impossible to identify the nervus posterior wall of the auditory canal may be a relief of pain (24). There is some variation intermedius along its intracisternal course trigger zone. The pain can be accompanied in the distribution of pain among the because it is intimately attached to the ves- by disorders of lacrimation, salivation, and above patients (some suffering from fa- tibular part of the vestibulocochlear nerve taste (10). In 1909, Clark and Taylor (9) were cial pain) making it difficult to assess who and does not separate from it until the inter- the first to report success in treating facial reliably harbored geniculate neuralgia.