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Nervus intermedius neuralgia sometimes known as or Geniculate Neuralgia is an extremely uncommon pain syndrome in which the patient reports shock-like pains in the distribution of the nervus intermedius, which is the somatic sensory branch of cranial nerve VII. The pain is in every way similar to that of tic douloureux except for its location. Few cases have been reported since the origin report by Clark and Taylor in 1909.
It is presumed that the etiology of nervus intermedius tic is analogous to that of trigeminal tic: cross compression of the nerve at its central-peripheral myelin junction, a few millimeters from the lateral pons. Jannetta described such a finding and the beneficial results produced by moving the offending vessel.
Symptoms and Signs
The patient complains of intermittent stabbing pain, like electric shock, deep in the ear. The pain can be triggered by non-noxious stimulation of the ear canal or can follow swallowing or talking. The patient is pain free between attacks. Neurologic deficits are absent. The syndrome is always unilateral. Some patients have reported, salivation, bitter taste, tinnitus, and vertigo during the pain attacks; perhaps this indicates involvement of central connections of the nervus intermedius or irritation of other components of cranial nerves VII and VIII. Rarely, patients with pain in the trigeminal distribution also have pain in the nervus intermedius territory.
Geniculate neuralgia can also be caused by herpes zoster. The patient with geniculate neuralgia usually has vesicular eruption on the eardrum and external canal that follows the onset of the pain by 1 or 2 days. The pain is constant and burning and can be readily discriminated from the intermittent stabbing pain of nervus intermedius tic.
The medical management of nervus intermedius neuralgia is identical to that of tic douloureux. When medications do not control the pain, a surgical procedure is warranted. It is impossible to block the nervus intermedius with local anesthetics, but they can be injected into the glossopharyngeal or trigeminal nerve to establish the fact that these two nerves are not responsible for the pain, leaving, by subtraction, the nervus intermedius as the culprit.
When medical management fails, suboccipital craniectomy with exploration of the nervus intermedius is indicated. If an offending vessel is found, it can be mobilized. If no vessel can be identified, the nervus intermedius should be sectioned. This procedure is highly likely to relieve the pain permanently, but when it does not, section of the medial aspect of the descending trigeminal tract is indicated.
Additional Remarks from FNR Editors
Gamma Knife surgery is a possible treatment for geniculate neuralgia. Some neurosurgeons when asked do not recommend the procedure but have given no explanations as to why not.
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