Origin, course and distribution of the nerves to the posterosuperior wall of the external acoustic meatus.

Patients with Ramsay Hunt syndrome have various clinical symptoms including vesicular rash of the external acoustic meatus and auricle. In addition to facial nerve paresis, neurological disturbances of various cranial nerves such as the acoustic nerve, glossopharyngeal nerve and vagus nerve are reported in patients of Ramsay Hunt syndrome. To understand the reasons for the clinical symptoms, we observed the nerve branches of the auricle and external acoustic meatus. We used 18 halves of 11 Japanese cadavers. All cadavers were fixed in 8% formalin and preserved in 30% ethanol. Dissection was performed under a stereomicroscope and the communication among the nerve branches was analyzed. Posterosuperior wall of the acoustic meatus was innervated by nerve branches that emerged from the tympanomastoid fissure in 17 specimens (17/18). These branches always crossed the facial canal and had more than one communicating branch with the facial nerve inside the canal (17/17) or in the petrous bone (1/17). These branches originated from the superior ganglion of the vagus. In the origin from the vagus nerve, some of these branches communicated with the glossopharyngeal nerve (3/17). In addition to these branches, the facial nerve, after originating from the stylomastoid foramen, bifurcated into two nerve branches in some specimens (7/17). Nerve branches around the external acoustic meatus and the auricle have various communications before reaching the central nervous system. The variety of communications could explain the varied symptoms of Ramsay Hunt syndrome.