AN ANATOMICAL STUDY OF THE TYMPANIC BRANCH OF THE GLOSSOPHARYNGEAL NERVE (NERVE OF JACOBSON)

Our study was aimed to examine the anatomic relationships of the tympa nic branch of the glossopharyngeal nerve (GPN), namely the Jacobson's nerve (JN). The JN is the first branch of the GPN after having passed the jugular foramen. It contributes to the tympanic plexus on the prom ontory. It transmits secretory innervation to the parotid gland. Its p ossible role in the regulation of the middle ear pressure has also bee n hypothesized in terms of animal studies. Using microdissection techn iques and high-resolution computed tomography (HRCT) scanning, the ana tomic relationships and course of the JN were examined in eight formal in-preserved cadavers(16 sides). A morphometric analysis related to th e JN was also performed both in the 16 cadavers and 40 dry-skull speci mens. The JN emerged from the inferior ganglion of the GPN in all spec imens. The mean distance between the ganglion and the genu of the GPN was 11.3 mm. The inferior 2/3 of the tympanic canal (TC) followed a ve rtical course, and then it ran anteromedially with an angle of 160 deg rees to 170 degrees. The mean length of the TC was 9.5 mm. The TC was well-defined in all axial HRCT scans. In 2 cases the JN was entirely e ncased in a bony canal in the middle ear. A double JN was observed in one case. This study gives an additional information regarding the ana tomy of the JN.