[Origin of acoustic neuroma].

Acoustic neurinomas are vestibular schwannomas. Ultramicroscopic examination of the root of these tumors, removed using a petrosal approach (translabyrinthic, suprapetrosal) in 20 cases, investigated the site of origin of the schwannoma. Tumoral capsule was absent between Scarpa's ganglion cells and tumoral cells, these two types of cells being intermingled. The fact that the very small tumors, 3 to 5 mm in diameter, were all derived from Scarpa's ganglion and were separated by a capsule from the other structures of internal auditory canal prove that acoustic neurinoma arises from Scarpa's vestibular ganglion. Other studies have shown the absence of myelin surrounding bodies of Scarpa's ganglion cells in humans, inversely to findings in other vertebrates. Since on the one hand the appearance in humans is similar to that observed during development of Scarpa's ganglion in the rat, and on the other hand acoustic neurinoma has never been demonstrated in the animal, it can be suggested that acoustic neurinoma development in humans corresponds to cellular immaturity of Scarpa's ganglion.