Schwannomas do not produce facial weakness until the tumors are very large. Radiologic diagnosis Just as with CT, MRI of facial neuroma produces imaging characteristics identical to those of ANs. When these tumors involve the temporal bone by erosion they are easy to diagnose by imaging. However the distinction preoperatively of an internal auditory canal tumor of the facial nerve versus an acoustic neuroma is most difficult. The only clues to such a situation are preoperative facial nerve symptoms which should raise this possibility.
Trigeminal neuromas are the next most common type of intracranial neuroma.
Schwannomas of the CNs IX, X, XI, and XII are distinguished by their location and pattern of expansion as well as the symptoms they produce. Trigeminal neuromas arise both intradurally, from the nerve root in the CPA and Meckel's cave, and extradurally, from the gasserian ganglion in the middle cranial fossa. Neuromas of CN IX, X, and XI produce smooth enlargement of the jugular foramen and classically produce hypesthesia and weakness of the palate, vocal cord, and shoulder, respectively. Lalwani, A.K., Meningiomas, epidermoids, and other nonacoustic tumors of the cerebellopontine angle. Otolaryngologic Clinics of North America, 1992.