Typical IAC schwannomas are intracanalicular without extension into the membranous labyrinth of the inner ear. Schwannomas may arise from any of the cranial nerves within the IAC, however, including the facial nerve (1, 5). This tumor most commonly originates near the vestibular ganglion, at the junction of the central and peripheral myelin near the fundus of the IAC. “Acoustic” schwannomas most often arise from the vestibular division of the vestibulocochlear nerve. Schwannoma is a benign neoplasm of the nerve sheath and is the most common neoplasm of the internal auditory canal (IAC) and cerebellopontine angle (1–6). Temporal bone CT is reserved for presurgical planning in the dumbbell facial nerve schwannoma group. Dumbbell schwannomas of the vestibulocochlear nerve (14/24) included transmodiolar (8/14), which extended into the cochlea, transmacular (2/14), which extended into the vestibule, and combined transmodiolar/transmacular (4/14) types.ĬONCLUSION: Simple intracanalicular schwannomas can be differentiated from transmodiolar, transmacular, and facial nerve schwannomas with postcontrast and high-resolution fast spin-echo T2-weighted MR imaging. Characteristic features included an enhancing “tail” along the labyrinthine segment of the facial nerve and enlargement of the facial nerve canal. RESULTS: Ten of 24 lesions were facial nerve dumbbell lesions. Images were evaluated for contour of the mass and extension into the membranous labyrinth or geniculate ganglion. Twenty-four patients with dumbbell lesions of the IAC had their clinical and imaging data retrospectively reviewed. METHODS: A dumbbell lesion of the IAC is defined as a mass with two bulbous segments, one in the IAC fundus and the other in the membranous labyrinth of the inner ear or the geniculate ganglion of the facial nerve canal, spanned by an isthmus. In this article, the imaging and clinical features of these dumbbell schwannomas are described. It is important to differentiate dumbbell lesions, which include facial and vestibulocochlear schwannomas, from simple intracanalicular schwannomas, as surgical techniques and prognostic implications are affected. BACKGROUND AND PURPOSE: Benign tumors of the internal auditory canal (IAC) may leave the confines of the IAC fundus and extend into inner ear structures, forming a dumbbell-shaped lesion.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |