CT and MR imaging of intralabyrinthine schwannoma: report of two cases and review of the literature.

Abstract

Two cases of intralabyrinthine schwannoma were studied with computed tomography (CT) and magnetic resonance (MR) imaging. On CT scans, a soft-tissue mass was identified in the round window niche in both cases. Widening of the basilar turn of the cochlea and characteristic erosion of the promontory were noticed in one case. Preoperative MR imaging (performed in only one case) revealed a soft-tissue mass in the labyrnth, extending into the round window niche. Findings at CT and MR imaging are discussed, and a differential diagnosis is given. The literature is reviewed. The authors' findings suggest that CT and MR imaging may prove very valuable in the previously difficult preoperative diagnosis of these tumors. In the setting of progressive sensorineural hearing loss, atypical Meniere disease, or recurrent vertigo, the presence of a mass in the labyrinth or labyrinthine windows- delineated on CT or MR images, despite a normal internal auditory canal, cerebellopontine angle, or brain stem - is highly suggestive of intralabyrinthine schwannoma.

Intralabyrinthine Schwannomas: Imaging Diagnosis and Classification

“…Previous reports have proposed that the location on imaging may predict the symptoms. 10,[19][20][21] In earlier reports, it was suggested that tumors confined to the vestibule more commonly cause vertigo or symptoms similar to Meniere disease. 12,19,23 However, in our series, tumor location had no reproducible bearing on symptoms.…”

“…In 1990, the first cases of ILS were globally described on enhanced MR imaging as homogeneous enhancement in the labyrinth. 10,27 Following this, several reports used enhanced MR imaging as a primary diagnostic tool for ILS. 12,14,16,17,22,23,26 More advanced imaging and characterization with high-resolution T2 and gradient recalled-echo sequences appeared in the literature in the early 2000s.…”

“…1,21,[28][29][30][31] Some reports have suggested that the lesions can be invisible on T2 and even postgadolinium T1-weighted images. 10,17,26 This insensitivity may have been due to section thickness and less optimized imaging sequences at that time. In all of our cases, these lesions were visualized on both sequences.…”

“…This tumor most commonly originates near the vestibular ganglion at the junction of the central and peripheral myelin near the fundus of the IAC at the Schwann cellϪglial junction but can be found anywhere along the nerve from the IAC to the terminal ends of the eighth cranial nerve within the vestibule, cochlea, or semicircular canals. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] ILSs are defined as tumors arising primarily from within the membranous labyrinth: cochlea, vestibule, or semicircular canals.…”

Imaging of Intralabyrinthine Schwannomas: A Retrospective Study of 52 Cases with Emphasis on Lesion Growth

“…3,4 Diagnosis of ILSs was difficult on CT, and only isolated cases were described. 5,6 With the advent of gadolinium (Gd)-enhanced MR imaging, an increasing number of ILSs were detected during screening for hearing loss and/or vertigo. 7 The use of heavily T2-weighted images for the detection of these lesions was reported a few years later.…”