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Characteristics of Intralabyrinthine Schwannoma

July 14, 2009
Written by: , Filed in: Neuroradiology
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Intralabyrinthine schwannomas (ILSs) are rare lesions that develop along branches of the vestibulocochlear nerve within the temporal bony labyrinth but not within the internal auditory canal (IAC). They enhance brightly on T1-weighted images.

The main differential diagnosis is labyrinthitis, which is usually more diffuse, less well defined, and eventually resolves.

Low signal areas on T2 within the labyrinth can be due to fibrosis or calcification following chronic labyrinthitis. These lesions can grow and eventually require surgery.

The objective of a reccent retrospective study was to describe the MRI findings, clinical presentation, and characteristics of growth of ILSs. The study was comprised of 52 patients with ILS over a period of 16 years.

The study concluded that ILSs occur most frequently in the cochlea and grow in >50% of patients; 11.1 % may extend into the IAC on follow-up, but usually after filling at least most of the cochlea.

Methodology
Depending on the scanner used, slice thickness was between 0.5 and 0.8 mm on T2 images and between 1 and 3 mm on post-gadolinium T1. Lesions were only included if they enhanced strongly with sharply delineated edges on T1 and T2 images. Tumors with a component within the IAC were excluded.

Results of the Study
Lesions were dark on T2 images relative to the surrounding fluid. Of the 59 lesions, 42 (80.7%) were initially intracochlear, most commonly in the basal and second turn.

Of these 42, 26 were in scala tympani alone and the remainder involved scala tympani and vestibuli, suggesting that they originate in the scala tympani.

Seven lesions (13.5%) were intravestibular, only 2 of which were only in the semicircular canals.

Three lesions (5.8%) were in the vestibule and cochlea. Of the 8 lesions in the vestibule, the anterior part was always involved.

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review

Follow-up studies were available in 27 patients, and the lesions grew in 16 (59.3%) of these, 11 of which were within the cochlea. Three of these progressed into the IAC (11.1%) after nearly filling the entire cochlea.

None of the vestibular lesions grew into the IAC. Clinical data were available in 49 patients; 48 presented with sensorineural hearing loss, which was sudden in 7.

Ten patients experienced vertigo, which was the initial symptom in 3 and acute in 2. Twenty-nine patients experienced pulsatile (n=21) or nonpulsatile (n=8) tinnitus.

Surgery was performed in 12 patients and sacrificed any residual hearing. Tinnitus remained in 8 of ten patients and vertigo in 5 of 6 patients. Three patients developed gustatory problems.

Conclusions
ILS occurs most frequently in the cochlea and grows in >50% of patients. 11.1 % may extend into the IAC on follow-up, but usually after filling at least most of the cochlea.

Surgical removal of ILS is only indicated for fear of facial nerve involvement in the IAC and should be limited to those patients in which there is imminent or actual IAC invasion.

Reviewer’s Comments
The data on these cases with follow-up was instructive, and suggests that ILS should be followed out of concern for IAC invasion, which occurs in 11% of cases. However, this usually occurs after involvement of most of the cochlea.

Author: Yaron Lebovitz, MD)

Reference:
Tieleman A, Casselman JW, et al. Imaging of Intralabyrinthine Schwannomas: A Retrospective Study of 52 Cases With Emphasis on Lesion Growth. AJNR; 2008; 29 (May): 898-905

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review
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