Labyrinthine Fluid Signal Intensity on T2-Weighted MR Imaging in Patients With Vestibular Schwannomas Undergoing Proton Radiotherapy: A Longitudinal Assessment.

OBJECTIVE: In vestibular schwannoma patients, a loss of signal intensity (SI) on T2-weighted magnetic resonance imaging (MRI) has been reported within the ipsilateral labyrinth. The purpose of this study was to quantitatively evaluate the occurrence and course of this intensity loss in relation to proton radiotherapy and its possible association with hearing loss. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary referral center. PATIENTS: Patients who received proton therapy for a vestibular schwannoma and underwent at least two high-resolution T2-weighted cisternographic sequence (constructive interference in steady state/fast imaging employing steady-state acquisition/DRIVE) MRIs and audiometry assessments. MAIN OUTCOME MEASURES: Relative T2 SIs from the vestibules and basal/apical cochlear turns of the labyrinth, bilaterally. RESULTS: Ninety-five MRI scans from 34 patients were included. The apical turn of the ipsilateral cochlea showed a lower mean cochlear SI than on the contralateral side (±3.5 versus 5.0). The mean relative cochlear SI did not significantly change after proton radiotherapy. The ipsilateral vestibule showed a higher SI than the cochlea. The relative mean cochlear SI was not directly correlated to (the degree of) hearing loss before or after proton radiotherapy, nor did it predict future hearing loss. CONCLUSION: The relative mean cochlear SI on cisternographic T2-MRI in vestibular schwannoma patients is diminished on the treated side, when compared with the ipsilateral vestibule and the contralateral cochlea/vestibule. The SI of the ipsilateral cochlea does not further decrease after proton radiotherapy and seems to be related to the tumor rather than the therapy. The diminished cochlear SI does not correlate with subsequent loss of hearing.

Quantitative assessment of perilymph sources.

The problem of the perilymph origin--influx of cerebrospinal fluid (CSF) versus ultrafiltration within the cochlea--cannot be solved by mere qualitative proofs of tracer passage through the cochlear aqueduct. In order to gain quantitative data on the possible perilymph sources, an experimental study was designed to follow the time course of dye concentrations in the cisternal CSF and in the perilymph after tracer injection into the CSF at the vertex. By comparing the resulting concentration peaks in both fluids, the mean peak of the perilymph tracer concentrations was found to reach 36% of the maximum CSF concentration only. It is concluded that the local perilymph production within the cochlea exceeds the influx of CSF by a ratio of about 2:1. A working hypothesis of the double perilymph origin is discussed.