Medially Migrating Vestibular Schwannomas: A Review of 10 Cases.

Objective: To analyze cases of medial migration of vestibular schwannomas to propose an underlying mechanism.

Study design: Retrospective chart review.

Patients: Ten patients from one institution with sporadic vestibular schwannomas that demonstrated medial migration toward the cerebellopontine angle on serial imaging were reviewed.

Interventions: Among the 10 patients studied, 8 patients underwent stereotactic radiosurgery and 2 were managed with wait-and-scan. All serial imaging was analyzed throughout follow-up.

Main outcome measures: Volumetric and linear measurements were used to assess vestibular schwannoma growth. The fundal fluid cap length was measured from the most lateral end of the neoplasm within the internal auditory canal to the medial end of the cochlea. Pure tone averages of 0.5, 1, 2, and 3 kHz, word recognition scores, and AAO-HNS hearing class were used to assess levels of hearing loss per patient.

Results: Tumor growth exhibited a positive correlation with medial migration. Of the 10 patients studied, 9 exhibited tumor volume growth from initial to most recent imaging. Median changes in tumor volumes and fundal fluid cap lengths from initial diagnosis to the most recent imaging regardless of intervention were 130 mm 3 (range 1,400-2,970) and 2.8 mm (range 1.8-6.0), respectively. Migration was noted in 4 patients prior to any intervention, in 4 patients postradiosurgery, and in 2 patients before and after radiosurgery. Therefore, half of the tumors studied migrated before an intervention and half migrated postradiosurgery. No correlation of migration and hearing decline was observed.

Conclusion: Medial migration of vestibular schwannoma is associated with an increase in tumor volume, supporting a "tumor squeeze" mechanism within a conical internal auditory canal toward the wider porus acusticus and cerebellopontine angle.