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Malignant peripheral nerve sheath tumor at the cerebellopontine angle treated with Gamma Knife radiosurgery: case report and review of the literature.

BACKGROUND AND IMPORTANCE
Malignant peripheral nerve sheath tumor (MPNST) is a rare lesion that may arise de novo or develop from an existing benign neurofibroma. Very rarely, MPNST may develop from an existing schwannoma. Intracranial MPNST is rare, and most commonly affects thevestibulocochlear nerve. Surgery is the mainstay of treatment for these lesions, but gross total resection is often difficult given the proximity of adjacent neurovascular structures. Gamma knife radiosurgery (GKS) may represent a useful adjunct to subtotal resection or biopsy of these lesions, but its use for this tumor type has not been well defined.


CLINICAL PRESENTATION
The patient, who had a long history of progressive sub-clinical hearing loss, presented with facial droop and decreased facial sensation. Imaging revealed a large left cerebellopontine angle tumor extending into the internal auditory canal. The mass was subtotally resected, and pathology revealed a malignant peripheral nerve sheath tumor. The patient underwent fractionated external beam radiotherapy two months later to the resection cavity, followed by Gamma Knife radiosurgery (GKRS) to the residual tumor. Follow up imaging eight months after GKRS revealed a substantial reduction in tumor size. The patient has remained clinically stable.


CONCLUSION
GKS may be a useful adjunct to multimodality treatment for malignant tumors of the CPA, such as MPNST, after subtotal resection and/or radiotherapy. Close ongoing follow up with periodic MR imaging is essential to monitor for recurrence.