Twelve Years Delayed Malignant Transformation of a Vestibular Schwannoma after Radiosurgery

Malignant transformation of a previously histologically proven benign vestibular schwannoma is very rare. There are only few cases described in the literature with malignant transformation, which have occurred between 5 and 10 years after initial diagnosis. We report a case of 65-year-old woman, with no family history of neurofibromatosis type 2, who presented with worsening mental status, gait instability, and facial weakness. Twelve years prior to her presentation, she was diagnosed with a vestibular schwannoma that was treated with radiosurgery that had remained stable upon follow-up with serial MRIs. Imaging obtained at admission demonstrated ventriculomegaly and a 300% increase in tumor volume with significant local mass effect. A near total resection was performed. Histopathologic analysis revealed malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation known as a malignant triton tumor (MTT). MTT represents a more aggressive phenotype of malignant peripheral nerve sheath tumor.Postoperatively, patient’s confusion improved but she had persistent cranial nerve deficits. She also developed leptomeningeal enhancement along the thoracolumbar meninges suggesting drop metastasis. She underwent palliative radiation. She subsequently succumbed to her disease approximately 2 months later.

Multiple factors should be considered when managing patients with vestibular schwannoma. This abstract emphasizes the concern of malignant transformation of vestibular schwannoma following radiation.