Malignant triton tumor diagnosed twelve years after radiosurgically treated vestibular schwannoma

Stereotactic radiosurgery (SRS) has been used as the primary treatment for vestibular schwannoma (VS) over the last two decades. While literature is available on tumor response following SRS, very long-term follow-ups are not yet available. Malignant transformation of benign VS is very rare. There are only a few cases described in the literature, most of which report malignant transformation occurring between 5-10 years after radiosurgery. Here we report a case of a 65-year-old female, with no family history of neurofibromatosis, who presented with worsening mental status, gait instability and facial weakness. Twelve years prior to her presentation, she was diagnosed with a VS that was treated with stereotactic radiosurgery. The tumor had subsequently been stable on serial interval magnetic resonance imaging. She eventually presented with symptoms related to hydrocephalus and brain stem compression. Histopathologic analysis revealed a malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation. She succumbed to her disease and passed away 10 months after her resection surgery. This case highlights the necessity for lifelong follow-up following SRS and the need to be vigilant when performing SRS in large VS.