Neuropathology ReportDelayed malignant transformation of petroclival meningioma to chondrosarcoma after stereotactic radiosurgery

Stereotactic radiosurgery (SRS) is often used as adjuvant treatment for residual or recurrent tumor following microsurgical resection of posterior fossa meningiomas. SRS is associated with excellent rates of local control, however long-term complications remain unclear. Secondary malignancy is an often discussed but rarely described complication of SRS. We present a 56-year-old woman who underwent near total resection of a petroclival meningioma, followed by two episodes of SRS over the ensuing 8 years for local recurrence. She returned 14 years after initial diagnosis with neurologic deterioration and was found to have massive recurrence. Pathology was consistent with high-grade chondrosarcoma. The tumor continued to progress despite debulking and proton-beam therapy and the patient died of medical complications. To our knowledge this is the first report of malignant transformation of a meningioma to high-grade chondrosarcoma, further notable due to the remarkable clinical course and delayed presentation after initial surgery and radiosurgery. Though this may have been a de novo tumor, it is also possible that this represents a case of radiation-induced neoplasm. Although SRS continues to gain favor as a treatment modality, delayed malignant degeneration is a potential complication and physicians should counsel patients of this risk.