Delayed Malignant Transformation of Petroclival Meningioma to Chondrosarcoma after Stereotactic Radiosurgery: Case Report and Review

Background: Microsurgical resection of recurrent petroclival and cerebellopontine angle meningiomas carries significant morbidity to adjacent critical neurovascular structures. Recent interest has arisen regarding stereotactic radiosurgery as a tool to prevent growth and progression of these lesions.

Case Presentation: A 58-year-old woman underwent transpetrosal, transtentorial resection of a left petroclival meningioma in 1996 at Northwestern, with a small postoperative remnant in the cavernous sinus. Pathology was consistent with grade 1 meningioma. Follow-up MR brain imaging in 1998 showed growth, prompting gamma knife radiosurgery with a dose of 14 Gy. Follow-up MRIs were stable until 2004, when she again experienced progression of this lesion. Repeat radiosurgery was performed, at a dose of 12 Gy. The lesion was subsequently stable between 2004 and 2010.

She returned in September 2011 with gait difficulties, left facial hemi-anesthesia, hearing loss, and sixth nerve palsy. An MR brain scan showed massive tumor progression with compression of the pons and spread into the middle fossa and cavernous sinus. She was taken to surgery for debulking of this lesion. Intraoperatively, it was found that the substantial portion of the lesion was grossly consistent with meningioma. However, a tough, darker segment remained partially adherent to the pons. Pathology review showed two different tissue components. One was a high-grade chondrosarcoma, with positive S-100 staining and EMA negativity. The other component was consistent with atypical meningioma.

Discussion: Recent series have shown greater than 90% rates of long-term control for posterior fossa meningiomas after stereotactic radiosurgery. Progression to anaplastic meningioma has been described in the literature and is considered a long-term risk of radiosurgical treatment. This is the first published case report of malignant transformation of meningioma to chondrosarcoma after stereotactic radiosurgery. Single case reports exist of dedifferentiation of meningioma to glioblastoma, osteosarcoma, and spindle cell sarcoma, either spontaneously or in the setting of external beam radiation.

Conclusion: Although stereotactic radiosurgery continues to gain favor as a treatment modality for recurrent posterior fossa meningioma, delayed complications remain unclear. In the setting of prior remote radiosurgery, sudden rapid progression of these lesions should be concerning for malignant progression, and dedifferentiation to sarcoma is a possibility.