Dedifferentiation of an intracranial leptomeningeal solitary fibrous tumor to a rhabdomyosarcoma

Solitary fibrous tumors are fibroblastic mesenchymal neoplasms that also include what was previously known as hemangiopericytoma. Dedifferentiation of solitary fibrous tumors is rare and usually manifests as a high-grade sarcoma. We report a case of dedifferentiation of an intracranial leptomeningeal solitary fibrous tumor to a rhabdomyosarcoma in a 65-year-old female. The initial biopsy demonstrated a purely STAT6 positive leptomeningeal anaplastic hemangiopericytoma overlying the occipital lobe with no evidence of a rhabdomyosarcomatous component. Four years later, a biopsy of the recurrent tumor contained both solitary fibrous tumor and rhabdomyosarcoma elements intertwined. The following year at autopsy, only a rhabdomyosarcoma remained. The rhabdomyosarcoma grew predominately in a leptomeningeal pattern as did the antecedent solitary fibrous tumor, however, the autopsy also showed invasion of the brain parenchyma via the Virchow-Robin spaces indicative of increased aggressive behavior. Solitary fibrous tumors and their counterpart, hemangiopericytoma, are generally considered stable neoplasms with a characteristic STAT6 mutation. However, they may rarely undergo dedifferentiation to high grade sarcomas with a variety of morphologies including rhabdomyosarcoma. Our case is unique given the tumor’s leptomeningeal location and its differentiation to rhabdomyosarcoma lacking any solitary fibrous tumor component