51 year old lady presented with headache and gait disturbances. An MRI including perfusion imaging was obtained. MRI revealed an extra-axial, dural based mass of the posterior fossa which was isointense to gray matter on T1 weighted sequence and hyperintense to gray matter on T2 weighted sequence. There was no diffusion restriction. On T2 weighted sequence, there was wedge shaped area of perilesional T2 hyperintensity extending transversely and superiorly to involve vermis. With contrast, the lesion showed intense homogenous enhancement. On perfusion study, there was considerable increase in rCBV. Preoperatively it was diagnosed as meningioma and the patient was scheduled for resection.
On surgery, the mass was encapsulated but the capsule was tightly adherent to the cerebellum. On histopathology, the tumor turned out to be a malignant fibrous histiocytoma (MFH) with 40% MIB-1 index.
MFH, the most common soft tissue sarcoma in adults, arises from fibroblasts, myofibroblasts or undifferentiated mesenchymal cells. Most patients are between 50 and 70 years old. Men are affected 2-3 times more commonly than women. Most MFHs arise de novo however, they can occur secondary to prior radiation, trauma, Paget’s disease, chronic osteomyelitis or benign bone tumors. MFH most commonly occurs in lower extremity. Head and neck area is involved up to 10% of cases. In head neck, nasal cavity and paranasal sinuses are most commonly involved. It has variable appearances on CT and MRI. On CT, this is usually large lobulated sift tissue mass which is isodense to muscles with destruction/remodeling of adjacent bone. There may calcification in up to 5-20% of patients. On MRI, they are isointense to muscle on T1 weighted sequence and heterogeneously hyperintense on T2 weighted sequence. This tumor can have both solid and cystic component. Solid portion enhances intensely. Spontaneous hemorrhage is frequently seen and can obscure the primary tumor. The diagnosis is important because it is a malignant tumor and post-resection radiation therapy is required for better tumor control. MFH also has poor prognosis.
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