Malignant haemangiopericytoma of the knee joint: MR findings.

The imaging findings of intra-articular haemangiopericytomas have not been described previously. We report on a 35-year-old man with a primary malignant haemangiopericytoma of the left knee joint. MRI demonstrated joint effusion and a heterogeneous mass with haemorrhagic components and multiple peripheral serpentine signal voids, suggesting the presence of vascular channels. Multiple pulmonary metastases were seen on chest CT. These imaging findings, although not pathognomonic, might be useful in suggesting the diagnosis of intra-articular haemangiopericytoma.