Cirsoid aneurysm of the synovium of knee: a very rare pathology.

A 10-year-old male presented with pain and restriction of movements of left knee for 6 months. A lesion with hyperintensity on T2 weighted images was demonstrated in the anterior aspect of the left knee. Patient was treated with arthroscopic removal of the lesion which later on proved to be cirsoid aneurysm of the synovium. We could not find any other report of a "cirsoid aneurysm" in the synovium of a joint in the English literature. This case is probably the first report of cirsoid aneurysm in the synovium of a joint.