We believe these histopathologic features are those of a benign juxta-articular myxoma. The age, sex and location of this lesion are fully compatible with this diagnosis. This lesion is utterly benign yet may recur in a minority of cases. It is perhaps related to ganglion cyst.
Contributor's Note: The diagnosis of a juxta-articular myxoma (JAM) should be considered in male patients presenting with a painful knee mass, particularly with a history of previous trauma to the knee. The majority of lesions occur in the sucutaneous adipose tissue and develop cystic spaces resembling ganglion cysts. Although cytologic features including intracellular mucin droplets may mimic lipoblastic activity, JAM is distinguished from myxoid liposarcoma by the absence of oil red O-positive material and characteristic delicate plexiform capillary pattern. JAM is a benign condition best treated with complete conservative excision.(Hum Pathol, 23:639-646, 1992)
Contributed by Kevin J. Flynn, MD and Charles A. Richert, MD