7 December 2006 – Case of the Week #66
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We thank Dr. Ronald M. Angeles, University of Pittsburgh, Pennsylvania (USA), for contributing this case. We invite you to contribute a Case of the Week by sending an email to NPernick@PathologyOutlines.com with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a short clinical history, your diagnosis and any other images (gross, immunostains, EM, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you a check for $35 (US) for your time after we send out the case. Please only send cases with a definitive diagnosis.
Case of the Week #66
A 71 year old man complained of a slowly growing mass in the left popliteal fossa. CT scans and MRI studies showed a well-circumscribed mass without invasion of the surrounding neurovascular bundle, bone or soft tissues.
The mass consists mostly of confluent and occasionally discrete lobules of moderately cellular hyaline cartilage. There is focal endochondral ossification. Cellular atypia is mild. No mitotic figures or necrosis are identified.
What is your diagnosis?
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Synovial chondromatosis of the popliteal fossa
Synovial chondromatosis is also called synovial chondrometaplasia or synovial osteochondromatosis. It may be primary or secondary to other joint disease. It typically affects men, with a mean age of 41 years, but a range of 17 to 64 years.
Primary cases are uncommon, and often aggressive. They are typically monoarticular, and affect the knee, hip, elbow and their communicating bursae, with occasional infiltration into adjacent soft tissue (Pathologica 2001;93:132). Radiographs usually show calcific densities within a joint, although they may also be negative.
Secondary cases occur due to degenerative joint disease, neuropathic arthropathy or osteochondritis dissecans (Hum Path 1979;10:439).
On gross exam, numerous round osteocartilaginous nodules cover a thickened synovial surface or float freely within the joint space. Microscopically, there are cartilaginous cells with variable atypia or binucleated forms within synovium.
The differential diagnosis includes benign chondroma of soft tissue and low grade chondrosarcoma. The extra-articular form of synovial chondromatosis, called tenosynovial chondromatosis, resembles chondroma of soft tissue, in that both occur in the soft tissue of the hands and feet, and both lack a connection to bone (AJSP 2003;27:1260). However, chondromas lack a synovial or tenosynovial layer or subsynovial connective tissue that is present in chondromatosis. Chondrosarcomas typically do not arise from within a joint. They lack a characteristic clustering pattern, and have marked myxoid change and spindling of nuclei.
Treatment of synovial chondromatosis consists of excision, but it frequently recurs. These tumors become malignant in about 5% of cases (Hum Path 1998;29:683)
Nat Pernick, M.D., President
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