synovial lipomatosis

Synovial lipomatosis is an uncommon tumor-like lesion of the synovium, usually affecting the suprapatellar pouch of the knee joints.

Synovial lipomatosis commonly affects adults.

The lesions predominantly occurred in older age groups and the median age was found to be 50 years, with 50% of the cases occurring after 50 years.

Synovial lipomatosis is a pesudotumorous lesion of the synovium, with distinct histomorphology, possibly resulting from inappropriate fat deposition and degenerative articular diseases of the joints.

Pathology

On histopathological examination, it closely resembles synovial lipoma and needs to be differentiated from it.

Intra-articular synovial lipoma is a much rarer lesion, usually affecting the knee joint, and clinically resulting in sudden pain and catching or locking of the knee.

Arthroscopy of the synovial lipoma shows a smooth, yellowish encapsulated mass, while histopathological examination shows an encapsulated mass, composed of mature adipocytes surrounded by the synovial membrane.

In contrast to this, synovial lipomatosis is characterized by a villous or frond-like architecture of the synovium, lined by mildly hyperplastic synovial lining cells and diffuse infiltration of the adipocytes of the subsynovial tissue.

Occasionally, a mild-to-moderate chronic inflammatory infiltrate may be present in synovial lipomatosis.

When synovial lipomatosis is examined macroscopically, the synovium has a characteristic papillary, yellow, fatty appearance.

Etiopathogenesis

The etiopathogenesis of this condition is still not understood. Causes that have been implicated include, trauma, inflammation, rheumatism, and developmental and neoplastic processes.

This change in the synovium possibly represents a protective and adaptive response to the longstanding injury of the articular cartilage.

The transformation in the synovial tissue can correspond to a metaplastic change in a chronically inflamed synovium.

A magnetic radio-imaging study may show a subchondral bone cyst or erosion in cases of synovial lipomatosis.

Another interesting finding in our study was a high body mass index in these patients. This draws our attention to the fact that synovial lipomatosis may be the result of excess fat deposition or fatty changes occurring due to obesity.

Direct injury to the articular cartilage may also lead to synovial lipomatosis, as noted in our case series in which one case was a sequel of Chikungunya and another occurred post-trauma.

Both these lesions would have led to destructive changes in the articular cartilage from post-inflammatory and traumatic processes.

Quite similar to osteoarthritis, the basic disease process was wear and tear of articular cartilage, resulting in its destruction. This signified a relationship of the articular cartilage with the synovium, thereby, causing changes in the synovium in the disease process affecting the articular cartilage.

Open References

 Pathology of synovial lipomatosis and its clinical significance. Rao S, Rajkumar A, Elizabeth MJ, Ganesan V, Kuruvilla S. J Lab Physicians. 2011 Jul;3(2):84-8. PMID: 22219560 [Free] http://www.jlponline.org/article.asp?issn=0974-2727;year=2011;volume=3;issue=2;spage=84;epage=88;aulast=Rao