Lipoma arborescens with severe osteoarthritis and internal derangement of the knee joint

Case contributed by Mohammad A. ElBeialy
Diagnosis certain


Chronic eft knee pain and swelling.

Patient Data

Age: 45 years.
Gender: Female

Degenerative changes of the articular cartilage with thinning and denudation as well as subchondral degenerative change; most evident at the medial tibio-femoral articulation with lateral femoral condyle subchondral 3.5 X 2.7 cm cystic lesion associated with extensive perilesional osseous edema as well as a similar yet much smaller distal femoral intercondylar subarticular cystic lesion. Osteoarthritic changes with subtle marginal osteophytic lipping of the tibio-femoral and patella-femoral articulations.

Degenerative tear of the posterior horn medial meniscus (PHMM) with an intra-mensical branching signal of increased signal intensity seen reaching the inferior articular surface. 

No definite lateral meniscal tear.

Mucoid degeneration of the ACL which appears thickened with increased signal intensity alternating with its normal hypointense fibers. 

Intact fibers' continuity with normal MR signal of the posterior cruciate and collateral ligaments as well as the quadriceps tendon and patellar ligament.

Moderate knee joint effusion with synovial thickening and frond-like synovial projections with high T1 signal and intermediate to high T2 signal as well as signal suppression in the FAT-suppression sequences.

A small pes anserinus bursitis is noted. No Baker's cyst. 

CT confirms the synovial frond-like fat-density mass lesions; consistent with lipoma arborescens with 2ry severe osteoarthritis of the knee joint and moderate joint effusion.  

Case Discussion

Moderate joint knee joint effusion with synovial thickening and frond-like synovial projections of fat-density and signal intensity; impressive of lipoma arborescens with degenerative joint disease and severe osteoarthritic changes of the knee joint as well as lateral femoral condyle subchondral cystic lesion; likely subchondral Geode rather than intraosseous ganglion or chondroblastoma with extensive perilesional osseous edema, degenerative tear of the posterior horn medial meniscus (PHMM), early mucoid degeneration of the ACL & a small pes anserinus bursitis.

Lipoma arborescens is idiopathic, however unusual nonspecific reactive response to chronic synovial irritation, either mechanical or inflammatory insults is suggested. It is considered as a lipoma-like benign synovial villous proliferation with replacement of the subsynovial connective tissue by mature fat cells.

The radiological signs are frond-like fat-density or signal intensity synovial lesions (ranging from small frond-like proliferations to large infiltrating fronds of hyperplastic synovium and eventually large rounded or globular fatty mass lesions) usually located within the suprapatellar bursa.

The clinical presentation is usually painless swelling of the knee, with pain later on from accelerated osteoarthritis and internal derangement of the knee. 

Treatment is synovectomy (before osteoarthritis and internal derangement prevail).

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