Radiological Case: Bilateral Synchronous Involvement of Knee and Hip Joints With Primary Lipoma Arborescence in a Young Male

Ashwini Bakde Umredkar, MD; Amit Disawal, MD; Aarti Anand, MD; Prajwalit Gaur, MD; Jasdeep Kaur, MBBS


Appl Radiol. 2017;46(10):24-28. 

In This Article


Lipoma arborescence (LA) is a rare benign idiopathic intra articular lesion that involves the knee joint, particularly the supra patellar pouch.[1]

The Latin term "arborescence" (tree forming or tree-like) was given by Hoffa as the frond-like appearance of the synovium resembling a leaf in a tree.

The most common anatomical location is the knee joint, specifically the suprapatellar pouch, although cases have been described in many other synovial joints like the hip, shoulder, elbow, wrist and ankle.[2] Bilateral involvement is uncommon, but when bilateral joints are involved they usually occur at the same site.[3] In very rare cases, LA has been reported to affect multiple joints.[4]

The exact etiology of this condition is unknown and most of the cases arise de novo. Reports have described association with previous trauma, chronic rheumatoid arthritis, osteoarthritis, psoriasis or a baker's cyst.[5,6]

Before the era of MR imaging, it was difficult to confirm the diagnosis of lipoma arborescence radiologically. By the mid-1990s, only 13 cases had been reported in the literature. MR imaging proved to be the ideal modality for identifying the disease due to its excellent contrast resolution and sensitivity for fatty tissues.[7]

The commonest presentation of lipoma arborescence is the chronic painless swelling of the knee joint of several years duration. The swelling is usually non tender and soft in consistency. The symptoms of the patient are cyclical with intermittent exacerbations due to trapping of the lipomatous villi in the joint space.[8]

Radiologically, X-ray will demonstrate soft tissue swelling in the suprapatellar pouch with or without osteoarthritic changes. The soft-tissue swelling is predominantly due to the presence of effusion. Underlying fatty synovial proliferation giving lucencies may be obscured in most of the cases.[9] In our case, the patient had soft-tissue swelling in bilateral suprapatellar region.

High-resolution ultrasound findings include uniformly hyperechoic synovium based mass located in the suprapatellar bursa. Multiple finger-like globular and villous fronds can be seen extending from the base of the mass. Large anechoic effusions can be demonstrated in all patients. On color Doppler, no significant vascularity is seen. Dynamic compression of the villi demonstrates pliable nature of the villi.[10] Similar findings were noted in our case.

On MRI the characteristic appearances are multiple frond-like synovial proliferation of fat signal intensity and suppression of signal with fat selective presaturation. Other ancillary findings are associated joint effusion, potential chemical shift artifact and absence of magnetic susceptibility artifacts from hemosiderin.[7] Our case showed the characteristic finding of lipoma arborescence on MRI in both the suprapatellar pouches and in bilateral hip joints.

The major differential diagnoses of this condition are:

  1. Synovial osteochondromatosis: The radiographic findings of synovial osteochondromatosis consist of multiple intraarticular calcified nodules, characteristically uniform in size. The MR imaging appearance is variable and depends on the relative proportion of synovial proliferation and calcified nodule formation. Non-mineralized lesions tend to form an intraarticular mass that is isointense to muscle on T1-weighted images and hyperintense on T2-weighted images. When the cartilaginous nodules contain calcification, small areas of low signal intensity are observed with all pulse sequences.[11]

  2. Pigmented villonodular synovitis: On MR images, the mass-like proliferative synovium has a lobulated margin. The lesions tend to bleed, causing hemosiderin deposition and characteristic low signal intensity with all pulse sequences.[12]

  3. Synovial hemangioma: MR imaging findings of synovial haemangioma are frequently pathognomonic, consisting of a lobulated intraarticular mass. The mass usually has intermediate signal intensity on T1-weighted images, and it is markedly hyperintense on T2-weighted images, which reflects pooling of blood within vascular spaces.[13]

  4. Synovial lipoma: Intra-articular synovial lipoma appears as a small, single, polyp-like mass, round to oval in shape, with a short stalk arising from the fat pad area of the suprapatellar pouch, whereas lipoma arborescence appears as a frond-like mass.[8]