A 30-year-old woman presented with a history of chronic pain and an intermittent swelling of both her knees. A physical examination revealed bilateral swelling in the suprapatellar region. An MR examination of the left knee was performed.
The MR images demonstrated a synovial thickening in the suprapatellar bursa, with a signal intensity similar to that of fat on all pulse sequences, without joint effusion. After a gadolinium injection was administered, foci of synovial enhancement could be seen on the MRI.
Lipoma arborescens is a rare benign synovial disease characterized by villous lipomatous proliferation. The knee is the most commonly involved joint, with a predilection for the suprapatellar pouch. Bilateral involvement may occur. The clinical presentation includes a slow increase in swelling of the joint, usually over many years, associated with intermittent joint effusion. The erythrocyte sedimentation rate is found to be normal and the joint fluid aspirate is found to be sterile. Two patterns can be seen on MR images: a diffuse lipomatous thickening of the synovium, or the presence of synovial mass-like fat deposits. Joint effusion is often associated, while bone erosions are an infrequent occurrence. The differential diagnosis includes pigmented villonodular synovitis, which is characterized on an MR examination by the low signal intensity of hemosiderin deposition on T2-weighted images. Synovial osteochondromatosis and chronic rheumatoid arthritis are responsible for a low to intermediate signal on T1-weighted images. A synovial lipoma presents as a solitary round mass of fat without synovial changes. A synovial hemangioma contains foci of low signal intensity corresponding to the enlarged vessels of phleboliths. The treatment of choice for this condition is a synovectomy.
Lipoma arborescens.
Based on the MRI images of the patient’s knees, bilateral knee joints (with onset mainly in the left knee) show abnormal soft tissue thickening in the synovial regions, primarily in the suprapatellar pouch (suprapatellar bursa). This proliferative tissue demonstrates high signal on both T1- and T2-weighted images, similar to the signal of adipose tissue. There are signs of joint effusion, but no evident bone erosion or bony destruction. Overall, the synovium appears villous or arborized, indicating a “fatty” pattern.
Taking into account the patient’s chronic knee pain, recurrent joint swelling, and MRI findings, possible imaging differential diagnoses include:
Considering the patient’s age, clinical presentation, normal lab results (e.g., normal ESR, sterile joint fluid), and the MRI findings of “fatty” synovial thickening, the most likely diagnosis is:
Lipoma Arborescens.
Further confirmation usually does not require a biopsy. However, if clinical suspicion remains, arthroscopic evaluation and synovial biopsy can be performed to exclude other rare conditions.
During both post-surgical and conservative management phases, to reduce knee pain, prevent muscle atrophy, and facilitate early functional recovery, a step-by-step rehabilitation plan following the FITT-VP principle can be employed:
Throughout rehabilitation, avoid sudden increases in activity level and closely monitor for recurring joint swelling or exacerbated pain. If symptoms recur significantly, prompt review and adjustment of the rehabilitation plan is advised.
Disclaimer: This report is based on the analysis of existing images and clinical information for reference purposes only. It cannot replace in-person consultation or professional medical advice. If you experience any discomfort or special circumstances, please seek medical attention promptly.
Lipoma arborescens.
