Pain of the left knee.
The patient complained of pain in his left knee of a few years' duration. Plain films and MR imaging of the knee were performed.
Plain films showed non-specific degenerative changes, with no evidence of effusion. MR imaging, in addition to a posterior horn tear of the medial meniscus, revealed a frondlike mass in the suprapatellar pouch and a small effusion.
A diagnosis of lipoma arborescens of the knee was made.
Lipoma arborescens (or the more correct term, villous lipomatosis proliferation of the synovial membrane, as there is no neoplasm) is a rare intra-articular lesion consisting of villous lipomatous proliferation of the synovium that tends to occur in the knee joint, particularly in the suprapatellar region. It is monoarticular in distribution and is most commonly seen at the knee joint. The condition is very rare in other joints (glenohumeral joint, sub deltoid bursa, hip and elbow). It is virtually unknown outside the joint capsule. The underlying bone is usually normal.
The precise aetiology is unknown, but it is most likely a non-specific synovial reaction to trauma and inflammation. It can be associated with degenerative joint disease (as in this case) and chronic rheumatoid arthritis.
True lipoma arborescens is a discrete histological entity and is characterised by the diffuse sub-synovial deposition of fat and a villous appearance. Synovial lipoma is a solitary localised mass of adipose tissue with a round or oval contour.
The typical clinical presentation of lipoma arborescens is a slowly progressive and painless joint swelling. Mechanical symptoms of locking may occur with joint tenderness and crepitus.
On plain radiographs it appears as soft tissue swelling which may or may not be radiolucent. Arthrography reveals multiple filling defects. Ultrasound shows a hyperechoic, frondlike mass in the suprapatellar bursa with a large associated effusion. The frondlike mass shows bending and waving in real time.
MR findings include a large frondlike mass arising from the synovium with a signal intensity similar to that of fat on all sequences, and an associated effusion. There is no evidence of haemosiderin deposition. It may be associated with a chemical shift effect and secondary involvement of adjacent fat pads.
The differential diagnosis includes synovial disorders such as synovial lipoma (a solitary localised mass of adipose tissue with a round contour without synovial changes), synovial osteochondromatosis (intermediate signal intensity within the synovium on T1-weighted images and variable on T2-weighted images due to the cartilaginous nature), pigmented villonodular synovitis (which shows low signal intensity in the synovium with haemosiderin deposition), synovial haemangiomatosis (intermediate signal on T1- and T2-weighted images), xanthoma, plexiform neuroma and vascular malformations.
The recommended treatment is synovectomy.
Lipoma arborescens of the knee
The patient is a 45-year-old male, presenting with left knee pain. MRI (coronal and sagittal views) shows:
Overall imaging findings suggest synovial proliferation primarily composed of fatty tissue (“fat signal”) coexisting with joint effusion.
Based on the patient’s clinical symptoms and the aforementioned imaging findings, the following differential diagnoses are considered:
Considering the patient’s age, symptoms (knee pain with possible intermittent joint locking or effusion), and imaging findings (multi-lobulated, fat-signal proliferation paired with joint effusion, without significant hemosiderin deposition or cartilaginous/osseous nodules), the most likely diagnosis is:
Lipoma Arborescens.
If there is any doubt about the diagnosis, arthroscopic evaluation or biopsy may be performed for confirmation.
As this condition primarily involves synovial proliferation leading to joint pain and effusion, postoperative or conservative management should include appropriate exercises that safely and gradually restore joint functionality.
Throughout rehabilitation, individual factors (such as bone health, cardiopulmonary fitness, and body weight) should be taken into account, following a gradual progression methodology aligned with the FITT-VP principle (Frequency, Intensity, Time, Type, Volume/Progression, and Personalization).
Disclaimer: This report is a reference-based analysis derived from the available imaging and medical history. It does not replace in-person consultation or professional medical advice. If you have any questions or if your symptoms worsen, please seek medical attention promptly.
Lipoma arborescens of the knee
