A 14-year-old woman was referred to rheumatology for polyarthralgias (lumbar, right ankle and bilateral knee pain). After the initial clinical and laboratory studies, no definite diagnosis was achieved.
The most affected joint was the left knee, with progressive swelling and pain during the past 3 months.
The initial plain film demonstrated opacification of the suprapatellar fat pad suggesting joint effusion. There were no other relevant radiographic abnormalities.
MRI showed moderate joint effusion and frond-like synovial proliferation that follows fat signal intensity in all pulse sequences. No other abnormalities were found.
Lipoma arborescens is an idiopathic joint lesion, characterised by villous lipomatous proliferation replacing the subsynovial tissue [1]. Generally it is monoarticular and most commonly occurs in the knee, but other joints and bursas can be affected.
This condition is thought to represent a non-specific synovial reaction to trauma and inflammation. The strong association with degenerative joint disease, chronic rheumatoid arthritis and seronegative spondyloarthropaties supports this hypothesis [2].
However, in some patients (generally young) it can be lacking other joint findings. So, some authors propose that in these cases these lesions should be categorised rather as primary lipoma arborescens, as opposed to the secondary / reactive form [3].
It has a nonspecific clinical presentation. Although it can be asymptomatic, it is often associated with intermittent pain, swelling and movement range restriction.
The main differential diagnoses include pigmented villonodular synovitis, synovial chondromatosis and synovial haemangiomatosis, but the differentiation by MRI is generally easy [4].
Radiographic findings are nonspecific. It may be noted a soft-tissue density in the suprapatellar pouch. Ultrasound findings include proliferation of the synovial membrane with frond-like masses and effusion.
MRI appearance is diagnostic. Generally there is a frond-like synovial mass that has the same signal intensity of fat in all sequences. Usually, there is also joint effusion and lack of magnetic susceptibility artefacts in gradient-echo sequences.
There have been reports of lipoma arborescens appearing as a more focal pseudo-mass [2].
Generally, treatment consists of curative open or arthroscopic synovectomy. Some authors consider medical management options like intra-articular injection of radio-active compounds such as Yttrium 90 or steroids [5].
Lipoma arborescens of the knee
Based on the provided X-ray and MRI images, there is a notable proliferative soft tissue shadow in the left knee joint cavity, showing multiple lobulated or villous projections. MRI demonstrates that the lesion appears with high signal intensity similar to fat on different sequences (T1- and T2-weighted images), and no significant susceptibility artifact is observed. A certain amount of joint effusion can be seen, with no obvious destructive changes to the bone. Overall, these findings suggest abnormal synovial thickening predominantly involving fatty proliferation, indicating a synovial fatty proliferative lesion.
Considering the patient’s young age of 14, gradual swelling of the left knee, the characteristic “villous” fatty proliferation on imaging, and the absence of clear joint degeneration or other joint pathology, the most likely diagnosis is Primary Lipoma arborescens.
Treatment Strategy:
1. Surgical Treatment: For lipoma arborescens with significant symptoms or functional impairment, arthroscopic or open synovectomy (synovial resection) is commonly performed and generally achieves good symptom relief and outcome.
2. Pharmacological or Adjunctive Therapy: If recurrent swelling occurs after arthroscopic treatment, intra-articular steroid injection or radioisotopes (e.g., Yttrium 90) may be considered to reduce synovial proliferation. This is typically supplementary and should be done under close specialist supervision.
3. Other Conservative Management: If the lesion is small and symptoms do not warrant surgery, non-steroidal anti-inflammatory drugs, joint functional exercises, and regular imaging follow-up can be adopted to observe disease progression.
Rehabilitation / Exercise Prescription (FITT-VP Principle):
1. Type: Start with low-impact exercises conducive to improving joint range of motion and stability (e.g., swimming, low-resistance cycling), to reduce joint stress and promote circulation.
2. Frequency: 3–5 times a week, gradually increasing based on the patient’s recovery of joint function.
3. Intensity: Initially low intensity. According to the Rate of Perceived Exertion (RPE) scale, keep it at a light to moderate level (RPE 2–3), and increase gradually as symptoms improve and joint stability enhances.
4. Time: Begin with 20–30 minutes per session, then gradually extend to approximately 45 minutes based on tolerance and pain level, or split into multiple sessions.
5. Progression: After initial pain and swelling are controlled, gradually introduce light strength training (e.g., resistance band exercises, wall sits) to strengthen the quadriceps, under professional supervision.
6. Special Considerations: If there is marked increase in swelling or acute exacerbation of pain, stop or modify the exercise to prevent further injury. Braces or additional protective measures can be used as needed.
Disclaimer: This report is for reference only and does not replace an in-person consultation or professional medical advice. Should you have any questions or changes in your condition, please consult a specialist or visit a hospital.
Lipoma arborescens of the knee
