Lipoma arborescens (tree like, diffuse articular lipomatosis) is a rare, benign intra-articular lesion of unknown aetiology. It is a very rare primary benign tumour of the synovium, and forms part of the differential diagnosis for a slowly progressive chronically swollen knee.
About 50 cases of Lipoma arborescens have previously been reported, usually involving one knee, with occasional reports of involvement of other joints including the hip, shoulder, wrist and elbow. Lipoma arborescens is usually mono-articular.
Drs A.P. Davies and N. Blewitt, from the Avon Orthopaedic Centre, Southmead Hospital, United Kingdom have recently presented a very rare case of bilateral involvement of the knee and discuss the symptoms, diagnosis and treatment of this condition.
The authors, writing in the October issue of The Knee, have presented the case history of a fit and well 32-year-old man, who first presented to his general practitioner in 1988 with painless progressive swelling of both knees, which later on changed to slowly progressing pain and stiffness. The authors also review that patients with lipoma arborescens usually present with a long-standing, slowly progressive swelling of the affected joint. There may be a restricted range of movement, effusion or pain. Clinically there is a soft, boggy swelling in the suprapatellar pouch. Some patients have no other musculo-skeletal disorder but associated conditions have been reported to include osteoarthritis, local trauma to the joint and diabetes mellitus. Patients have been reported between the ages of 9 and 68 years and lipoma arborescens appears to be equally common in men and women.
Macroscopically lipoma arborescens is a bulky mass of tissue with a frond-like appearance of numerous broad based villi composed of fatty yellow tissue. Histologically, the villi of lipoma arborescens are composed of mature adipose tissue, which displaces most of the connective tissue around the knee to a layer of synovial cells. Enlarged or congested hyperaemic capillaries may be present. High power histological sections show large adipocytes and few other features. The overlying synovial cells may appear enlarged and reactive with abundant eosinophilic cytoplasm.
Medical management with intra-articular injection of radio-active compounds such as Yttrium 90 or steroids may lead to resolution of symptoms in the short to medium term. In the case described above, Yttrium treatment gave relief of symptoms for 2 years before surgical treatment was required. The surgical treatment of lipoma arborescens is complete excision. Formal open synovectomy is held to be curative with only a single case of recurrence having been reported. Open synovectomy does however carry some short-term morbidity. Arthroscopic synovectomy has been described with no recurrence at short durations of follow up.