Indian Journal of Pathology and Microbiology

: 2016  |  Volume : 59  |  Issue : 2  |  Page : 235--237

Synovial osteolipoma

Radha Sistla1, Josyula Venkata Satya2, Tameem Afroz1,  
1 Department of Anatomical Pathology, Cytology, Global Hospitals, Hyderabad, Telangana, India
2 Department of Orthopaedics and Sports Medicine, Cytology, Global Hospitals, Hyderabad, Telangana, India

Correspondence Address:
Radha Sistla
Sistla, Plot No. 20, Road No. 1, Alakapuri, L.B Nagar, Hyderabad - 500 035, Telangana


Intraarticular synovial osteolipoma is an extremely rare tumor. Only two cases have been reported earlier to the best of our knowledge. It is a rare histological variant of lipoma, which contains mature lamellar bone. The largest tumor reported so far in the joint is 3 cm × 4 cm. Knee is a most common site. We report a large osteolipoma measuring 12 cm × 10 cm in the knee.

How to cite this article:
Sistla R, Satya JV, Afroz T. Synovial osteolipoma.Indian J Pathol Microbiol 2016;59:235-237

How to cite this URL:
Sistla R, Satya JV, Afroz T. Synovial osteolipoma. Indian J Pathol Microbiol [serial online] 2016 [cited 2023 Jan 27 ];59:235-237
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Tumors of the synovium are rare. Lipomas are the largest group of mesenchymal tumors of soft tissue. Tumors composed of adipose tissue that occur in synovium are very rare. Common adipocyte lesions in the joint are lipoma and lipoma arborescens. Various types of tissues like smooth muscle, fibrous tissue, vascular elements, and osteochondral tissues occur in soft tissue lipomas. Osseous metaplasia in synovial lipomas is very rare. Osteo-lipomas are described in various in extra articular locations. Rochelle et al. first described an intraarticular lipoma with osseous metaplasia, since then very few cases of synovial osteo-lipoma were described. The case under discussion is rare (1) in view of its incidence and (2) in view of its massive size.

 Case Report

A 60-year-old lady presented with pain and swelling of right knee joint of 8 years duration. There was restriction of mobility of the joint for the last 6 years. Swelling was insidious in onset with progressive increase in size. There was no relief of pain with analgesics. She also complained of locking and instability of the joint. She was unable to squat on the ground. Swelling was localized to lateral side of patella. There is no history of any constitutional symptoms. She is a not known diabetic; she was a hypertensive on irregular treatment. On examination, mass was seen on lateral side of patella, measured 12 cm × 10 cm. It was freely movable side to side but was not moving longitudinally. There was a fixed flexion deformity of 110°. Limp was present on walking. Skin over the swelling was stretched. There were no signs of inflammation.

Her routine hematological and biochemical parameters were within normal limits. Her viral screening was negative.

Plain radiographs showed osteoarthritis grade 4, both knees with varus deformity. AP view showed a lobulated expansile lesion lateral to patella, which is calcified. Magnetic resonance imaging showed a lobulated mass lesion [Figure 1] adjacent to bone but not attached to the patella. Mass had thick hypointense margins and was septae with lobulation. Effusion was present with degenerative changes in menisci and ligaments.{Figure 1}

Open biopsy was done. Effusion was aspirated before opening the joint. Fluid was pale yellow with cartilage debris. Hard mass was found in the suprapatellar pouch covered by synovium. Mass measured 12 cm × 10 cm in long axis. Surface was smooth with hard bony feeling at the periphery and soft to cystic in the center. Mass could be easily excised intact and was sent for histological examination.

Grossly mass had a lobulated appearance, surface was smooth measuring 12 cm × 10 cm. Cut section revealed a yellow greasy mass with hard rim and septae of variable thickness [Figure 2]. Histological sections revealed a well-encapsulated lesion composed of lobules of mature adipocytes, separated by fibrous septae. Extensive areas of osseous metaplasia within the adipocytes were seen. Bony lamellae appear mature. No atypical features were seen in the adipocytes or the osseous elements [Figure 3].{Figure 2}{Figure 3}


Tumors of synovium are rare, the most common lipomatous lesion in the synovium is lipoma arborescens. True intraarticular synovial lipoma is a rare neoplasm, whereas lipomas of soft tissues are very common. Various mesenchymal elements like smooth muscle, fibrous tissue, chondral and osseous tissues occur in lipomas.[1] Approximately, fourteen histological types of adipose tissue tumors are described. Lipomas with distinct osseous metaplasia are very rare and occurs in <1% of lipomas.[2] These lesions were first described in 1959. They are even rarer in the intraarticular location. Only two cases have been described in literature. Several names were used to describe ossification in lipomas like lipomas with secondary calcification, ossified lipoma, ossifying lipoma, and osteolipoma. Lipomas containing mature osseous elements are called osteolipomas. The term ossifying lipoma, osseous lipoma, and lipoma with osseous metaplasia are used interchangeably with osteolipoma.[3] Some authors call lipomas composed primarily of fat as ossifying lipomas and those in which fat is not the primary component as osteolipomas.[4] Lesions in the joint which have ossification are synovial chondromatosis, osteochondral fractures and synovial chondrosarcoma. Lesions which contain fat are lipomas and lipoma arborescens. The coexistence of osseous and fatty tissue in the synovium is rare. Intraarticular lesions usually present with mechanical problems and swelling. Presence of bone does not alter the prognosis of these lesions. Very few lesions are described in the joint, the pathology and pathogenesis of these lesions is probably similar to that described in soft tissues. They are reported in various locations. Like lipomas, these lesions also have a wide distribution, they occur in soft tissues adjacent to bone or periosteum, including the extremities, oral mucosa, soft tissues of neck, intracranial region including tuber cinerium, hypothalamus, suprasellar cistern, and interhemispheric area.[5]

Jaffe described the origin of these lesions from sub synovial fat near the patellar ligament. It can also arise from fat pad anterior to surface of femur, from synovium near anterior horn of medial meniscus or from posterior wall of supra patellar bursa. In the present case, the lesion was located close to the fat pad near patellar ligament.

Pathogenesis of osteolipoma is unknown. Two theories are proposed. One is that these tumors arise from multipotent mesenchymal cells and the second hypothesis is that secondary ossification occurs because of repeated trauma or ischemia.[6] Adipocytes can promote osteoblastic proliferation through differentiation factors secreted by fat cells. Prognosis in osteolipomas is similar to lipomas. Treatment is surgical excision. Recurrences are not reported.


Lipomas with mature bone are called osteolipomas. Their occurrence in the joint is very rare. The purpose of presenting this case is its rarity and size of the lesion. Lesions with heterologous elements can give rise to suspicion of atypical lipomatous tumors. We describe a large intraarticular lipoma with extensive osseous metaplasia. Patient is on regular follow-up and is symptom free during the last follow-up.

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Conflicts of interest

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