Giant para-articular chondroma of the infra-patellar Hoffa's fat pad

Case contributed by Dalia Ibrahim
Diagnosis certain


Right knee swelling and limitation of movement.

Patient Data

Age: 50 years
Gender: Female

Large well-defined intra-articular infra-patellar osteocartilaginous lesion measuring 3.3x 3.2x 4.2cm along its max TS, AP & CC dimensions. The outer rim of the lesion shows a persistent dark signal on all pulse sequenced (osseous), white its center shows heterogeneous high signal on T2 & STIR WI (Cartilgnous). No post-contrast enhancement. The lesion causes anterior bowing of the patellar tendon yet it appears intact.

Mild synovial thickening is encasing the aforementioned lesion, eliciting isointense signal on T and high signal on T2 & STIR WI.

Mild knee osteoarthritis with mild joint effusion.


Large intra-articular infrapatellar loose body showing thick calcific margin.

Large intraarticular infra-patellar loose body.

Surgical excision of the large osteocartilaginous lesion revealed a large loose body.

Excision of the mild synovial thickening encasing the loose body which was seen on MRI revealed synovial capillary hemangioma.

Case Discussion

The case shows a large intra-articular loose body of the knee joint. It shows a characteristic signal on MRI with sclerotic margins eliciting dark signal on all pulse sequences and appears calcific on plain X-ray and CT scan, while its cartilaginous center shows high signal on T2 & STIR WI and appears lucent on X-Ray and CT study representing chondroid matrix.

Extraskeletal chondromas are benign tumors that appear in three variants:

  • synovial chondromatosis (common), giant solitary synovial chondroma is however a rare condition
  • para-articular chondroma (rare)
  • soft tissue chondroma (rare)

Para-articular chondromas/osteochondromas occur when the fibrous coat of the joint capsule or the para-articular connective tissue suffer from cartilaginous metaplasia.


  • It appears as a large rounded osteocartilaginous calcific lesion, ossification occurs peripherally, but ossification might also occur centrally sparing the peripheral cartilage resembling osteochondrma


  • solitary synovial chondromatosis
  • chondrosarcoma
  • paraosteal osteosarcoma
  • calcified lesions in Hoffa's fat pad, such as calcified old hematoma or bursitis
  • tumoral calcinosis or myositis ossificans

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