Presentation
Right knee swelling and limitation of movement.
Patient Data
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.
Radiologically:
- It appears as a large rounded osteocartilaginous calcific lesion, ossification occurs peripherally, but ossification might also occur centrally sparing the peripheral cartilage resembling osteochondrma
DDx:
- 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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