Hoffa´s Fat Pad Chondroma

Clinical History

Male patient, 44 years old, with pain in the anterior right knee for one year. The patient refers swelling and restriction of range of motion. Physical examination revealed painful compression, increased volume of the infrapatellar region and restriction of flexion-extension.

Imaging Findings

Anteroposterior and lateral radiographs reveal a partially calcified mass within the Hoffa´s fat pad (Fig. 1).

T1-weighted SE MR images show a mass with mixed signal intensity within the infrapatellar fat pad (Figs. 2 and 3).

T2-weighted SE MR image reveals high signal intensity within the mass that represents oedema and chondroid matrix (Fig. 4).

T2* MR image shows high signal intensity with central areas of low signal intensity that represents calcifications (Fig. 5).

DP FATSAT SE MR images shows heterogeneous high signal intensity lesion (Figs. 6 and 7).

Discussion

Intracapsular chondroma, also known as extraskeletal chondroma, intracapsular osteochondroma and soft-tissue osteochondromais, is a rare lesion that results from extrasynovial metaplasia in the capsule or adjacent connective tissues. It is a benign cartilaginous soft tissue that may have foci of calcification, fibrosis and metaplastic ossification within it. It is considered by some as an end-stage form of Hoffa disease, given its similar location within the infrapatellar fat pad and similar pathologic feature of ossifying cartilaginous metaplasia.
It is characteristically located inferior to the patella and can produce bone erosion.

On radiographs it appears as a calcified mass within the infrapatellar fat pad.

Computed tomography usually shows a oval shaped soft-tissue mass with variable amount of ossification.

MR imaging: T2 and T2* weighted MR images demonstrates a heterogeneous mass with high signal intensity representing chondroid matrix or oedema and areas of low signal intensity representing calcification or ossification.

The most common differential diagnoses for this tumour are primary synovial chondromatosis and chondrosarcoma.

The treatment of choice is surgical excision.

Differential Diagnosis List

Final Diagnosis

Intracapsular chondroma

URL:	https://eurorad.org/case/8573
DOI:	10.1594/EURORAD/CASE.8573
ISSN:	1563-4086