The condition usually presents in adults with chronic anterior knee pain as well as a hard swelling inferior to the patella.
The pathogenesis of this condition is unclear but several theories exist. It may occur as a result of metaplasia from mesenchymal cells due to acute or repetitive trauma related to hyperextension of the knee and subsequent inflammation and hemorrhage 4.
- lobulated mass of hyaline cartilage
- endochondral ossification in the central areas
- variable areas of:
- myxoid tissue
- fibroadipose tissue
The variety of tissues present accounts for its heterogeneous and variable MRI appearance.
Arc-like calcifications and ossified areas in the infrapatellar fat pad, corresponding to variable endochondral ossification predominant in the central areas of the lobulated mass.
- lobular mass with acoustic shadowing
- nodular partially calcified cartilaginous mass
- mass in the Hoffa fat pad
- generally low signal
- isointense to muscle
- some dark areas signifying calcification
- T2: high signal in the cartilaginous components
- PD: as above with T1, plus high intensity signal areas corresponding to medullary bone
- GRE: prominent signal voids within a nodular mass
Possible considerations include
- it is important not to rely solely on MRI or US imaging features alone as the appearances can be variable
- contrast enhancement can occur and does not necessarily imply malignancy
- it is important to correlate the MRI findings with plain radiographs or CT
- 1. Albergo JI, Gaston CL, Davies M, Abudu AT, Carter SR, Jeys LM, et al. Hoffa's fat pad tumours: what do we know about them?. Int Orthop. 2013 Nov; 37(11): 2225–2229.
- 2. Ingabire MI, Deprez FC, Bodart A, Puttemans T. Soft tissue chondroma of Hoffa's fat pad. (2012) JBR-BTR : organe de la Societe royale belge de radiologie (SRBR) = orgaan van de Koninklijke Belgische Vereniging voor Radiologie (KBVR). 95 (1): 15-7. Pubmed
- 3. Krebs VE, Parker RD. Arthroscopic resection of an extrasynovial ossifying chondroma of the infrapatellar fat pad: end-stage Hoffa's disease? Arthroscopy. 1994 Jun;10(3):301-4. Pubmed
- 4. Turhan E, Doral MN, Atay AO, Demirel M. A giant extrasynovial osteochondroma in the infrapatellar fat pad: end stage Hoffa's disease. Arch Orthop Trauma Surg. 2008 May;128(5):515-9. Epub 2007 Jul 24. Pubmed