Soft tissue chondroma of the Hoffa fat pad

Last revised by Mostafa Elfeky on 5 Dec 2022

Soft tissue chondroma of the Hoffa (infrapatellar) fat pad is a rare form of chondroma. It is considered by some to be the end-stage of Hoffa disease of the infrapatellar fat pad

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
    • fibrocartilage
    • 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

Features include

  • T1

    • 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

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