Differential diagnosis of tumours and tumour-like lesions of the infrapatellar (Hoffa?s) fat pad: pictorial review with an emphasis on MR imaging

Abstract

A variety of intrinsic and extrinsic tumours and tumour-like conditions may affect the infrapatellar (Hoffa's) fat pad (IFP). MR imaging is the technique of choice in evaluating these conditions, but correlation with radiographs is important to identify those lesions producing mineralization. This pictorial review illustrates the spectrum of mass-like lesions that can affect the IFP, emphasizing the radiographic and MR findings that suggest a specific diagnosis.

Soft tissue chondroma of Hoffa's fat pad

“…Para-articular chondroma, also known as extraskeletal chondroma or soft tissue chondroma, may be a result of metaplasia from mesenchymal cells (2). Some authors consider it as the end stage of Hoffa's disease (5) resulting from acute or repetitive trauma related to hyperextension, rotational sprains and also genu recurvatum.…”

Deformation analysis of Hoffa's fat pad from CT images of knee flexion and extension

“…4 Helpert et al presented a pictorial review of tumours and tumour-like lesions of the infrapatellar fat pad of Hoffa with an emphasis on differential diagnosis from MR imaging. 5 Another recent review was also published recently by Saddik et al on Hoffa's fat pad in MRI. 6 In this paper we investigate the 3D shape deformations of Hoffa's fat pad (Figure 1), between knee flexion and extension as a possible indication of a bio-mechanical behavior (cushioning) in addition to the classical energy storage function.…”

Arthroscopic Resection of Fat Pad Lesions and Infrapatellar Contractures

“…The MRI study is also useful in showing causes of knee pain from other sources in the fat pad, such as ganglion cysts, pigmented villonodular synovitis, calcified lesions, and other lesions within the IFP. 6,7 Direct injection of lidocaine into the IFP is another diagnostic tool that should be considered. The fat pad is a known source of substance P, which affects pain mediation by increasing sensitivity to nociceptive signals and promotes inflammation by vasodilation, extravasation of plasma proteins, and adherence of leukocytes.…”