Quadriceps fat pad edema: significance on magnetic resonance images of the knee.

OBJECTIVE

While clinically reading magnetic resonance (MR) images of the knees we have occasionally noted edema within the suprapatellar fat pad, with mass effect both on the suprapatellar joint recess posteriorly, and on the quadriceps tendon anteriorly. This MR appearance is analogous to Hoffa's disease described in the infrapatellar fat pad. We sought to evaluate the frequency and pattern of this finding and to provide clinical and histological correlation.

PATIENTS: The suprapatellar (quadriceps) fat pad was evaluated in 770 consecutive MR examinations (on 1.5 T and 0.3 T) in 736 patients (353 females and 383 males, age range 5-86 years, mean 44.3 years).

DESIGN

The MR images were retrospectively evaluated by two observers in consensus for the presence of quadriceps fat pad edema with mass effect. In 46 patients who had intravenous administration of gadolinium, the presence of enhancement was also evaluated. Clinical correlation was performed in abnormal cases; in one patient, 1-year follow-up MRI was evaluated and in one patient a percutaneous biopsy as well as 2-year clinical follow-up was performed.

RESULTS

Thirty-two (4.2%) knees in 29 patients showed quadriceps fat pad edema and mass effect. In five of these patients imaging of the contralateral knee was also performed and four of these showed symmetric edema. Another five cases had gadolinium-enhanced images with prominent enhancement. Most patients had clinical symptoms of meniscal tears (n=16, 55%) or anterior knee pain (n=8, 27.6%). The remainder had nonspecific pain (n=4, 13.8%) or suspected avascular necrosis (n=1, 3.4%). In the case with 1-year follow-up MRI, improvement was seen. Biopsy in another patient revealed vasculitis with obliteration of the small vessels. Resection of the fat pad in this patient led to complete resolution of the symptoms.

CONCLUSION

Suprapatellar fat pad edema may be analogous to Hoffa's disease, is rare, and may be a cause of anterior knee pain. However, this finding is not infrequent and its precise association with symptoms remains unclear.