Infrapatellar Fat Pad Mass

Differential considerations for a mass in the infrapatellar fat pad:

• Hoffa disease: Painful condition caused by acute or repetitive trauma producing hemorrhage and necrosis of the infrapatellar fat. Acute phase demonstrates edema and outward bowing of the patellar tendon. Chronic phase is characterized by fibrin and hemosiderin deposition, with ill-defined margins.
• Focal nodular synovitis: Benign proliferative disorder arising from a small area of the synovium. Most frequently in the tendon sheaths of the small joints of the fingers and toes. Well-defined ovoid or polylobulated soft-tissue mass. Iso- or hyperintense relative to skeletal muscle on T1-weighted images. Variable signal intensity on T2-weighted images. May have regions of high hemosiderin concentration.
• Chondroma: Cartilage signal pattern
• Osteochondroma: Bone marrow signal pattern.
• Gouty tophus:

References

Huang GS, Lee CH, Chan WP, Chen CY, Yu JS, Resnick D. Localized nodular synovitis of the knee: MR imaging appearance and clinical correlates in 21 patients. AJR Am J Roentgenol. 2003 Aug;181(2):539-43.