A rare case of Hoffa's fat pad herniation in a young patient: dynamic ultrasound and MRI diagnosis.

Hoffa's fat pad (HFP) is part of the knee structure interposed between the joint capsule and the synovium. Recent studies have classified infrapatellar fat pad (IFP) disorders on a pathogenesis-based classification: traumatic disorders, post-traumatic disorders, lesions secondary to adjacent disorders. Masses or pseudo-masses may also be found within the IFP, however these alterations are much less frequent. Diagnostic imaging plays an important role in the diagnosis of masses and pseudo-masses of IFP and the first choice exam is a dynamic ultrasound study. We presented a rare case of Hoffa's fat pad herniation through the joint capsule, in a young child without history of knee injuries that has never been described before in the literature.