A Giant Ganglion Cyst Arising from Lateral Hoffa's Fat Pad of the Knee.

INTRODUCTION: The ganglion cysts are benign fluid-filled sacs, which often arise from a tendon sheath or a joint capsule. Their origin from the fat pad of the knee is rare. Several studies have described intra-articular ganglion cysts in detail; however, extra-articular soft-tissue ganglion cysts have been reported sparingly. We report a rare case of giant ganglion cyst arising from lateral Hoffa's fat pad (HFP). CASE REPORT: A 59-year-old male patient presented with a 3-year history of swelling of the left knee, with occasional pain. There was no history of trauma or any constitutional symptoms. There was an apparent swelling (10 cm ×5 cm in size) around the anterolateral aspect of the knee joint. A magnetic resonance imaging (MRI) scan revealed a multilobular, complex cystic lesion of the lateral HFP. Surgical excision of the cyst was done, and histopathological examination confirmed the diagnosis of the ganglion cyst. CONCLUSION: Cysts and cystic-appearing lesions around the knee are not uncommon, but a ganglion cyst arising from HFP is rare. The presence of multipotent cells in the HFP may be responsible for producing a variety of cyst and cyst-like tumors around the anterior aspect of the knee joint. An MRI is the best imaging modality for the diagnosis of these cysts and cysts-like lesions around the knee. We recommend that the smaller intra-articular lesions can be resected arthroscopically, but larger lesions, with extraarticular extension, are best treated by open resection to avoid incomplete excision and recurrence.