Hoffa's fat pad ganglion cyst of the knee: a case report of a rare cause of knee pain and swelling.

Abstract

Hoffa's fat pad (HFP), also known as infrapatellar fat pad, is one of the three fat pads in the knee. Ganglion cyst (GC) rarely arises from HFP which presents knee pain and swelling. A 43-year-old female presented with left knee pain for 1 year and swelling in her left knee for 6 months. Clinical examination revealed a palpable swelling of size around 3cm×2cm over the anteromedial aspect of the left knee. The size of the swelling increased on extension and decreased on flexion of the knee. A musculoskeletal ultrasound of the left knee revealed a lobulated anechoic lesion of size ∼2.3cm×2cm in HFP. Open excision of cystic mass through medial parapatellar approach was done, and histopathological examination showed findings consistent with GC. At 6 months follow-up, there was no residual swelling and no recurrence. She was symptom-free on her recent evaluation after 1 year of operation. GCs arising from HFP are much rarer among the cysts around the knee. Diagnosis is primarily done by magnetic resonance imaging. However, the use of ultrasonography has grown in the diagnosis of the GC. Among different modalities of treatment, open excision is the most recommended to prevent recurrence and incomplete resection. This case illustrates the importance of ultrasonography in the early diagnosis of HFP GC and reserving more costly and time-consuming imaging modality magnetic resonance imaging for localizing the extent of the cyst. We recommend an open resection to avoid recurrence and incomplete resection of the cyst.