Periosteal ganglion cyst masquerading as pes anserine bursitis

Periosteal ganglion cysts result from mucoid degeneration and cyst formation from periosteal tissue and are uncommon clinical entities. Long-standing periosteal ganglion cyst may present ith pain and pressure effect on underlying bone. Periosteal ganglion cysts at location near important bursa, in rare instances, may mimic bursitis and be misdiagnosed or treated inappropriately. Magnetic resonance imaging provides extensive details and delineation and is crucial for diagnosing these lesions. We report a case of 30-year-old female diagnosed and treated for pes anserine bursitis for months before radiological, and biopsy revealed a periosteal ganglion cyst spanning knee joint on medial aspect. Surgical excision as done to relieve the symptoms and there as no recurrence of the lesion noted in the follo-up.