What It Is
A ganglion cyst is a sac of thick, jelly-like fluid that bulges out from a joint capsule or tendon sheath. The most common locations on the foot are the dorsal midfoot, the ankle, and over tendon sheaths.
What to Watch For
A firm or soft lump that may change size, sometimes painful when it presses on a nerve or rubs in a shoe. Diagnosis is largely clinical, supplemented by ultrasound or MRI when the lesion is atypical or when other masses must be excluded.
Treatment
Many ganglia can be observed if they are not painful. For symptomatic lesions, options include needle aspiration with corticosteroid injection (recurrence is common), and surgical excision - which has the lowest recurrence rate when the cyst stalk is removed back to its joint or tendon-sheath origin.