Thanks for posting your query.
A ganglion cyst
, also known as a Bible cyst, is a swelling that often appears on or around joints and tendons in the hand or foot. These occur as "an out-pouching or distention of a weakened portion of a joint capsule or tendon sheath.
You can watch for a period if it not bother him.If it causes pain and causes compression features or for cosmetic purposes, it can be removed surgically.
Wishing you good health
Dr Saurabh Gupta