These are cystic lumps that arise from the end joint of fingers and thumb. It starts as a small lump and gradually increases in size causing the skin to become very thin and translucent.
Sometimes it ruptures discharging clear slimy fluid. After discharge it usually subsides only to recur again.
The cause of these cysts is an underlying arthritic joint which forms excess fluid which pushes out forming these cysts. It is for this reason that they can recur.
Small lumps if they are not too troublesome can be left alone. Symptomatic ones can be treated by aspiration or puncture with a needle to disperse fluid and cause it to scar and heal. However there is a high recurrence rate.
The standard treatment for these cysts is surgical removal which is done under local anaesthetic.