Thanks for posting your query.
Well, without a clinical evaluation it would be difficult to determine the cause of the lump.From description it seems a ganglion cyst
over your wrist.
I would suggest getting this evaluated by an orthopedician for an accurate diagnosis and appropriate management. You may get the X-ray of the area affected and FNAC (fine needle aspiration cytology) of lump under his/her guidance.
I hope this is helpful to you.
You can consult me again directly through my profile http://www.healthcaremagic.com/doctors/dr-saurabh-gupta/64132
Dr Saurabh Gupta.