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1.History suggest most possible cause could be -
ganglion which arises from the joint space.
2.Could be from tendon, synovial,
nerve - most often after a trauma. Its pain less around the joint space. Other possibilities vascular pathology.
3.How ever
ultrasound will help to find out the nature of the lump ( solid , cystic,mixed) and source of the lesion and where all it is extending.
4.If any thing related to joint
MRI is excellent tool to evaluate the pathology.
5.So please wait for your scan - things should be clear after that. Good luck.
Hope i have answered your query.
Any thing to ask do not hesitate. Thank you.