Thanks for sending this picture.
Yes you are very right it doesnot look like a xanthoma. It seems like soft tissue swelling and needs to be examined and investigated by a doctor directly because in such swellings the diagnosis is clinical.
Differentials include a lipoma, a sabecous cyst a muscular lump due to an un noticed trauma etc. I understand that development overnight is not seen with these diagnosis but variations do exist. It might need an ultrasound and least likely FNAC to be done .
I hope this helps you.
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