Slowly growing, painless mass in palmar aspect of the thumb. Cactus needle removed some months ago ? retained foreign body
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Small, painless, apparently solid subcutaneous mass without blood flow could be a sebaceous cyst but an unusual location for such. It is associated with a history of previous puncture wound but no foreign body is identified on ultrasound and no abnormal blood flow on colour Doppler to indicate an inflammatory mass or granulation tissue.
This is an acquired condition that occurs as the result of implantation of epidermal fragments into the dermis by a penetrating injury. The epidermis continues to grow and forms a cyst lined with stratified squamous epithelium and filled with keratin.