Slowly growing, painless mass in palmar aspect of the thumb. Cactus needle removed some months ago ? retained foreign body.
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Small (7 x 5 mm) solid mass deep to the epidermis within the subcutaneous fat. No abnormal vascularity on color Doppler.
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 color 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.