The correct answer is inclusion cyst (choice “c”).
Inclusion cysts are also called traumatic inclusion cysts or implantation cysts and are quite distinct from “sebaceous,” epidermal, or epidermoid cysts. An inclusion cyst results from traumatic implantation of surface adnexal structures (eg, sebaceous glands) that continue to function, eventuating in the formation of an organized sac whose wall is composed of stratified squamous epithelium with a granular layer, no significant atypia, and surrounding pasty lamellated acellular keratin.
Hands are the most commonly affected area, although the precipitating puncture wound doesn’t have to be as impressive as this patient’s was. Nails and sewing needles can produce the same result.
The patient’s lesion was removed, at which point its pasty contents (a diagnostic clue) were revealed, and the wound closed. Although the absence of redness or tenderness helped to rule out some items in the differential (eg, felon, abscess), and the lesion demonstrated clear cystic features, the specimen was sent for pathologic examination for confirmation, since cancer would also belong in the differential for such a lesion.