This 64-year-old woman presented with a 6 mm papule on her scalp. The clinician submitted the specimen as basal cell carcinoma vs adnexal tumor vs amelanotic melanoma. Cylindromas often occur on the scalp as in this case. Rare malignant cases have been reported. The histology in this case is also typical with a characteristic mosaic, or jigsaw puzzle, pattern. The histology is usually diagnostic, but occasional cases may resemble spiradenomas.
Histologic sections of skin show a proliferation of basophilic lobules within the dermis. The lobules mold together in a jigsaw puzzle configuration. Brightly eosinophilic material borders the lobules and coexists with the basaloid cells. The lesion is fairly well circumscribed.