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.
At higher magnification, nests of basaloid cells are interrupted by brightly eosinophilic globules. The same material forms a border around each lobule. The cells are fairly monotonous, although there is a hint of 2 populations, one more basaloid. Cytologic atypia is not appreciated. Ductules are easily found (not in this field, however).