Trichoblastoma, syringocystadenoma papilliferum, desmoplastic trichilemmoma and tumor of the follicular infundibulum with signet-ring cells, all arising in nevus sebaceus.

Herein, we describe a 63-year-old male with multiple tumors arising within a nevus sebaceus on the posterior scalp. On histopathologic examination, four distinct tumors were identified: trichoblastoma, syringocystadenoma papilliferum, desmoplastic trichilemmoma and tumor of the follicular infundibulum (TFI). Within the TFI component of the nevus sebaceus, there was intracytoplasmic accumulation of eosinophilic keratin, as shown on pancytokeratin-stained sections, imparting a signet-ring appearance to the cells. To our knowledge, this is the first report of signet-ring cells arising within a TFI occurring in a nevus sebaceus. We discuss this case as well as review the literature on multiple tumors arising within nevus sebaceus and signet-ring cell changes in primary cutaneous tumors.