Intracytoplasmic eosinophilic inclusion bodies with embryonic folliculosebaceous-apocrine unit differentiation in syringocystadenoma papilliferum.

We describe a case of syringocystadenoma papilliferum (SCAP) with a unique histopathology. A 50-year-old Japanese woman presented with a pedunculated tumor in the pubic region. Histopathological examination showed that the tumor was composed of basaloid cell proliferation interconnecting from the epidermis to the dermis. Ductal structures in the tumor were lined by club-shaped columnar cells with apical snouts. Interestingly, numerous vacuolated cells with hyaline globule-like cytoplasmic inclusions were present among the columnar cells, the content of which was identified as sialomucin. Electron microscopy revealed that the vacuolated cytosol of luminal cells represented intracytoplasmic lumens with a structure similar to embryonic apocrine ducts. We assumed that this case represents a rare variant of SCAP that had differentiated toward the embryonic folliculosebaceous-apocrine unit.