Porokeratotic eccrine ostial and dermal duct nevus. An abnormally keratinizing epidermal invagination or a dilated, porokeratotically plugged acrosyringium and dermal duct?

Porokeratotic eccrine ostial and dermal duct nevus (PEODDN) has been said to represent a widely dilated, keratin-plugged acrosyringium and dermal duct. We have observed in a case of congenital PEODDN a normal-appearing, acrosyringium-like duct that traverses vertically the entire length of the parakeratotic column. Also, in its lower course, it stained positively for carcinoembryonic antigen, while the inner borders of the invagination from which the parakeratotic column arose stained negatively. This leads us to suggest that the epithelial structure in PEODDN is an abnormally keratinizing epidermal invagination through which an acrosyringium-like duct traverses, rather than an abnormally dilated, parakeratotically plugged acrosyringium and dermal duct.