Answer

Dermal duct tumor

Review of literature

Dermal duct tumor (DDT) is a benign tumor of the intradermal portion of the eccrine sweat ducts and was first described by Winkelmann and McLeod in 1966 as a distinct tumor. ^[1]

It is now considered as a histopathological variant of poroma[2] where tumor islands are confined to dermis and no connection with the epidermis is seen.

Clinically, it has non-specific appearance and presents as flesh colored or reddish papules or plaques of size ranging from a few millimetres to 2 cm. It is commonly seen on the head and neck, but can also occur on the extremities and trunk. ^{[1, 3, 4]} Clinically, it may resemble a dermal nevus, achrocordon, sebaceous adenoma, dermatofibroma and other adenexal tumors and can be differentiated on histological examination. ^[1,3]

Microscopically, ^[5,6] DDT shows intradermal masses consisting of poroid and cuticular cells in varying proportion. Poroid cells form a dominant population. Poroid cells have round basophilic nucleus, scant cytoplasm and appears dark, while cuticular cells have large amount of cytoplasm and appears pale. The duct formation usually occurs in the areas of cuticular cells. Some tumors may show few clear cells, which have a vacuolar appearance of the cytoplasm, due to large amount of glycogen material. It has been suggested that the poroid cell, which forms the major population of poroma can differentiate into cuticular and clear cells. ^[5]

Four histopathological variants of poroma have been described viz hidroacanthoma simplex (HS) (intraepidermal poroma), poroma, DDT and poroid hidradenoma (PH). ^[5,6] Histologically, all these variants in common have poroid, cuticular and clear cells in varying proportions with some differences. HS is purely intraepidermal collection of the neoplastic cells. A poroma is connected to the epidermis and extends into the dermis, as cords and broad columns, while PH is present in the dermis and has a solid-cystic appearance. Occurrence of more than one variant in a single lesion has been reported. ^[5]

The ductal lining of apocrine and eccrine ducts are indistinguishable from each other. Earlier, poroma was considered to be of eccrine origin and designated as eccrine poroma, but currently, due to evidence of sebaceous and follicular differentiation in some cases, it is believed to have both eccrine and apocrine origin. ^[7]

Histochemistry of the tumor demonstrates staining for phosphorylase, periodic acid-Schiff (PAS), adenosine triphosphatase, succinic dehydrogenase, cytochrome oxidase, and keratin. ^[3,5]

Simple surgical excision is recommended and recurrence is rare, following complete removal. ^[8]

The Winners of this Quiz are:

1. Shenoy M.V., Bangalore

2. Rameshwar M. Gutte, Mumbai