Clinical history: 30 year-old female with several pink dermal nodules on the scalp ranging in size from 0.5-1 cm.
What is the most probable diagnosis?
This is one of the most common benign adnexal tumors. They typically occur in the head and neck and scalp as a slow growing and sometimes painful solitary pink or red dermal nodule, although linear arrangements are also documented.
They average about 1 cm in size and there is a marked female predominance, usually appearing in early adulthood. Unfortunately the scalp lesions can grow to a large size and coalesce together to form what is known as a "turban tumor".
Histologically, they are non encapsulated lesions located in the upper dermis. They lack connection to the overlying epidermis.
A "jigsaw" or "mosaic" pattern is characteristic of the tumor lobules, with each lobule surrounded by a thick outer hyaline PAS positive basement membrane.
At the periphery of the lobules you will find small cells with scanty cytoplasm and hyperchromatic nuclei. In the centre you can identify larger cells with pale cytoplasm and an oval vesicular nucleus. Often, ductal lumina are present.
Immunohistochemically the epithelial cells express CK6, CK19, CK7 and EMA, as well as SMA and s-100 (myoepithelial differentiation) and IKH-4 (eccrine tumor).