Solitary giant trichoepithelioma presents as a large, polypoid lesion, usually in the lower trunk or in the gluteal area. Perform shave or small punch biopsy to allow a histologic diagnosis. In the upper dermis there are multiple nodules composed of uniform, basaloid cells, frequently with central, keratin-filled cysts. Peripheral palisading is present, but artefactual clefting is uncommon. The stroma is generally fibrous, with very little myxoid component.
Calcification is very common, typically associated with the rupture of the keratinous cysts.
The intervening stromal cells express CD34. Merkel cells can be detected in all trichoepithelioma variants. It occurs in the same population as the classic type and presents as a plaque located in the same anatomic areas as the classic form. Histologically, it shows narrow strands of tumor cells, a desmoplastic stroma, and keratinous cysts. Pleomorphism, palisading, or peripheral clefting are not seen.