If fine-needle aspiration is performed, the diagnosis of PM may be made only if all major components of PM are present in the aspirate, including calcium deposition, basaloid cells and keratinized ghost or shadow cells
Tumors are well-circumscribed, dermal to subcutaneous nodules composed of several components, including basaloid proliferation, shadow cells, dystrophic calcifications, and foreign-body giant-cell reactions (figure 1).
They have a high mitotic index, and they merge imperceptibly to abruptly with the keratinizing shadow cells.
The shadow cells have abundant eosinophilic cytoplasm and a negative space where the nucleus was once located (figure 2).
Finding follicular bulbs, papillary mesenchymal bodies, trichohyalin granules, hair shafts, shadow cells
, and focal CD34 staining in adjacent tumor stromal cells all favor benign entities.