The pilomatricoma (pilomatrixoma) is a peculiar, distinctive benign tumor. In this case of a 68-year-old woman, the clinician suspected a squamous cell carcinoma. This case is slightly unusual, because they typically appear in childhood. The head and neck is a common location, however. This lesion is thought to have a primitive follicular origin showing matrical differentiation. Malignant transformation is rare. These lesions are relatively straightforward to diagnose as few lesions show the combination of germinative epithelium admixed with "wet keratin", or keratinizing ghost cells. This phenomenon is also seen with craniopharyngiomas. In some lesions (usually with increasing age of the lesion), only the wet keratin is present, often with an associated foreign-body giant cell reaction. Pigment, calcification, and ossification can also be seen.
Histologic sections of skin show a dermal tumor with a heterogeneous appearance. It is well circumscribed and consists of basophilic cellular nodules mixed with eosinophilic extracellular material.