Rippled-Pattern Trichomatricoma

The study described a unique hair matrix tumor, termed "rippled pattern trichomatricoma," found at the base of a solitary trichoepithelioma. This tumor exhibited an unusual arrangement of tumor cells, with alternating epithelial cords and hand-like stroma resembling Verocay bodies or "ripplemarks." Some areas showed a cribriform pattern due to myxomatous degeneration. The tumor contained dense melanin pigment and scattered Langerhans cells, as indicated by S-100 and GDI (OKT6) antigen stains. The majority of tumor cells were identified as immature pilar cortical cells, characterized by strong HKN-6 positivity, association with melanocytes, and ultrastructural features such as electron-dense tonofilaments and desmosomes. These cells transformed into semikeratinized cells without producing trichohyalin granules. The tumor also contained squamous eddy-like or horn pearl-like foci and large keratin-filled cysts, suggesting differentiation toward non-cortical cells. This entity was considered distinct from trichoblastoma due to its degree of differentiation.