Cystic trichoblastoma (so-called trichoblastic infundibular cyst): a report of three new cases.

Three cases of so-called trichoblastic infundibular cyst are reported. The lesions showed a configuration similar to infundibular cysts, including basophilic orthokeratotic corneocytes arranged in basket-weave pattern and intermingled with eosinophilic sebum. The cyst wall was mainly composed of stratified squamous epithelium showing infundibular keratinization throughout a granular layer. However, in some areas, epithelial cords, buds and reticulated proliferations of follicular germinative cells surrounded by a densely cellular stroma emanated radially from the cyst wall. In one case, in addition to the presence of follicular germinative cells, there were also aggregations of matrical cells with evidences of inner sheath and matrical differentiation. In our opinion, these findings support a neoplastic rather than a cystic nature for this lesion. We discuss the histopathologic differential diagnosis with other follicular cystic lesions showing similar keratinization.