A case of localized follicular hamartoma: an ultrastructural and immunohistochemical study

Abstract

We report the case of a 22-year-old woman with a nevoid plaque that we termed localized follicular hamartoma. The plaque was noticed at puberty on a unilateral site of the face and scalp. Clinically, it revealed numerous, skin-colored to light brown papules alone and in groups, occasionally bearing a single hair. Histologically, branched epithelial nests of squamoid and/or basaloid cells were revealed in connection with the interfollicular epidermis and the upper portions of hair follicles, of which the lower portions showed normal structures. Immunohistochemically, the epithelial nests showed the keratin expression consisted with that of the infundibular epithelium. S-100-positive cells were found in the epithelial nests and the stroma. Factor XIIIa-positive dendritic cells were numerous in adjacent to the epithelial nests. Ultrastructurally, immature melanocytes with a small number of premelanosomes and Merkel cells were found in the nests. Stromal dendritic cells showed the adherent features of the cytoplasmic processes to anchoring fibrils or basal lamina of the epithelial nests. From these findings, our case is a hamartoma, which seems to be an abortive growth of secondary hair germs with a limited differentiation to the upper follicular portion.

Congenital localized basaloid follicular hamartoma: a case report and review of the literature

“…This patient had congenital BFH, but she had no family history of BFH. Only two similar cases were reported in the literature 10,11 but no Chinese case of BFH has ever been reported.…”

Linear Unilateral Basaloid Follicular Hamartoma Following Blaschko's Lines: Two Case Reports and Review of the Literature

“…Mehregan and Baker coined the term “basaloid follicular hamartoma” in 1985. Morohashi et al , based on ultrastructural and immunohistochemical studies, described BFH as an abortive growth of secondary hair germs with limited differentiation toward the upper follicular portion of the hair shaft.…”

“…Basaloid follicular hamartoma (BFH) is a rare follicular malformation with distinctive histopathologic patterns. A characteristic finding is the presence of branching cords and thin strands of undifferentiated anastomosing basaloid proliferations that arise from hair follicles and are embedded in a fibrous stroma , although basaloid follicular hamartomatous changes can be seen in a wide range of clinical situations: a congenital or acquired generalized type associated with systemic diseases, a localized linear and unilateral type, and a solitary plaque or nodular type . Carney reported the first case of linear and unilateral BFH in 1952, calling it linear unilateral basal‐cell nevus with comedones.…”

Basaloid follicular hamartoma

“…Recently, BFH was considered by Morohashi et al 6 . to be an abortive growth of secondary hair germs with a limited differentiation toward the upper follicular portion.…”