- Author: Michael S Howard, MD; Chief Editor: Dirk M Elston, MD more...
Following surgical excision, these tumors are found to consist of a dilated primary follicle lined by infundibular, stratified squamous epithelium and opening to the skin surface.
From the central follicle outward, numerous secondary and tertiary follicles can be observed, presenting at various levels of hair-follicle differentiation. Hair structures may be observed within the hair follicle lumen; small sebaceous elements may be found within the follicular units.
Minimal lymphocytic or granulomatous inflammation may be present. An abundant connective tissue stroma is also present surrounding the follicular structures.
Abundant Merkel cells have been demonstrated within the follicular epithelium, supporting the concept that trichofolliculomas are hamartomas.
A variant of the trichofolliculoma is the sebaceous trichofolliculoma, featuring similar histologic features, except for the presence of numerous well-differentiated sebaceous lobules emptying into the central, dilated primary follicle. Sebaceous trichofolliculoma demonstrates histologic overlap with folliculosebaceous cystic hamartoma.[8, 9] Some consider the latter tumor to be a sebaceous trichofolliculoma in telogen phase. A single case of trichofolliculoma with perineural invasion has been reported in the literature.
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