TUMOR HAVING SOME OF THE FEATURES OF A TRICHOFOLLICULOMA
The classical trichofolliculoma is a highly differentiated follicular tumor within which inner and outer root sheath differentiation are present. That tumor also has distinctive architecture. Follicular tumors having a lesser degree of differentiation but with the same type of architecture are occasionally encountered, and this is such an example. This tumor is presumably benign.

From the face of a 74 year old male:
 
Scan power view. Primitive follicular units radiate into a central infundibular cavity. This is similar to the architecture of a trichofolliculoma in which the follicular components radiate into a central cyst having infundibular differentiation.
Medium power view of the left side of the lesion. A structure having the epithelial and connective tissue features of a hair bulb is seen in the 9:00 o'clock position. Fibroblastic stroma of the type found in trichoepitheliomas is also present. The epithelium having more eosinophilic cytoplasm is of infundibular or outer root sheath sheath type.
A high power view of the central aspect of the superficial part of the lesion. The arrowhead points to a sebocyte (SC). Participation by the sebaceous component of the pilosebaceous unit is not unexpected. Keratohyalin granules of the infundibulum are commonly very prominent is follicular tumors and not presumptive evidence of viral etiology.

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