TRICHOFOLLICULOMA
Multiple, tiny,  rather complete, follicular subunits insert into a central space that is lined by infundibular type epithelium. Sebaceous units occur  uncommonly. If the subunits are actively trichogenic, tiny hair shafts are produced and result in the characteristic clinical finding of a tuft that protrudes above the papule or nodule. Trichofolliculomas differ from traditional trichoepitheliomas by virtue of the number of follicular components represented and by the architecture of the lesion. There are tumors that must arbitrarily be assigned to one group or the other.

This 17 year old patient developed a dome shaped nodule in the scalp about 4 years ago. A tuft of tiny, white hairs protrudes from the surface.
 
 This clinical photo  was kindly provided by Dr. Bradley Summers. The arrowhead points to the tuft of tiny, white hairs.
Scan power view. The rectangle is the area from which the medium power pictures (below) were taken. A central space is lined by squamous epithelium consistent with infundibular epithelium. Tiny follicular subunits insert into the wall of the space.
A medium power view from near the lumen. This is the part of a subunit that inserts into the infundibular space. Arrowheads point to tiny hair shafts.
A medium power view of the more proximal parts of the follicular structures. Hair bulbs, specialized stroma plus inner and outer root sheaths are demonstrated.

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