F1Ch33a (N846): One group of follicular hamartomas is characterized by a prominent participation of the perifollicular mesenchyme. Perifollicular mesenchyme was included in the definition of the adventitial dermis; the papillary dermis is the other component of the adventitial dermis but perivascular mesenchyme and the stroma of sweat glands might also be included in the category. In this fibrofollicular hamartoma, the peri-follicular mesenchyme is a tumoral component; its interface with the reticular dermis is well defined - at the right hand edge of the field, a cleft defines this interface. In the plane of this section, the ostium of the parent follicle is represented(top of the field on the left). Thin strands of small squamous cells extend from the parent and, in turn, show branching patterns. Two of the strands terminate in a bulbous expansion in which a portion of the component cells are vacuolated in the pattern of the cells of the outer root sheath. In addition, there is a central component showing the pattern of the inner root sheath. A small hair shaft is cut in cross section. For some of the other branching components, the cells of a bulbous extremity show patterns of hair bulb differentiation with an associated papilla. For some of the extremities, the patterns have a catagen-like quality. It is as if the secondary components (i.e, those terminal branches manifesting patterns of the inconstant portion of a normal follicle) cycle in a manner that is independent of the phenomena of its neighbors.
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