tumor of the follicular infundibulum

TUMOR OF THE FOLLICULAR INFUNDIBULUM

A solitary lesion from the left cheek of a 52 year old male.

This tumor was described by Mehregan and Buttler in 1961, and it is well-illustrated and discussed in common dermatopathology textbooks.

This is a simple follicular acanthoma having orientation that is predominately horizontal (plaque-like). This is in contrast with other simple follicular acanthomas having a significant vertical component such as inverted follicular keratoses and trichilemmomas. This type of horizontal orientation is also seen in seborrheic keratoses, and some regard seborrheic keratoses as tardive follicular hamartomas or acanthomas. It should be noted that that there are horizontally oriented, complex (combinations of follicular, sebaceous, and apocrine) acanthomas of the follicular apparatus having different names such as reticulated acanthoma with apocrine differentiation.

Reticulated or fenestrated architecture of epithelium resembling isthmic or outer root sheath epithelium is characteristic. A component of primordial follicular epithelium is uncommonly present to minimal degree. Prominent stromal participation is not a feature of this lesion as it has been described, but such a variant would be anticipated. The acanthotic epithelium usually is more eosinophilic and pale staining than the overlying epidermis. Peripheral palisading is present to varying degrees.

Scan power view of the biopsy. Notice the reticulated or fenestrated architecture of the acanthotic epithelium. The axis of proliferation is predominately horizontal or plaque-like. A small cyst is also noted, and this may or may not be part of the lesion.

Composite low power view. The hyperplastic epithelium is more pale and eosinophilic than the overlying epidermis. Pseudohorn cysts are present, but the fenestrated architecture and the contrasting epithelia are not of the type characteristic of a seborrheic keratosis.

Medium power view. Peripheral palisading is present. The epithelium resembles that found in the isthmus of a normal follicle. This also looks like the epithelium found in some trichilemmomas.

Reference:
Mehregan AH, Buttler, JD. A tumor of follicular infundibulum. Arch Dermatol 1961;83:924

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	Scan power view of the biopsy. Notice the reticulated or fenestrated architecture of the acanthotic epithelium. The axis of proliferation is predominately horizontal or plaque-like. A small cyst is also noted, and this may or may not be part of the lesion.
	Composite low power view. The hyperplastic epithelium is more pale and eosinophilic than the overlying epidermis. Pseudohorn cysts are present, but the fenestrated architecture and the contrasting epithelia are not of the type characteristic of a seborrheic keratosis.
	Medium power view. Peripheral palisading is present. The epithelium resembles that found in the isthmus of a normal follicle. This also looks like the epithelium found in some trichilemmomas.