To the Editor.—
Pilar sheath acanthoma, a type of follicular hamartoma, typically presents as an asymptomatic, small, solitary papule, often with a central opening, on the face (especially the upper lip) of adults. Recently, we have had the opportunity to review sections from eight such lesions, and have found several histologically constant features, including a widely dilated infundibulum plugged by cornified cells (Fig 1), numerous elongated epithelial aggregates emanating from the infundibular undersurface, and an inconspicuous fibrous stroma. In particular, the epithelial aggregates are characterized by the following: (1) many tiny keratinous cysts of two distinct types: (a) infundibular cysts ("epidermal" cyst-like), with flattened lining cells possessing prominent keratohyalin granules. We designate these infundibular because the lining cells of the normal follicular infundibulum possess these attributes. (b) isthmic cysts (Fig 2) ("trichilemmal" cystlike), whose lining cells are plump, with abundant, pale-staining cytoplasm, often devoid of keratohyalin granules. The appellation isthmic
Lee JY, Hirsch E. Pilar Sheath Acanthoma. Arch Dermatol. 1987;123(5):569. doi:10.1001/archderm.1987.01660290033010
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