Pilar Sheath Acanthoma
David Cassarino, MD, PhD
Key Facts
Terminology
Pilar sheath acanthoma (PSA)
Mature adnexal proliferation composed of thickened epithelium with enlarged pale-staining keratinocytes
Clinical Issues
Usually in middle-aged to older adults
Most often occur on upper lip
Slow-growing, stable lesion
Keratotic papule with central pore-like area
Microscopic Pathology
Endophytic, lobular proliferation of enlarged, mature squamous cells with prominent acanthosis
Usually superficial, well circumscribed, and noninfiltrative
Lobules typically surround a follicular structure
Foci of infundibular-type keratinization
Cells show abundant pale eosinophilic to clear-staining cytoplasm and small nuclei
 Scanning magnification of a pilar sheath acanthoma shows a dilated follicular structure lined by a thickened squamous epithelium with endophytic, lobulated areas  . |
 Higher magnification of the lobular areas shows acanthotic squamous epithelium with peripheral palisading  and scattered clear-staining cells  . |
TERMINOLOGY
Abbreviations
Pilar sheath acanthoma (PSA)
Definitions
Mature adnexal proliferation composed of thickened epithelium with enlarged pale-staining keratinocytes
ETIOLOGY/PATHOGENESIS
Unknown
No known causes/associations
CLINICAL ISSUES
Epidemiology
Incidence
Rare lesions
Age
Usually occur in middle-aged to older adults
Gender
Males and females equally affected
