Trichilemmoma: Cell Biology of the Normal Human Outer Root Sheath

The study reviewed the cell biology of the outer root sheath (ORS) in normal human hair follicles, focusing on the anagen phase. It described the differentiation and keratinization processes of the ORS, noting that the inner cell layer forms the innermost ORS layer and keratinizes with keratohyaline granules, while the outer layer increases in cell number and keratinizes without these granules. The basal lamina thickens during anagen and degenerates in catagen. The ORS cells around the club hair root lack glycogen and keratohyaline granules. The study also compared the cell characteristics of trichilemmal tumors to normal ORS, finding some similarities but many differences.