Seborrheic Keratosis: A Pictorial Review of the Histopathologic Variations

A brief review of the variations of microscopic appearances of seborrheic keratosis is presented. Figure 1 Seborrheic keratosis: Acanthotic type (Figure 1) Although no exact data are available for percentage distribution of different histologic subtypes of seborrheic keratosis, the acanthotic type appears to be the most common. This type shows marked acanthosis of predominantly basaloid cells [1]. Moderate papillomatosis and hyperkeratosis are present and characteristic horn cysts or pseudocysts are seen. Aproximately one-third of these lesions exhibit melanocyte proliferation and hyperpigmentation., demonstrating the common finding of overlapping histologic findings between different subtypes. Squamous eddies are absent. Figure 2 Seborrheic keratosis: Hyperkeratotic type (Figure 2) Pronounced papillomatosis is present in the hyperkeratotic form of seborrheic keratosis [1]. Acanothosis is mild, but shows a verrucous appearance with elongated projections (“church spire” pattern). There is pronounced orthohyperkeratosis. While horn cysts and pseudocyts may be seen, they are less common than in the acanthotic form. Hyperpigmentation is unusual. Figure 3 Seborrheic keratosis: Clonal type (Figures 3 and 4) Seborrheic Keratosis: A Pictorial Review of the Histopathologic Variations