Case 75 - Discussion
Uploaded: 2007-11-30, Updated: 2007-12-01
Hyperkeratotic Seborrheic Keratosis
General Microscopic Features
of Seborrheic Keratosis
Raised above the skin surface, papillomatous epithelial proliferation containing horn cysts without any tendency toward malignancy. The proliferating cells are epidermal and have a basaloid appearance. The number of epidermal basal cells is greatly increased.
most frequent. A thick layer of basal cells is observed interspersed with pseudo-horny cysts. Invaginations to form keratin-filled pseudocysts are present. Some of these cells contain melanin.
pronounced hyperkeratosis and "church-spired" papillomatosis with less acanthosis. The epidermis is comprised largely of squamous cells interspersed with aggregates of basaloid cells.
Reticulated or adenoid type:
numerous thin tracts of basaloid epidermal cells that are branched and interwoven, less epidermal thickening, and
horn pseudocysts. Marked hyperpigmentation is often present.
may be confused with eccrine poromas, but no ductular differentiation is observed in seborrheic keratosis.
Irritated seborrheic keratoses:
spongiosis and mild acantholysis and squamous eddies. S
of flattened keratinocytes with a superficial resemblance to the "horn pearls" of squamous cell carcinoma.
In irritated seborrheic keratoses, pronounced squamous metaplasia can occur, which may be misdiagnosed as basosquamous carcinoma.
nverted follicular keratosis
: spongiosis and squamous eddies, with a distinctly endophytic growth pattern arrayed about a central keratin-filled invagination.
Clonal/nested seborrheic keratosis
: well-demarcated nests of basaloid or larger squamous cells within an acanthotic seborrheic keratoses.
Melanoacanthoma: a deeply pigmented seborrheic keratosis in which an acanthotic proliferation of large dendritic melanocytes is identified. It probably represents a concomitant proliferation or activation of the dendritic melanocytes and epidermal cells.
Lichenoid seborrheic keratosis: an inflammatory variant.
AFIP, nonmelanocytic tumors of the skin, series 4