Clinicopathologic Correlation

Clinical Feature

Pathologic Feature

"Stuck on" papule

Exophytic

Symmetric with easily defined border

Papillomatosis and acanthosis are symmetric with a sharp margin

Rough or velvety surface

Papillations with overlying thickened stratum corneum

Tan to brown to black

Hyperpigmentation of basalar keratinocytes, seen throughout epidermis in darker lesions

Keratin filled plugs

Pseudohorn cysts

Differential Diagnosis:

Seborrheic Keratosis

Verruca Vulgaris

Broad-more horizontal

High-more vertical

Papillomatosis (gentle)

Digitated (spiking)

Normal granular layer

Prominent granular layer

No koilocytes

Vacuolated koilocytes in superficial layers of epidermis

Basket-weave hyperkeratosis with scattered parakeratosis

Columns of parakeratosis above tips of digitations

No serum in horn

Serum often seen above digitations

Slightly dilated blood vessels in dermal papillae

Markedly dilated and tortuous blood vessels in dermal papillae

Pathophysiology: ■

Suspect autosomal dominant transmission Preliminary evidence to support a monoclonal or neoplastic origin versus polyclonal or hyperplastic May be derived from keratinocytes of the infundibulum of the hair follicle

References:

1. Nakamura H, Hirota S, Adachi S, et al. Clonal nature of seborrheic keratosis demonstrated by using the polymorphism of the human androgen receptor locus as a marker. J Invest Dermatol 2001; 116:506.

2. Kossard S, Berman A, Winkelmann R. Seborrheic keratosis and trichostasis spinosa. J Cutan Pathol 1979; 6:492.

SEBORRHEIC KERATOSIS, COMMON HISTOLOGIC VARIANTS

Variants:

■ Early, developing from a solar lentigo, pigmented, inflamed or irritated, hyperkeratotic, pedunculated, acanthotic, reticulated, clonal, melanoacanthoma.

Derived from solar lentigo; thin epidermis laterally with bulbous rete ridges, often hyperpigmented, gradual acanthosis, proliferation of small basaloid cells in strands, development of pseudohorn cysts (Fig. 2B) Pigmented; abundant melanin in keratinocytes throughout the epidermis. No significant increase in melanocytes (Fig. 2D)

Inflamed or irritated

■ Perivascular or lichenoid, predominantly lymphocytic inflammatory infiltrate in the dermis (Fig. 3B)

■ Gradual change from basaloid to more squamous differentiation (Fig. 3C)

■ Squamous eddies (whorls) often appear

■ Individual keratinocytes may have mild to moderate nuclear atypia (Fig. 3D)

Reticulated; thin, anastomosing strands of small, uniform basaloid cells extend into the dermis (Fig. 4A).

Clonal; intraepidermal nests or localized collections of very uniform basaloid or large squamous cells separated by ordinary basaloid cells (Fig. 4B). Melanoacanthoma

■ Acanthotic proliferation of basaloid keratinocytes (Fig. 4C)

■ Dendritic melanocytes sprinkled at all levels of the epidermis (Fig. 4D)

■ Melanin prominent in cytoplasms of melanocytes, not in keratinocytes

Clinicopathologic Correlation:

Clinical Feature

Pathologic Feature

Solar lentigo: macular tan border

Hyperpigmented bulbous rete

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