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The Internet Journal of Dermatology 2009 : Volume 7 Number 2

Sebor rh eic Ker atosis: A Pictor ial Review of theHistopathologic Variations

Deba P Sar ma MD  

Department of Pathology 

Creighton University Medical Center

Omaha NE USA 

Susan Repertinger MD  

Department of Pathology 

Creighton University Medical Center

Omaha NE USA 

C i t a t i o n : D. Sarma & S. Repertinger : Seborrheic Keratosis: A Pictorial Review of the Histopathologic Variations. The Internet Journal

of Dermatology . 200 9 Volume 7 Number 2

Keywords: seborrheic keratosis | seborrheic keratosis variations | seborrheic keratosis microscopic images

 

Abstract

A brief review of the variations of microscopic appearances of seborrheic keratosis is presented.

 

 

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

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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.

 

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.

 

Seborrheic keratosis: Clonal type (Figures 3 and 4)

 

The hallmark of the clonal (nested) seborrheic keratosis subtype is the proliferation of sharply demarcated

intraepithelial nests of basaloid or pale cells (Borst-Jadassohn phenomenon). In some cases the nests are composed of 

larger cells with conspicuous intercellular bridges, with nests separated by strand of cells with small dark nuclei.

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Seborrheic keratosis: Flat clonal type (Figures 5 and 6)

 

Flat seborrheic keratosis of clonal type shows acanthosis and intraepithelial nests of basaloid or pale cells. However,

papillomatosis and hyperkeratosis is not prominenent. This variant may be confused histologically with melanocytic

nevus or malignant melanoma by the inexperienced.

 

Seborrheic keratosis: Reticulated type (Figures 7 and 8)

 

The reticulated (or adenoid) type is characterized by numerous, thin, double rows of basaloid epidermal cells which

extend from the epidermis and show branching and interweaving in the dermis. Hyperpigmentation is relatively 

common, although horn cysts and pseudocysts are not [1]. There is clinical and histologic evidence of a relationship

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between solar lentigo and the reticulated subtype of seborrheic keratosis; solar lentigo may even become a reticulated

seborrheic keratosis through exaggerated downward budding of basal cells.

 

Seborrheic keratosis: Irritated type (Figures 9 and 10)

 

Irritated seborrheic keratosis shows a lichenoid inflammatory infiltrate in the dermis and intraepithelial squamous

eddies [1], which are composed of whorling aggregates of eosinophilic squamous cells. In this type, the squamous cells

outnumber the basaloid cells. Most eddies appear to show at least one of the morphological features of intraepidermal

hairr follicle structures [2]. Squamous eddies may be confused with horn pearls of squamous cell carcinoma, but can be

differentiated from them by their large number, small size, and circumscription. Other features of irritated seborrheic

keratosis include apoptotic cells in the basal layer and occasional acantholysis, dyskeratosis, and spongiosis.

 

Seborrheic keratosis: Pigmented type (Figures 11 and 12)

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Pigmentation is often seen within the acanthotic and reticulated subtypes of seborrheic keratosis. Pigment is present

mainly within basal keratinocytes, although in melanoacanthoma, a rare type of pigmented seborrheic keratosis, a

marked increase in melanocytes containing melanin pigment is seen. The pigmented subtype may be clinically 

confused with other pigmented lesions, such as malignant melanoma, pigmented basal cell carcinoma, or melanocytic

nevus.

 

Seborrheic keratosis: Acantholytic type (Figures 13 and 14)

 

The acantholytic subtype usually incorporates features of other subtypes, particularly of the irritated type, and are

located on the face and scalp (65%) [3]. Acantholysis is seen almost exclusively in the squamous nests showing

dyskeratosis and spongiosis between and around squamous eddies or horn cysts. It is speculated that the

dyskeratotic, degenerative changes of keratinocytes, together with the spongiosis, are responsible for the acantholysis.

Correspondence to

Deba P Sarma, M.D.

Department of Pathology 

Creighton University Medical Center

Omaha, NE, USA 

debasarma@creighton.edu

References

1. Hafner, C. and T. Vogt. Seborrheic keratosis. J Dtsch Dermatol Ges, 2008. 6(8): 664-77. (s)

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2. Choi HJ, Yun SK, Kim HU, Ihm CW. Squamous eddies in irritated seborrheic keratosis. Am J Dermatopathol 2007.

29(1): 28-31. (s)

3. Chen M, Shinmori H, Takemiya M, Miki Y. Acantholytic variant of seborrheic keratosis. J Cutan Pathol 1990. 17(1):

27-31. (s)

4. Lever’s Histopathology of the Skin, Elder DE, Editor, 10th Edition, 2008 by Lippincott Williams and Wilkins. (s)

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