43. Seborrhoeic keratosis

Page created on May 8, 2019. Not updated since.

Staining: HE

Organ: Skin


A well-circumscribed skin lesion is visible.

The stratum corneum is thickened, meaning that there is hyperkeratosis. The cells of the stratum corneum have retained their nuclei, meaning that there is parakeratosis.

There are neutrophils in the stratum corneum. These are not related to the disease and are instead the result of the patient scratching the seborrheic keratosis, causing irritation.

The basal layer of the epidermis contains keratin cysts, called horn cysts. These are formed as the stratum corneum invaginates into the cellular layer of the epidermis, which is also visible on the slide.

There is acanthosis, which is visible as the presence of dermal cells in small nests inside the epidermis.

Diagnosis: Seborrheic keratosis


  • Unknown
  • Paraneoplastic (Leser-Trelat sign)


Sporadic seborrheic keratoses usually appear in elderly persons. If dozens of keratoses appear within a short period of time, it is a paraneoplastic syndrome called Leser-Trelat sign. This suggests an internal cancer, most commonly a GI tract carcinoma.

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2 thoughts on “43. Seborrhoeic keratosis”

  1. Hey greek.doctor/G-cobra
    Acanthosis is defined as diffuse epidermal hyperplasia.
    Then how come acanthosis in here is visible as the presence of dermal cells in small nests inside the epidermis.?


    1. Good question! I’m not sure acanthosis is always diffuse, and I know there are multiple types of it. I suspect it looks like this because of the cut, that these are actually papillae in cross-section or something.

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