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Pathology of Seborrheic


"Common epidermal tumour composed of

predominantly basaloid keratinocytes"

Path Case 95: Case history and images:

Diagnosis: Seborrheic Keratosis




Seborrheic keratosis is a very common cutaneous lesion characterized by epidermal proliferation and composed of basaloid cells admixed with some squamoid cells.

Clinically, these are often multiple lesions occuring in any part of the body except palms and soles. 

Common sites include trunk, arms and face in middle aged or elderly patients.

In characteristic cases the lesions are warty in appearance, brown to nearly black, sharply demarcated. The lesion may look as if "stuck on" to the skin.

Histological patterns: 

The tumour shows an elevated area of acanthotic epidermis associated with papillomatosis, hyperkeratosis and invaginations forming horn cysts.

The tumour is usually symmetric at the level of the adjacent epidermis.

There is an exophytic expansion. It is composed of broad interconnecting bands of cells containing the horn cysts.

The tumour cells are similar to the basal cells of the epidermis and are called "basaloid" cells.

Squamous cells form the other cellular component and are present in varying numbers.

Hyperpigmentation of the basal layer is common.

Based on architectural patterns seborrheic keratosis may be acanthotic, hyperkeratotic, reticular or verrucous forms.

Within these general architectural patterns there are various growth patterns which may be uniform or mixed in any individual lesion. These include monomorphous, pleomorphic, clonal, fascicular and acantholytic.

The following are the microscopic images and diagrams of the various types of seborrheic keratosis:


Acanthotic (solid):  Broad columns and sheets of basaloid cells with horn cysts.

Reticulated (adenoid): Interlacing thin strands of basaloid cells enclosing small horn cysts.


Hyperkeratotic (papillomatous): Exophytic lesion with hyperkeratosis, papillomatosis and acanthosis.

Clonal:  Intraepidermal nests of basaloid cells resembling Borst-Jadassohn phenomenon.

Irritated: The irritated lesions may show considerable squamous cell proliferation that may mimic squamous cell carcinoma.

There is a dense lichenoid inflammatory infiltrate predominantly of a lymphocytic nature.

Squamous eddies and apoptotic cells may be present.

Incidental focal findings include:  Trichilemmal differentiation, sebaceous differentiation and amyloid deposition.


Leser-Trélat is a rare paraneoplastic sign that is characterized by the sudden eruption of multiple seborrheic keratoses, associated with underlying internal malignancies.

Similar non-malignancy-associated multiple seborrheic keratoses eruptions are referred to as the "pseudo-sign of Leser-Trélat".


Further reading:

Vulvar Seborrheic Keratosis: Is There a Relationship to Human Papillomavirus?

Expression of Lumican in Hidroacanthoma Simplex and Clonal-Type Seborrheic Keratosis as a Potent Differential Diagnostic Marker.

Are all seborrheic keratoses benign? Review of the typical lesion and its variants.

Seborrheic keratosis with basal clear cells: a peculiar microscopic mimic of melanoma in situ.

Serpiginous seborrhoeic keratosis: an unusual presentation following an eczematous dermatitis.

Seborrheic keratosis of the external auditory canal in a 1-year-old boy.

Seborrheic keratosis: reflectance confocal microscopy features and correlation with dermoscopy.

Epidermal growth factor receptor expression in mice skin upon ultraviolet B exposure - Seborrheic Keratosis as a coincidental and unique finding.

Seborrheic keratosis with basal clear cells: a distinctive microscopic mimic of melanoma in situ.

Differentiation of hidroacanthoma simplex from clonal seborrheic keratosis--an immunohistochemical study.

The diagnostic yield of histologic examination of seborrheic keratoses.

Sign and pseudo-sign of Leser-Trélat: case reports and a review of the literature.

Sign of Leser-Trelat.

Differentiation disorders of keratinocytes in seborrheic keratosis (acanthotic type).

Histologic aspects of seborrheic keratosis.  

Seborrheic keratosis with focal acantholysis.

Trichilemmal differentiation in seborrheic keratosis.






Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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