Pathology of Keratoacanthoma - Dr Sampurna Roy MD.

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Dermpath-India

Pathology of Keratoacanthoma

Dr Sampurna Roy MD

Keratoacanthoma was first described in 1889 by Jonathan Hutchinson.

He described the lesion as 'crateriform ulcer of face'.

Keratoacanthoma is a controversial cutaneous tumour that usually occurs in elderly patients.

Males are more often affected than females.

Keratoacanthomas often occur spontaneously as a single rapidly growing tumour on sun-exposed skin.

Multiple keratoacanthomas are rarely seen.

Keratoacanthomas may also develop after trauma, laser resurfacing, radiation therapy, and at the donor site after skin grafting.

This lesion grows rapidly to the size of 1-2 cm over a period of one to two months and tend to resolve spontaneously after several weeks to months leaving an atrophic scar.

Macroscopic features:

The lesion presents as solitary nodule with a central keratin plug.

Microscopic features:

Keratoacanthoma is an exoendophytic, symmetrical lesion characterized by deep bulbous lobules of keratinizing well differentiated squamous epithelium with central keratin filled crater.

There is marked acanthosis with hyperkeratosis and little or no parakeratosis.

In early lesions there is marked atypia and mitotic figures on the base of the lesion.

Cells in the centre of the tumour have a "glassy" appearance.

There is lipping of edges of normal epidermis that extends over the central keratinous crater.

Prominent inflammatory cell infiltrate is present around the lesion.

This tumour does not extend below the level of sweat glands.

The regressing lesion is characterized by loss of crateriform appearance, band of fibrosis, granulomatous infiltrate, and less cytological atypia.

Perineural and vascular invasion may be present.

Microabscesses are common at the advancing edge of these lesions.

Differential diagnosis:

The histologic differential diagnosis of keratoacanthoma is principally with well differentiated squamous cell carcinoma.

The following features favour the diagnosis of keratoacanthoma over squamous cell carcinoma.

- Rapidly growing lesion with a characteristic low power appearance of a crateriform lesion with central keratinous plug.

- Cytological pleomorphism is less common.

- The cytoplasm has a glassy, pale eosinophilic appearance.

- There is an abrupt transition between the lesion and adjacent epidermis and a sharp outline between the tumour nests and stroma.

- Absence of stromal desmoplasia.

- Presence of intraepithelial elastic fibres and intracytoplasmic glycogen.

Rare variants:

- Giant keratoacanthoma ;

- Keratoacanthoma centrifugm marginatum (multinodular keratoacanthoma);

- Subungual keratoacanthoma ;

- Multiple Keratoacanthoma.