An aspirate taken from a dog with a progressively enlarging skin mass.
Note the sheets of basaloid to squamous epithelium with fairly abrupt keratinisation.
The epithelial cells are very well differentiated and display little atypia (same nuclear size and shape etc.).
The keratin appears pigmented.
This is likely to either be a trichoepithelioma or an infundibular keratinising acanthoma i.e. a benign adnexal tumour.
A biopsy would be needed to rule out invasion and surgical excision is often beneficial as these lesions can rupture inducing a foreign body reaction (due to the extruded keratin).
First published: Wed, Dec 1 2010