The tumour usually begins as a small erythematous nodule which rapidly expands over 3-4 weeks. The final size is often 1-2 cm in diameter but occasionally, it may extend to 15 cm diameter. There is radial symmetry. Typically, resolution begins after about 6 weeks but this may be longer.
Exposed, hair-bearing skin is most commonly affected, particularly the face and the dorsum of the hands.
The lesion is characterised by a central keratin-filled crater, which forms a plug, encircled by a heaped-up shoulder of epidermis. The epidermis is stretched over the edge of the tumour and telangiectasia may be visible beneath the surface. A keratin horn may form.
Untreated, the lesion involutes over 2-3 months to leave an often irregular and pitted scar.
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