||Since in keratoacanthoma the architecture of the lesion is as important as the cellular characteristics in establishing the diagnosis, it is advisable for the purpose of biopsy to remove either the entire lesion or at least a wedge extending from the center of the lesion and which includes one margin.
Characteristically, a keratoacanthoma is an exophytic superficial neoplasm which shows an abrupt transition between hyperplastic epithelial cells of the lesion and the surrounding normal epidermis. The hyperplastic epithelium of a keratoacanthoma extends like a "cup" around a central crater. In the early stages this central crater is filled with strands of atypical dyskeratotic keratinocytes with frequent mitoses. In the later stages, the keratinocytes of the central crater undergo maturation and keratinization, producing a keratin-filled central cavity. After reaching maturity the lesion gradually involutes, expelling the central keratin plug and leaving a thin puckered scar.
a larger and more mature keratoacanthoma, which has also arisen in the conchal bowl, shows a central crater filled with keratinous material and a deep surrounding cuff of hyperplastic epithelium.