Clinicopathological study of crateriform verruca: Crateriform epithelial lesions histopathologically distinct from...

Keratoacanthoma (KA) is a distinct clinicopathological entity, but it is often confused with other crateriform tumors. This study re-examined the clinicopathological features of 380 crateriform epithelial tumors with a central keratin plug. Seventy-six tumors (20%) had histopathological features that differed from solitary KA and were more verruca-like, and we designated these lesions as crateriform verruca (CFV). We performed clinicopathological re-examination of these neoplasms with a crateriform architecture and epithelial lip-like structures similar to KA, which also displayed histopathological features reminiscent of verruca vulgaris, such as finger-like exophytic projections with hyperkeratosis and acanthosis, focal hypergranulosis and arborization. Clinical data on CFV were also summarized. The main histopathological differences from KA were that CFV showed proliferation of keratinocytes with a similar size and regular arrangement, and the base of CFV was well demarcated without endophytic growth. Interestingly, some CFV were partly composed of epithelial cells with large pink cytoplasm in the upper malpighian layer between papillomatous projections. Furthermore, areas of trichilemmal-like keratinization without formation of the granular layer were seen in some lesions. These types of CFV were hardly distinguishable from KA, unless it is recognized that CFV may contain trichilemmal keratinization-like areas accompanied by large epithelial cells with eosinophilic cytoplasm. We have proposed the term CFV for these verrucous neoplasms to differentiate them from KA.