REPORT OF A CASE
A 63-year-old white man was referred to the dermatologic surgery unit with a 1.5-cm-diameter firm, hyperkeratotic, crusted nodule on the dorsal aspect of his forearm (Figure 1). He denied any inciting trauma and stated that the nodule had developed as a crusted, bleeding lesion that had slowly enlarged over 6 months. The clinical diagnosis was that of a keratoacanthoma or squamous cell carcinoma. The lesion was completely excised and sent for histopathologic examination (Figure 2 and Figure 3).What is your diagnosis?DIAGNOSIS: Keratoacanthomalike pilomatricoma.
Histologic examination revealed a well-circumscribed, exoendophytic neoplasm characterized by a multilocular crater lined by two types of epithelia. At the periphery, "lips" of normal epidermis were present. In some foci, the crater was lined by squamous epithelium with basket weave keratinization. In other foci, there were nodular aggregates of basophilic cells (Figure 2). Basophilic cells showed scanty cytoplasm, vesicular nuclei, some mitotic figures, and transition to shadow cells (Figure 3). In the crater, there were aggregates of basket weave cornified cells intermixed with larger aggregates of shadow cells, some of which were partially calcified. At the base of the lesion, there were fibrosing granulation tissue and some aggregates of shadow cells surrounded by granulomatous inflammation.
Faust HB, Clark RE, Kamino H. Hyperkeratotic Nodule. Arch Dermatol. 1996;132(5):577-578. doi:10.1001/archderm.1996.03890290111015