Periocular keratoacanthoma: A clinicopathologic study and diagnostic challenges

Abstract Purpose: Keratoacanthoma (KA) is a cutaneous neoplasm that presents as a rapidly growing tumor on ultraviolet light-exposed skin. It appears as an exophytic, crater-like lesion filled with keratin. In periocular sites, the eyelids are most often affected. Clinically, diagnosis and distinction from squamous cell carcinoma can be difficult. This study aims to describe the histopathological features and epidemiological characteristics of a large series of KA to highlight its clinical and histopathological features. Patients, Materials, and Methods: Forty-nine cases from the MUHC-McGill University Ocular Pathology and Translational Research Laboratory (1997–2022) were reviewed to determine histopathological and epidemiological traits. Data on age, sex, clinical site, and histopathological features were extracted. Results: Among 49 cases, the average age was 65 years; 60% were male. Sites were upper eyelid 39% ( n = 19), lower eyelid 39% ( n = 19), canthus 8% ( n = 4), eyebrow 2% ( n = 1), and unspecified 12% ( n = 6). Histopathologically, all cases displayed a keratin-filled crater with epidermal acanthosis and hyperkeratosis and parakeratosis. Mild-to-severe atypia, up to carcinoma in situ (CIS), was found in 39% ( n = 19). Mitotic figures were present in cases with atypia. Extensive or focal actinic damage was identified in superficial and deep dermis in all cases. Most cases showed chronic, nongranulomatous inflammation. Conclusions: To the best of our knowledge, this is the largest cohort of eyelid KA. The presence of mild-to-severe atypia and CIS in a minority of cases did not indicate malignant transformation. Attention to patient age and lesion location may contribute to a correct clinical diagnosis in clinical practice and improve diagnostic confidence.