Osteonevus of Nanta-A Rare Case Report of a Cellular Blue Nevus with Ossification.

Background and Clinical Significance: Osteonevus of Nanta is a rare histological phenomenon characterized by bone formation within a benign melanocytic nevus, most commonly in intradermal nevi of the head and neck. Although osteonevus of Nanta is rare, ossification in a cellular blue nevus is even more uncommon. To date, only one case of a cellular blue nevus with ossification has been documented. This case report adds to the limited literature and emphasizes the clinical importance of recognizing this rare phenomenon, as osteonevus of Nanta has been potentially associated with malignant melanoma. Case Presentation: A 72-year-old woman presented with an asymptomatic, pigmented scalp lesion that had recently increased in size. On clinical examination, the tumor appeared as a well-demarcated, firm, and nodular mass with dark blueish to violet pigmentation that measured 15 × 12 × 7 mm. To ensure a definitive diagnosis and rule out malignancy, the lesion was excised with narrow margins. Histological examination revealed a cellular blue nevus with prominent osseous metaplasia. Due to the absence of clear margins, a wider re-excision was performed. No residual tumor was found, and the patient remained asymptomatic with no recurrence. Conclusions: This case represents only the second published example of a cellular blue nevus with ossification. While osteonevus of Nanta is benign, its potential association with malignant melanoma, as well as its clinical resemblance to malignant entities such as nodular melanoma, malignant blue nevus, and pigmented basal cell carcinoma, underscores the need for thorough clinical and histopathologic evaluation.