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Case Reports

Abstract

Congenital melanocytic nevi (CMN) are usually benign tumors developing in utero and present at birth. Their diagnosis can be complicated by histological atypia or heterogeneous differentiation. We present a unique case of a 3-week-old neonate with a 7 cm red/purple scalp CMN with hair growth showing heterogeneous areas concerning for evolving melanoma within a giant congenital nevus (GCN). Histopathologic examination showed extensive dermal replacement by small nests of spindle cells in a fibrillar matrix, with increased vessels and clusters of small round melanocytes interspersed between collagen bundles and around epithelial adnexal structures. The lesion also exhibited pagetoid arrays of melanocytes in both single cells and round nests, with pale, vacuolated cytoplasm and dusty melanin, overall mimicking superficial spreading melanoma. These features were consistent with a GCN with Schwannian differentiation (Nodular proliferative neurocristic cutaneous hamartomas (NCH)) in conjunction with a compound atypical melanocytic proliferation, highlighting the complexity of the lesion. A literature review highlights the importance of diagnosing NCH in GCN. Typically, NCH in GCN follows a benign course and may regress spontaneously. Only one case had multiple aberrations similar to a melanoma arising in CMN. More recently, lesional cells have been demonstrated to be PRAME-negative, supporting a benign diagnosis and arguing against melanoma. This unique case highlights the diagnostic challenges of heterogeneous differentiation within GCN in young children. Detailed histological, immunohistochemical, and sometimes molecular studies are essential in distinguishing these rare benign lesions from malignant melanoma, emphasizing the importance of knowledge of these lesions in this age group.