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Case Reports

Abstract

Neurocristic hamartoma (NCH) is a pigmented cutaneous lesion originating from aberrant neural mesenchyme development. The lesion is composed of neural crest cells, including nevomelanocytes, Schwann cells, and pigmented dendritic and spindled cells. These tumors present a diagnostic challenge due to similarities with melanocytic lesions. We present a female in her 20s with a 1-cm smooth pedunculated plaque on the occipital scalp that had been present since birth. The lesion was biopsied, and histology demonstrated a combined intradermal nevoid and spindled cell proliferation with components of nevomelanocytes and pigmented spindled cells with a dendritic morphology. Immunohistochemistry exhibited positivity for SOX-10, MART, and HMB-45.  BAP-1 and p16 were preserved. Beta-catenin showed cytoplasmic staining. Lesional cells were negative for PRAME and demonstrated a low rate of mitotic activity and low Ki67 index (1-3%). FISH testing yielded negative results for copy number aberrations in RREB1, c-MYC, CDKN2A/2B and CCND1 loci. Due to similarities between NCHs, blue-type melanocytic neoplasms and congenital nevi, targeted panel next generation sequencing (NGS) was performed and was negative for mutations in common melanocytic neoplasm-related genes, including BRAF, NRAS, HRAS, GNAQ, GNA11, NF1, promoter TERT, and common kinase fusions. Given the histologic features and molecular findings without any common melanocytic neoplasm-related gene mutations, the patient was diagnosed with a neurocristic hamartoma. It is important for dermatologists and dermatopathologists to be aware of this entity and how it can be differentiated from melanocytic neoplasms. This case highlights the utility of NGS, histology, and immunohistochemistry in differentiating NCH from melanocytic neoplasms.