Answer: Malignant melanoma

Histology: The tumor consists of cords and nests of round blue cells, often distorted by crush artifact. There is abundant pigment in the background. Immunostains showed that the tumor was positive for CD56, S100, Melan A, and HMB45, but negative for synaptophysin and chromogranin.

Discussion: In the sinonasal tract, there is a heterogeneous group of malignancies characterized by a population of undifferentiated cells with small to medium sized nuceli and minimal cytoplasm (the so-called small round blue cell tumors). Diagnosing them is made more difficult by the fact the biopsies from this region are often small, and frequently exhibit abundant crush artifact. The differential diagnosis is vast, and includes carcinomas (poorly differentiated squamous cell carcinoma, NUT midline carcinoma, SNUC, small cell carcinoma, and others), lymphoma, melanoma, and even sarcomas (rhabdomyosarcoma). The current case was submitted as “r/o esthesioneuroblastoma” on the basis of its small round cell appearance and CD56 positivity. However, CD56 is not specific, and should not be used by itself as evidence of neuroendocrine differentiation. Tip-offs for the diagnosis of melanoma in this case are the prominent pigment (which was Fontana-Masson positive, indicating it was melanin) and very prominent nucleoli. Additional immunostains confirmed the diagnosis of melanoma.

Malignant melanoma may be primary to mucosal sites, including the sinonasal tract. Unfortunately, most patients with mucosal melanoma of the head and neck present with advanced local disease, and the prognosis is poor.

Reference(s):
– McLean T, Tighiouart M, Muller S. Oral Oncol. 44(11):1039-46.
– Brandwein MS, Rothstein A, Lawson W, et al. Arch Otolaryngol Head Neck Surg. 123(3):290-6.