Intermediate-grade meningeal melanocytoma associated with nevus of Ota: a case report and review of the literature

Abstract

Meningeal melanocytomas are rare melanin-producing tumors that are often found to be benign. However, a small subset of these tumors can present as intermediate-grade melanocytomas (IGMs) that have histopathological features that are between those of benign melanocytomas and malignant melanomas. IGMs have the potential to recur and metastasize or progress to a more histologically high grade melanoma. Melanocytomas appear to differ from primary and metastatic melanoma by their prolonged clinical course and they appear to have different driver mutations (i.e. mutation of GNAQ gene). The association of a meningeal melanocytoma with nevus of Ota is extremely rare. To our knowledge, there have been only 10 reported cases of synchronous occurrence and only one of the cases involved an IGM. We report the second case of intermediate-grade meningeal melanocytoma that is associated with congenital nevus of Ota. Histopathological work-up confirmed the intermediate grade of the lesion and a driver GNAQ mutation was identified consistent with previous reports.

Fig. 1

Dura with an adherent melanocytoma. A heavily pigmented neoplastic proliferation of spindled melanocytes growing in interlacing fascicles. Mitotic figures are only occasionally seen. Immunohistochemical stains were performed and demonstrated the tumor to be strongly immunoreactive for S-100, HMB-45 and Melan A (not shown) (hematoxylin and eosin, × 40).

Fig. 2

KI-67 immunostains demonstrate proliferative indices of 2–3% in the tumor. The KI-67 proliferation index is estimated as the percentage of positive tumor nuclei in the area of highest density and correlates with the paucity of mitotic figures observed.