• Arnaud Uguen, Camille Laurent, Laura Samaison, Blandine Boisselier, Matthieu Talagas, Sebastian Costa, Jacqueline Aziza, Karima Mokhtari, Cédric Le Maréchal, and Pascale Marcorelles.
• Inserm, U1078, Brest, F-29200 France; CHRU Brest, Service d'anatomie et cytologie pathologiques, Brest, F-29220 France; Université Européenne de Bretagne, 29238 France. Electronic address: arnaud.uguen@chu-brest.fr.
• Hum. Pathol. 2015 Aug 1; 46 (8): 1189-96.

AbstractDiffuse leptomeningeal melanocytosis (DLM) is a rare nevomelanocytic proliferation arising in the meninges. Despite their lack of morphological features of malignancy, these clonal nevomelanocytic cells are capable of extensive invasion and of malignant behavior. When associated with congenital melanocytic nevi, the disorder is named neurocutaneous melanocytosis (NCM). When symptomatic, DLM is usually revealed during childhood, but some cases remain clinically silent. The aim of this study was to analyze melanocytic proliferation in 2 rare and severe cases of isolated DLM and NCM of prenatal onset by neuropathologic and molecular analysis. We performed neuropathologic examination, comparative genomic hybridization arrays, fluorescence in situ hybridization, BRAF and NRAS pyrosequencing in the 2 cases, and next-generation sequencing in the case of isolated DLM. The neuropathologic examination showed diffuse meningeal melanocytic proliferation involving the whole central nervous system with multiple areas of intraneural invasion, associated with large nevi in 1 case. We did not find any chromosomal imbalances. A NRAS(Q61K) mutation was found in the cutaneous and meningeal lesions from the NCM. No mutation was found within a panel of oncogenes including BRAF, NRAS, HRAS, KIT, GNAQ, and GNA11 concerning the isolated DLM. We report 2 exceptional cases of hydrocephalus of prenatal onset related to DLM and NCM. The molecular mechanisms underlying our case of DLM remain unsolved despite the panel of analysis applied. Copyright © 2015 Elsevier Inc. All rights reserved.

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