Diffuse leptomeningeal melanocytoma. The tumor was negative for BRAF mutation.
Leptomeningeal melanocytoma is a rare diagnosis. It is part of the primary melanocytic lesions of the CNS. These are defined as diffuse or circumscribed benign or malignant tumors arising from melanocytes of the leptomeninges (4). Clinical symptoms vary due to the different sites of appearance of the lesions. In our case the initial presentation with headache and dizziness could retrospectively be related to the diffuse meningeal affection. Neuroimaging was helpful for differential diagnosis (10) even though in most of the cases melanocytoma present with a mass lesion. The MRI could as well be interpreted as meningeal carcinomatosis. Morphologically, the tumor showed the typical appearance of a low-grade melanocytoma with epithelioid or spindle-shaped cells arranged in nests lacking anaplastic features. Furthermore, immunohistochemistry was positive for Melan-A, S100 and HMB45 (2). The low Ki67 labeling could explain the slow course of symptom progression and therefore late establishment of the diagnosis (8) even though low Ki67 is typical for melanocytomas. Lately two reports showed that melanotic nervous system tumors have several distinct mutational and chromosomal features which might allow a reliable differentiation. BRAF and KRAS mutations are very rare in melanocytomas compared to metastatic lesions (5, 6). On the other hand hotspot mutations in GNAQ or GNA11 are seen in the vast majority of melanocytomas which highlights a familiarity to uveal melanoma (9) This again could be helpful in establishing a diagnosis and be the basis for the development of targeted therapies. So far there is only unspecific, symptomatic therapy available due to the small number of cases (1, 3, 7). The patient received further treatment in form of whole brain radiation. Clinical symptoms as headache and signs of raised intracranial pressure during the following weeks lead to the diagnosis hydrocephalus malresorptivus (non-obstructive hydrocephalus) which was confirmed by a CT scan. Therefore a ventriculoperitoneal shunt for symptomatic therapy was implanted. The patient recovered slowly and was later transferred to rehabilitation.
Contributed by Lasse Dührsen, MD; Jakob Matschke, MD and Manfred Westphal, MD