Pigmented (melanin producing) desmoplastic ganglioglioma
This tumor disclosed all the classic microscopic features of a desmoplastic infantile ganglioglioma except the perivascular inflammatory infiltrate, which is much more common in pure gangliogliomas, and the pigment deposits which were shown to be melanin. Pigmented primary intracranial tumors other than meningeal melanocytomas and melanomas are rare. However, some pigmented neoplasms in the central nervous system (CNS), either neuroepithelial or non-neuroepithelial ones, have been reported (4, 5, 8)
The nature of these pigments has been shown to be either melanin, which derives from melanosomal activity, or neuromelanin, which results from catecholamine synthesis (2, 5); in some cases, lipofuscin, a pigment that is derived from oxidation of lipids or lipoprotein sources, has been shown in addition to neuromelanin. Melanosomal melanin and neuromelanin have distinctive ultrastructural features. Some authors suggested that neuromelanin is a melanized form of lipofuscin, because of their histochemical similarities (2). Pigments are normally found in certain parts of the CNS: melanin in meninges, fetal pineal gland and pigmented layer of retina; neuromelanin in substantia nigra and locus ceruleus; lipofuscin in precentral gyrus, nuclei of cranial nerves, red nucleus, part of thalamus, globus pallidus, inferior olives and dentate nucleus (2).
There are only three previous reports of pigmented ganglioglioma: one case of a melanotic ganglioglioma of the pineal region (4), another of a ganglioglioma of the temporal lobe with evidence of melanogenesis in neoplastic astrocytes (8), and, finally, a desmoplastic infantile ganglioglioma (1). This report addressed a 9-month-old boy with a temporo-mesial mass, and in which the ultrastructural exam disclosed cells with melanosomes and premelanosomes. This enlarges the evidence that melanin production is not restricted to cells of neuronal crest derivation and that central neuroepithelial cells are also capable of melanogenesis (4, 5, 8).
The differential diagnoses to consider in this case are: the pleomorphic xanthoastrocytoma, with two pigmented cases reported previously (3, 7), the ganglioglioma, the desmoplastic infantile astrocytoma (9) and the desmoplastic infantile ganglioglioma. The first two are typically encountered in childhood, with involvement of the subarachnoid space and a history of seizures but, despite the coexistence of some similar microscopic features, these diagnoses were excluded by presence of ganglion cells. The diagnosis of desmoplastic ganglioglioma was made instead of ganglioglioma because of the prominent desmoplastic reticulin-rich stroma. The case reported has also the peculiar feature of being a desmoplastic non-infantile ganglioglioma. Indeed, desmoplastic gangliogliomas are uncommon supratentorial brain tumors typically occurring in children below the age of 24 months, usually with good prognosis. Only 20 cases of non-infantile desmoplastic gangliogliomas have been reported in the literature, none of them pigmented (6).
Contributed by Sónia Costa; Joana Marques; Pedro Pereira; Carla Firmo; José Pimentel