Melanosis of the dentate nucleus is an extremely rare condition in which pigment is formed within the cytoplasm and cytoplasmic processes of astrocytes in the dentate nucleus and the cerebellar granular cell layer. The pigment occurs as irregular polygonal structures of rather homogeneous appearance unlike granular neuromelanin located within neurons of the substantia nigra. The diameter of these pigment masses may reach 30 Μm or more. Their absorption of visible light increases steadily towards the shorter wavelengths, and the material is virtually opaque in the violet and ultraviolet region, resembling melanin in this respect. Since the absorption spectrum described by Rabl exhibited a small peak at 525 nm, he regarded the pigment as the hemoglobin derivative pentdyopent. We were unable, however, to confirm this observation. On X-ray diffraction the pigment produced a sharp reflex at 4.93 å as did synthetic melanin prepared from dopamine (but not melanin prepared from serotonin). These observations supported the assumption made by others based on histochemical evidence, that the pigment in the dentate nucleus may belong to the group of melanins. Presumably the glial melanin somehow arises from the metabolic pathway leading to DOPA. An astrocytic site of melanin formation other than in the cerebellum has not been previously described, and this melanin differs in appearance from the granular neuromelanin found in neurons in the substantia nigra. Thus “cerebellar glial melanin” contrasts with neuromelanin of the substantia nigra both in its site of formation and in its morphology.
The underlying cause of the glial melanin formation in the cerebellum is not known. There are six cases in the world literature, 5 females and 1 male, ranging in age from 58 to 103 years.
Involutional alterations in metabolism related to endocrine factors may possibly play an important part. To the best of our knowledge cerebellar melanosis is of no clinical relevance.
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Ule, G., Berlet, H., Haag, D. et al. Ein bisher kaum bekanntes gliogenes Melanin des Gehirns („Cerebellares Gliamelanin“). Virchows Arch. A Path. Anat. and Histol. 380, 335–339 (1978). https://doi.org/10.1007/BF00431318
- Glial Melanin
- Melanosis of the dentate nucleus
- Melanosis cerebelli