Isolated macrocerebellum: description of six cases and literature review.

BACKGROUND Macrocerebellum is a rare entity described as an isolated and abnormal increase of the cerebellum (CB) size without morphological or signal abnormalities. There have been only eleven patients with macrocerebellum reported in the literature so far. METHODS From December 2011 to March 2014, among 950 paediatric patients that underwent a magnetic resonance scan of the brain in our department, in six subjects an abnormal increase of the cerebellar volume was suspected. A volumetric analysis was performed in all patients on T1- weighted 3D imaging to confirm the diagnosis of macrocerebellum. The ratios between (I) volume of the CB and volume of the supratentorial structures (STB) and (II) volume of the CB and the sum of CB and STB (WB) were calculated in order to normalize the absolute values obtained and compared with the normal values present in literature. RESULTS AND DISCUSSION Quantitative analysis confirmed an increased cerebellar volume relatively to the STB volume ("t": 6.9518; P<0.001) and to the WB ("t": 7.1415; P<0.001) volume in comparison to the normal controls available in literature. Clinical characteristics and other neuroradiological findings of the patients are described. We also describe the differential features between isolated macrocerebellum and other pathological conditions that are characterized by cerebellar enlargement such as Lhermitte-Duclos, Sotos syndrome, Costello syndrome, Williams syndrome, Alexander disease and fucosidosis. Furthermore a detailed literature review is provided. Macrocerebellum is always associated with an abnormal mental and motor development. CONCLUSION Macrocerebellum is a neuroradiological entity that can be identified qualitatively and confirmed quantitatively through volumetric analysis. This is the largest cohort of patients with macrocerebellum described so far. The data available in literature on this entity show that macrocerebellum is not a specific disease but an epiphenomenon found in heterogeneous brain disorders.

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