V. Valayannopoulos

Posterior fossa imaging in 158 children with ataxia

OBJECTIFS To propose a MRI cerebellar algorithm that may be applied to guide genetic/malformative or biochemical investigations for patients with cerebellar ataxia. PATIENTS AND METHODS Cerebral MRI of 158 patients with cerebellar ataxia and no supratentorial abnormality were examined according to a new categorization system based on posterior fossa imaging. The clinical and radiological findings were confronted to biochemical and/or genetic results using the MR cerebellar algorithm. Seven groups of cerebellar MRI pattern were described: vermian dysgenesis (n=27), cerebellar hypoplasia (n=15), hemispheric cerebellar dysgenesis (n=6), unilateral hemispheric atrophy (n=5), global cerebellar atrophy (n=84), signal abnormalities (n=11) and normal MRI (n=10). Cerebellar hypoplasia, vermian dysgenesis and hemispheric cerebellar dysgenesis groups were classified as malformative disorders. Global atrophy and signal abnormality groups were classified as metabolic disorders. RESULTS In the vermian dysgenesis group, a specific genetic diagnosis was obtained in eight children (8/27) and all of the mutated genes (AHI1 (JBS3), CEP290 (JBS5), TMEM67 (JBS6), and RPGRIP1L (JBS7)) are involved in primary cilia function. In the group of pontocerebellar hypoplasia specific genetic diagnosis was obtained in one patient (PCH2) (1/15). Thus, nine of 42 children classified as malformative disorder had a molecular diagnosis. Global atrophy and signal abnormality groups were classified as metabolic disorders, specific biochemical was obtained in 46/95 children. In global atrophy group, respiratory chain deficiency was diagnosed in 18 children (18/84). In 21 children a congenital disorders of glycosylation type 1a (CDG Ia) was diagnosed (21/84) and infantile neuroaxonale dystrophy (INAD) was diagnosed in one child. In signal abnormalities group, specific biochemical diagnosis was obtained in six out of 11 children, five children with respiratory chain deficiency and one child with sulphite oxidase deficiency. In hemispheric cerebellar dysgenesis and normal MRI groups, no biological diagnosis was found for any of the patients. In the group of unilateral hemispheric atrophy, we hypothesized a clastic prenatal injury. CONCLUSION The proposed MR cerebellar algorithm was useful to guide genetic/malformative or biochemical investigations, allowing an etiological diagnosis in 55 children.

Mitochondrial ND5 mutations mimicking brainstem tectal glioma

We report MRI periaqueductal T2 hypersignal suggestive of tectal glioma in 3 unrelated children with reduced vision and normal mental development (figure). Increased CSF lactate and optic atrophy in the first case suggested …

SFP-P135 – Métabolisme – Réversibilité d’anomalies de signal à l’IRM après coma hyperammoniémique néonatal

Le cycle de l’uree permet l’excretion d’azote issu du metabolisme des acides amines par la conversion d’ammoniaque en uree dans le foie. Les deficits enzymatiques du cycle de l’uree (incidence cumulee : 1/8.000) se manifestent le plus souvent par une encephalopathie liee a la toxicite cerebrale de la glutamine au niveau des astrocytes. Le diagnostic precoce d’une hyperammoniemie neonatale avec mise en place de traitements epurateurs de l’azote (hemofiltration, chelateurs) peut permettre la survie de ces enfants. Une difficulte est alors l’evaluation des sequelles de cette decompensation. En dehors des criteres de gravite du coma et de l’EEG, l’IRM est mise a contribution. Il n’existe cependant que tres peu de documentations neuroradiologiques notamment en periode neonatale. Cas clinique Nous rapportons ici le cas clinique d’E.-G., nee a terme, qui a ete admise pour un tableau digestif en reanimation a J2, evoluant rapidement vers un coma. L’ammoniemie retrouvee elevee (max. 600 μmol/l) a pu etre corrigee en 48 h par hemofiltration et traitement medicamenteux. L’analyse des acides amines plasmatiques a permis le diagnostic de deficit en argininosuccinate synthetase (citrullinemie type I), confirmee par l’etude moleculaire. L’IRM a J13 montrait des anomalies en T1 et T2 des noyaux gris centraux avec hypersignal des noyaux lenticulaires predominant sur les regions pallidales associe a des anomalies de signal bilaterales symmetriques corticosouscorticales predominant en regions insulaires ayant fait evoquer la possibilite d’une necrose hemorragique. L’imagerie de controle realisee a 6 mois montrait cependant une quasi disparition de ces anomalies de signal. Le developpement psychomoteur de l’enfant a l’âge de 1 an est excellent. Conclusion Alors que l’aspect des lesions en phase precoce est assez specifique de l’atteinte neurologique par hyperammoniemie, il n’est pas forcement associe a un mauvais pronostic neurologique et peut regresser de facon quasi complete.