Valérie Merzoug

MRI of the fetal posterior fossa.

MRI is a useful tool to complement US for imaging of the fetal posterior fossa (PF). In France, the discovery of a PF malformation in the fetus frequently leads to termination of pregnancy (80% in a personal series). However, despite improved accuracy in the diagnosis of PF abnormalities, prognosis remains uncertain. The first objective of this review is to document the normal MRI landmarks of the developing fetal PF. Because of their thinness, the visibility of the cerebellar fissures is dramatically delayed on MRI compared to macroscopic data. An important landmark is identification of the primary fissure of the vermis, normally seen at around 25–26xa0weeks’ gestation (WG) on the sagittal slice, separating the larger posterior lobe from the anterior lobe (volume ratio around 2:1). The prepyramidal and secondary fissures are usually only identifiable after 32xa0WG and the hemispheric fissures are difficult to see until the end of pregnancy. Considering the signal changes, high signal on T2-weighted (T2-W) sequences is seen from 25xa0WG in the posterior part of the brain stem (tegmentum and ascending sensory tracts) related to myelination. The low signal intensities seen within the cerebellum on T2-W images correspond to high cellularity of grey matter (deep nuclei), as there is no myelination within the white matter before 38xa0WG. The second objective is to highlight the signs highly predictive of a poor neurological prognosis. Lack of pontine curvature or vermian agenesis without a PF cyst (small volume of PF) is greatly associated with poor neurological status. The third objective is to propose a diagnostic strategy in difficult cases where prognosis is important, e.g. the Dandy Walker continuum. Analysis of the cerebellum is often impossible if a PF cyst is present (whatever its nature) as the mass effect usually blurs the foliation and even impairs evaluation of the normal ratio between the posterior and anterior lobes of the vermis. Isolated cerebellar hypoplasias raise the question of prognosis and genetic counselling. Such uncertainties require an amniocentesis and a careful search for other anomalies (cerebral and extracerebral). Unilateral abnormalities of a cerebellar hemisphere can be associated with good neurological status if they are isolated. The final objective is to discuss other rare PF fetal abnormalities, such as vascular malformations and tumours.

Unexplained mental retardation: is brain MRI useful?

Background: Mental retardation (MR), defined as an IQ below 70, is a frequent cause of consultation in paediatrics. Objective: To evaluate the yield of brain MRI in the diagnostic work-up of unexplained MR in children. Patients and methods: The MRI features and clinical data of 100 patients (age 1–18xa0years) affected with non-progressive MR of unknown origin were compared to an age-matched control group (n=100). Two radiologists conducted an independent review of the MRI scans. Results: Univariate and multivariate analyses showed a higher incidence of brain anomalies in the MR group than in the control group (53 vs 17, OR=5.7 [2.9–11.1]), for signal abnormalities within the periventricular white matter (OR=20.3 [2.6–155.3]), lateral ventricular dilatation (OR=15.6 [2.0–124]), mild corpus callosum abnormalities (shortness, atrophy) (OR=6.8 [1.8–25.6]) and subtle cerebellar abnormalities, including fissure enlargement (OR=5.2 [1.1–26.2]). The diagnostic value of MRI abnormalities was considered good in 5% of patients (Alexander disease n=1, diffuse cortical malformation n=1, leukomalacia n=1, vermian agenesis n=1, commissural agenesis n=1), and weak in 48% of patients, in whom non-specific abnormalities did not lead to a diagnosis. Some clinical features resulted in a significantly higher percentage of abnormal MRI scans: abnormal neurological examination (82% vs 47%, P=0.008), abnormal skull circumference (66% vs 49%, P=0.04). Motor delay was associated with cerebellar abnormalities (P=0.01). Conclusions: This study confirms the weak diagnostic yield of MRI in mentally retarded children. The use of a control group has enabled us to identify the neuroimaging markers frequently associated with MR. Subgrouping patients according to neuroimaging markers and clinical signs should help identify those who would benefit from molecular studies.

Bilateral dysplasia epiphysealis hemimelica: report of two cases

Dysplasia epiphysealis hemimelica is a rare congenital disorder characterised by unilateral bone overgrowth from large joints, mainly the ankle or knee. We present two cases with bilateral lesions; only two similar cases with bilateral involvement have been reported hitherto. The differential diagnosis is considered.

Imagerie cérébrale de la sclérose tubéreuse de bourneville chez l’enfant

Resume La sclerose tubereuse de Bourneville (STB) est une phacomatose frequente, de transmission autosomique dominante. Le diagnostic repose sur une liste de criteres (2 criteres majeurs ou 1 critere majeur + 2 criteres mineurs). L’IRM cerebrale est fondamentale au diagnostic en montrant les signes majeurs des la periode fœtale : nodules sous ependymaires, tubers et tumeurs a cellules geantes. Chez le grand enfant, les sequences FLAIR sont les plus performantes alors que chez le fœtus, le nouveau ne et le nourrisson, les sequences en T1 sont les plus contributives, du fait du processus de myelinisation.

Anomalies cérébrales subtiles de l'Adrénomyéloneuropathie

Purpose nTo describe subtle brain abnormalities detected on MRI in adult patients with adrenomyeloneuropathy (AMN).Resume Objectifs Decrire des anomalies cerebrales subtiles visibles en IRM chez des patients adultes atteints d’adrenomyeloneuropathie (AMN). Materiels et methodes Etude retrospective de donnees acquises prospectivement dans le cadre d’un essai therapeutique (Riluzole) de 66 adultes atteints d’AMN sans lesion cerebrale patente en IRM. Chaque patient a eu une IRM cerebrale a l’inclusion (T1, T2 et FLAIR, spectroscopie). Apres validation prealable d’une grille par 3 lecteurs differents, la lecture des IRM a ete effectuee consensuellement selon une echelle semi-quantitative. Resultats L’analyse preliminaire a confirme les anomalies de signal des faisceaux cortico-spinaux chez 36 patients (54,6 %). D’autres anomalies « subtiles » ont ete mises en evidence : aspect « delave » de la SB a predominance parieto-occipitale avec hypersignal modere, en plage chez 36 patients (54,6 %), hypersignal des fibres ponto-cerebelleuses en T2 et FLAIR chez 25 patients (41,7 %). L’augmentation des rapports Cho/Cr et mI/Cr decrite dans la litterature a ete confirmee. Conclusion Cette etude retrospective permet la description d’un « profil AMN » en IRM chez des patients ne presentant pas d’anomalie de la substance blanche et du corps calleux.