title: Unexplained mental retardation: is brain MRI useful?
abstract: 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.
  
  
  METHODS
  The MRI features and clinical data of 100 patients (age 1-18 years) 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.
authors.affiliation: Department of Radiology, Saint Vincent de Paul Hospital, 82 Avenue Denfert Rochereau, 75674 Paris Cedex 14, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Decobert
authors.forename: Sophie
authors.initials: S
authors.lastname: Grabar
authors.forename: Valerie
authors.initials: V
authors.lastname: Merzoug
authors.forename: Gabriel
authors.initials: G
authors.lastname: Kalifa
authors.forename: Gérard
authors.initials: G
authors.lastname: Ponsot
authors.forename: Catherine
authors.initials: C
authors.lastname: Adamsbaum
authors.forename: Vincent
authors.initials: V
authors.lastname: des Portes
mesh_terms: D000293:Adolescent; D001921:Brain / Q000002:abnormalities*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008607:Intellectual Disability / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018709:Statistics, Nonparametric
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