Early detection focal cortical gyration anomalies : prenatal MRI

Objectives: To highlight the magnetic resonance imaging (MRI)patterns of focal cortical gyration anomalies, as they appear at a very early stage of the sulcation process. Methods: We reviewed 950 fetal MRI studies performed at our institution between 2000 and 2006. The cases showing focal anomalies of the cortical rim before the 25th week of gestation were selected and classified according to the type of cortical ribbon distortion. Results: Among nine selected cases, we identified three basic patterns of cortical rim anomaly: ‘wart-like’, ‘saw-tooth’ and major aberrant invaginating sulci. All anomalies were already detectable when the brain was still smooth (‘physiological lyssencephaly’). The ‘wart-like’ and ‘saw-tooth’ patterns were confirmed to be focal polymicrogyria at follow-up. In one ‘wart-like’ case and in aberrant sulci cases the anomaly became more complex along with the gyration process. All cases were associated with additional brain anomalies: callosal partial agenesis, septum pellucidum agenesis, periventricular nodular heterotopias, focal thinning of migrating glia band and germinal matrix–ganglionic eminence hypertrophy. Five cases probably had a genetic basis, while the others were very probably of clastic origin. Conclusions: The present cohort shows how focal cortical gyration anomalies can be detected even at a very early stage of the sulcation process. Moreover, it shows how polymicrogyria and aberrant sulci grow along with normal brain maturation. The detection of migrating cell focal alterations suggests a migratory defect playing a role in the genesis of some focal gyration anomalies.