Proliferation, neuronal migration, and organization occur relatively late in pregnancy and do not end until after delivery.
Malformations of cortical development (MCD) may be diagnosed during fetal life; the chances for diagnosis are better in severe cases and in those with associated anomalies.
MCD assay may in same cases diagnosed by using ultrasound. Characteristic features are shown in Figure 7–1.
Even when MCD is suspected, a definitive diagnosis is usually difficult during pregnancy.
In patients at risk, search systematically for signs of MCD. Check for the size of the lateral ventricles and the regularity of their walls; also, the presence of abnormal underdeveloped or overdeveloped sulci.
When a suspicion is raised, consult with a genetician and a pediatric neurologist. In low-risk patients, these signs may be the only possibility for prenatal diagnosis.
Ultrasound signs of malformations of cortical development.
The processes of primary neurulation and ventral induction that result in the formation of the neural tube and in the formation of the prosencephalon, respectively, are completed by the second month of gestation.1 This is followed by three overlapping phases of cortical development, which are under the control of numerous genes: proliferation, migration, and organization. Stem cells at the surface of the ventricles proliferate and divide into glial cells and neuronal cells. The glial cells migrate to the cortex in a very regular radial pattern, leaving a radial scaffolding along which the neurons migrate (radial migration) to the surface. The later arriving neurons migrate in stages through the inner layers and ultimately lie outside them (inside out migration). Ultimately, six layers are formed. Once the neurons arrive at the cortex, they organize local connections. In addition to this radial migration, there is a tangential migration of neurons to form what are believed to be controlling tracts.2 The genes that control neuronal development also function in other parts of the body, so it is not unusual to find cerebral malformations associated with diverse somatic manifestations, such as skeletal dysplasia as present in thanatophoric dysplasia. This normal orderly developmental process can be disturbed by genetic, teratogenic, and environmental conditions. Because the cerebrum develops simultaneously with other structures, an insult at a specific time can affect the normal development of all the structures that are vulnerable at that time, including the eyes, face, and hindbrain. Hence the importance of assessing all of these areas if abnormality is suspected in any one of them. Over the past decade, the knowledge regarding the genetics, morphology, and clinical aspects of these conditions has expanded significantly, and new developments in this field have occurred rapidly.
Different classifications of malformations of cortical development (MCD) have been proposed3,4,5 (Table 7–1). Fundamentally, they are based on two factors: gene abnormality and timing of the first abnormal developmental event. ...