CLASSIFICATION OF DISORDERS OF BRAIN DEVELOPMENT
Development of the central nervous system occurs in several stages: dorsal induction (3-4 weeks’ gestation), ventral induction (3-4 weeks’ gestation), cell proliferation (10-18 weeks’ gestation), cell migration (3-5 months’ gestation), synaptic development (5 months’ gestation to postnatal), and myelination (postnatal). Depending on time of insult or error in programming, different disorders result (Table 8–1).
Table 8–1.Representative brain malformations. ||Download (.pdf) Table 8–1. Representative brain malformations.
Holoprosencephaly: alobar, semilobar, lobar, interhemispheric, septo-optic, holodiencephaly, microform
Agenesis of the corpus callosum, interhemispheric cysts, pericallosal lipoma
Septo-optic dysplasia, absent septum pellucidum
Meningomyelocele, myelocele, meningocele
Lumbosacral lipoma (lipoma, lipomeningocele)
Tight filum terminalus
Ventral dysraphism (sacral meningocele, neuroenterocyst, sacral agenesis)
Dermoid tumor, dermoid sinus
Cephalocele: meningocele, encephalocele
Malformations of cortical development
Malformations secondary to abnormal neuronal and glial proliferation or apoptosis (congenital microcephaly, megalencephaly, cortical dysgeneses with abnormal cell proliferation)
Malformations due to abnormal neuronal migration (periventricular nodular heterotopia, lissencephaly, subcortical heterotopia, cobblestone malformations)
Malformations secondary to abnormal postmigrational development (polymicrogyria, schizencephaly; focal cortical dysplasias type without dysmorphic neurons; postmigrational developmental microcephaly)
Molar tooth–associated malformations (Joubert syndrome)
With development of computed tomography scanning and, later, magnetic resonance imaging (MRI) scanning, brain imaging has become the mainstay for the diagnosis of brain malformations. Historically, brain malformations have presented in children with developmental delay, motor disorder, seizures, and abnormalities in head size. However, with improved resolution of prenatal ultrasound complemented by fetal MRI scan, brain malformations are increasingly being recognized in utero.
As one approaches brain images of children suspected of having a brain malformation, the following should be examined: midline structures (interhemispheric fissure, septum pellucidum, corpus callosum, hypothalamus, pituitary gland, and optic nerves; presence of any interhemispheric lipomas or cysts), cerebral cortex (cortical thickness, gyral pattern, and cortical gray-white matter junction), cerebral white matter (myelination, presence of any heterotopia or clefts), subcortical nuclei (any dysmorphism, midline fusion), ventricular system (segmentation of lateral ventricles, size and shape of ventricles, patency of cerebral aqueduct), and posterior fossa (brainstem, cerebellum, and craniocervical junction; presence of any cysts).1 Similarly, in approaching spinal cord images in a child with a suspected spinal cord malformation, one should examine the following: spinal cord (closure of neural tube, intramedullary structure, central canal), conus medullaris and cauda equina (filum terminalis, level of termination), vertebral arches, and overlying skin.
If a developmental brain abnormality is discovered, then further assessment of the underlying cause should be considered to determine the need for assessment of other organ systems, prognosis, and recurrence risk assessment. A 3-generation family pedigree should be obtained, ...