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Neuropsychologists frequently work with patients who have specified brain lesions that produce well-documented cognitive or behavioral effects. However, for those clinicians working with school-age children or adolescents who suffer developmental disorders, the pathogenesis of cognitive and behavioral deficits may be poorly understood. It should be noted, however, that considerably more is now known about neurological anomalies than in decades past. Consequently, it is more widely recognized that knowledge of neurodevelopmental processes should underscore clinical practice (Riccio & Pizzitola-Jarratt, 2005). This chapter reviews the anomalies of neurological development that not infrequently are seen in children and adolescents with developmental disorders. Most typically the neuropsychological manifestations of these anomalies impact on widely distributed functional systems, thus producing generalized and severe impairment. However, there are exceptions, especially with regard to anomalies of neuronal migration. Some basic understanding of these effects should aid neuropsychologists in a better conceptualization of how disorders of neurological development produce different effects than do discrete lesions of the central nervous system. There is wide variability in neuroanatomical development and, unfortunately, there is still incomplete understanding of neurodevelopmental anomalies. Our ability to define these anomalies by pathogenesis or prognosis is greater than our ability to relate them to functional or behavioral deficits. However, it is increasingly clear that a better understanding of the brain enhances the appreciation as to relations between brain functioning and the processes and behaviors we typically assess (Reynolds & French, 2005). Essentially three categories of anomalies can be specified: (1) those incompatible with life, (2) those not necessarily incompatible with life but that severely impair functioning, and (3) those of variable consequences such that they can be asymptomatic or associated with subtle cognitive and behavioral deficits. In this chapter, five general types of neurodevelopmental anomalies, as defined by pathogenesis, will be addressed: (1) bulk brain growth abnormalities, (2) cerebral hemisphere dysplasias, (3) cerebral cortex malformations, (4) hydrocephalus and associated anomalies, and (5) neural tube abnormalities and fusion deficits. |
