Language disorders: clinical classification and neurovascular substrate.

The most prevalent cause of focal brain disease is stroke, Neuroanatomic localization in aphasia--and by inference, the identification of brain regions associated with language functions--is largely determined by, and confounded with, left cerebral hemisphere vascular territories. Traditional nosology of the aphasias, alexias, and agraphias is not always logically coherent and ignores major neurolinguistic boundries, yet it retains the clinical utility of permitting reliable and valid anatomic inferences concerning the underlying neuropathologic substrate.