A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.

Pachygyria is a malformation of cortical development with abnormally wide gyri with sulci 1,5-3 cm apart and abnormally thick cortex measuring more than 5 mm (radiological definition). See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly.

Spastic paralysis affecting all four limbs.

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Increased vertical dimension of the corpus callosum. This feature can be visualized by sagittal sections on magnetic resonance tomography imaging of the brain.

Subcortical band heterotopia is a condition in which nerve cells (neurons) do not move (migrate) to their proper locations in the fetal brain during early development. (Heterotopia means "out of place.") Normally, the neurons that make up the outer surface of the brain (cerebral cortex) are distributed in a well-organized and multi-layered way. In people with subcortical band heterotopia, some neurons that should be part of the cerebral cortex do not reach it. These neurons stop their migration process in areas of the brain where they are not supposed to be and form band-like clusters of tissue. Since these bands are located beneath the cerebral cortex, they are said to be subcortical. In most cases, the bands are symmetric, which means they occur in the same places on the right and left sides of the brain.\n\nThe abnormal brain development causes neurological problems in people with subcortical band heterotopia. The signs and symptoms of the condition depend on the size of the bands and the lack of development of the cerebral cortex. The signs and symptoms can vary from severe intellectual disability and seizures that begin early in life and affect both sides of the brain (generalized seizures) to normal intelligence with seizures occurring later in life and affecting only one side of the brain (focal seizures). Some affected individuals also have weak muscle tone (hypotonia), loss of fine motor skills such as using utensils, or behavioral problems. Subcortical band heterotopia is typically found when brain imaging is done following the onset of seizures, usually in adolescence or early adulthood.

A congenital abnormality of the cerebral hemisphere characterized by lack of gyrations (convolutions) of the cerebral cortex. Agyria is defined as cortical regions lacking gyration with sulci great than 3 cm apart and cerebral cortex thicker than 5 mm.

Infantile spasms represent a subset of "epileptic spasms". Infantile Spasms are epileptic spasms starting in the first year of life (infancy).

An abnormally thin corpus callous, due to atrophy, hypoplasia or agenesis. This term is intended to be used in situations where it is not known if thinning of the corpus callosum (for instance, as visualized by magnetic resonance tomography) is due to abnormal development (e.g. a leukodystrophy) or atrophy following normal development (e.g. neurodegeneration).

Head circumference below 2 standard deviations below the mean for age and gender.

A cataract is an opacity or clouding that develops in the crystalline lens of the eye or in its capsule.