The examination revealed extensive brain damage, including microcephaly, migration anomalies, callosal dysgenesis, and a massive neuroglial, leptomeningeal heterotopia covering the left hemisphere.In 1977, Dr. Clarren described a second infant whose mother was a binge drinker. The infant died ten days after birth. The autopsy showed severe hydrocephalus, abnormal neuronal migration, and a small corpus callosum (which connects the two brain hemispheres) and cerebellum. FAS has also been linked to brainstem and cerebellar changes, agenesis of the corpus callosum and anterior commissure, neuronal migration errors, absent olfactory bulbs, meningomyelocele, and porencephaly. Neurological
When structural impairments are not observable or do not exist, neurological impairments are assessed. In the context of FASD, neurological impairments are caused by prenatal alcohol exposure which causes general neurological damage to the central nervous system (CNS), the peripheral nervous system, or the autonomic nervous system. A determination of a neurological problem must be made by a trained physician, and must not be due to a postnatal insult, such as meningitis, concussion, traumatic brain injury, etc.All four diagnostic systems show virtual agreement on their criteria for CNS damage at the neurological level, and evidence of a CNS neurological impairment due to prenatal alcohol exposure will result in a diagnosis of FAS or pFAS, and functional impairments are highly likely.Neurological problems are expressed as either hard signs, or diagnosable disorders, such as epilepsy or other seizure disorders, or soft signs.
The four diagnostic systems list various CNS domains that can qualify for functional impairment that can determine an FASD diagnosis:

Evidence of a complex pattern of behavior or cognitive abnormalities inconsistent with developmental level in the following CNS domains – Sufficient for a pFAS or ARND diagnosis using IOM guidelinesLearning disabilities, academic achievement, impulse control, social perception, communication, abstraction, math skills, memory, attention, judgment
Performance at two or more standard deviations on standardized testing in three or more of the following CNS domains – Sufficient for an FAS, pFAS or static encephalopathy diagnosis using 4-Digit Diagnostic CodeExecutive functioning, memory, cognition, social/adaptive skills, academic achievement, language, motor skills, attention, activity level
General cognitive deficits (e.g., IQ) at or below the 3rd percentile on standardized testing – Sufficient for an FAS diagnosis using CDC guidelines
Performance at or below the 16th percentile on standardized testing in three or more of the following CNS domains – Sufficient for an FAS diagnosis using CDC guidelinesCognition, executive functioning, motor functioning, attention and hyperactive problems, social skills, sensory processing disorder, social communication, memory, difficulties responding to common parenting practices
Performance at two or more standard deviations on standardized testing in three or more of the following CNS domains – Sufficient for an FAS diagnosis using Canadian guidelines
Cognition, communication, academic achievement, memory, executive functioning, adaptive behavior, motor skills, social skills, social communication

Related signs
Other conditions may commonly co-occur with FAS, stemming from prenatal alcohol exposure. However, these conditions are considered alcohol-related birth defects and not diagnostic criteria for FAS.