Cerebral atrophy is a common feature of many of the diseases that affect the brain. Atrophy of any tissue means a decrement in the size of the cell, which can be due to progressive loss of cytoplasmic proteins. In brain tissue, atrophy describes a loss of neurons and the connections between them. Brain atrophy can be classified into two main categories: generalized and focal atrophy. Generalized atrophy occurs across the entire brain whereas focal atrophy affects cells in a specific location. If the cerebral hemispheres (the two lobes of the brain that form the cerebrum) are affected, conscious thought and voluntary processes may be impaired. Some degree of cerebral shrinkage occurs naturally with the dynamic process of aging. The human brain completes growth and attains its full maturity at 25 years of age. Structural changes continue during adulthood as brain shrinkage commences after the age of 35, at a rate of 0.2% per year. The rate of decline is accelerated when individuals reach 70 years old. By the age of 90, the human brain will have experienced a 15% loss of its initial peak weight. Besides brain atrophy, aging has also been associated with cerebral microbleeds. Symptoms
Many diseases that cause cerebral atrophy are associated with dementia, seizures, and a group of language disorders called the aphasias. Dementia is characterized by a progressive impairment of memory and intellectual function that is severe enough to interfere with social and work skills.
When looking at images of a brain with posterior cortical atrophy, one can see a loss in volume of the dorsal and ventral visual pathways, where visual stimuli is brought to the visual cortex and integrated information is sent back out to other areas of the brain. Because this disorder results in visual impairments, there is often a missed or delayed diagnosis, as the assumption is that there is a problem is in the eyes when the reality is that the problem is all the way in the back of the brain. Prion diseases, a group of invariably fatal encephalopathies that cause the progressive death of neurons. Infections
Where an infectious agent or the inflammatory reaction to it destroys neurons and their axons, these include...

Encephalitis, acute inflammation in the brain
Neurosyphilis, an infection in the brain or spinal chord
AIDS, disease of the immune system

Drug-induced
Alcohol (partially reversible): Standardized MRI evidence suggest chronic alcoholism (alcohol use disorder) is associated with widespread cortical atrophy and major brain changes. In contrast to healthy controls, macrostructural findings indicate alcoholic brains are smaller in mass and volume. Neuroimaging studies also show that cortical shrinkage in "uncomplicated alcoholism" is most severe in the frontal lobe in comparison to the other divisions of the cerebral cortex. In addition, neurological diseases that co-occur with excessive alcohol consumption—such as Wernicke-Korsakoff syndrome (WKS)—are characterized by substantial volume deficits of the diencephalon structures.