Injury
Stroke, loss of brain function due to a sudden interruption of blood supply in the brain
Moderate-to-severe traumatic brain injury

Diseases and disorders
Alzheimers disease (High resolution MRI scans have shown the progression of cerebral atrophy in Alzheimers disease)
Cerebral palsy, in which lesions (damaged areas) may impair motor coordination
Senile dementia, fronto-temporal dementia, and vascular dementia
Picks disease, causes progressive destruction of nerve cells in the brain
Huntingtons disease, and other genetic disorders that cause build-up of toxic levels of proteins in neurons
Leukodystrophies, such as Krabbe disease, which destroy the myelin sheath that protects axons
Multiple sclerosis, which causes inflammation, myelin damage, and lesions in cerebral tissue
Epilepsy, in which lesions cause abnormal electrochemical discharges that result in seizures
Anorexia nervosa, bulimia nervosa, and other eating disorders
Malnutrition, caused by lack or excess of nutrition from foods
Type II diabetes, where the body does not use insulin properly resulting in high blood sugar
Bipolar disorder, significant loss of brain tissue during manic episodes; however its not verified whether the episodes cause brain tissue loss or vice versa
Schizophrenia
Mitochondrial encephalomyopathies, such as Kearns–Sayre syndrome, which interfere with the basic functions of neurons
Posterior cortical atrophy:  In the most posterior area of the brain lies the visual cortex, the area of the brain where visual information is received and processed. When cortical atrophy occurs in this brain area due to neurodegeneration, the first symptom is impairment in vision. A common vision impairment seen in patients with posterior cortical atrophy is simultanagnosia, where a person is unable to see multiple locations at once or to quickly shift attention between these locations.
With both measures, multiple images can be compared to see if there is a loss in brain volume over time. Difference from hydrocephalus
Cerebral atrophy can be hard to distinguish from hydrocephalus because both cerebral atrophy and hydrocephalus involve an increase in cerebrospinal fluid (CSF) volume. In cerebral atrophy, this increase in CSF volume comes as a result of the decrease in cortical volume. In hydrocephalus, the increase in volume happens due to the CSF itself. Treatment
Cerebral atrophy is not usually preventable. However, there are steps that can be taken to reduce the risk:

controlling blood pressure
a healthy balanced diet including omega-3s and antioxidants
staying active mentally, physically, and socially. Reversibility of cerebral atrophy
While most cerebral atrophy is said to be irreversible, recent studies that show this is not always the case. A child who was treated with ACTH originally showed atrophy, but four months after treatment the brain was seemingly normal again.As previously mentioned, chronic alcoholism is known to be associated with significant brain damage. The pronounced shrinkage in the frontal lobes and cerebellum of alcoholics correlates with serious impairments in executive and psychomotor functions. However, longitudinal studies suggest that some of these brain damages are partially reversible with abstinence. In response to drinking cessation, bodies of gray and white matter including the cerebral cortex, the limbic system (amygdala, hippocampus, thalamus), the cerebellum, and the brainstem all showed a general increase in brain volume. Similarly, ventricular enlargement—which reflects atrophy of surrounding brain regions—is also reduced in abstinent alcoholics.