Under normal circumstances, brain atrophy mostly occurs at the age of fifty or older, and the course of the disease can last for years or decades. If brain atrophy occurs when the patient is in his forties, the cause should be found from the patient’s lifestyle and underlying diseases. Brain atrophy is a phenomenon that occurs when the brain tissue itself shrinks for various reasons. A CT or MRI of the head can reveal a decrease in the size of the brain tissue and an enlargement of the ventricles. Brain atrophy is a manifestation of many diseases in imaging. Brain atrophy in patients in their forties may be caused by genetic factors, head trauma, or due to long-term seizures, cerebrovascular malformations, excessive smoking and drinking, poor nutrition, as well as gas poisoning, alcoholism, and thyroid dysfunction.