A brain lesion is an abnormality seen on a brain-imaging test, such as magnetic resonance imaging (MRI) or a computerized tomography (CT) scan. 
Causes. Often, a brain lesion has a characteristic appearance that will help your doctor determine its cause. Sometimes the cause of the abnormal-appearing area cannot be diagnosed by the image alone, and additional tests or follow-up tests may be necessary. Among the known possible causes of brain lesions are: 1  Brain aneurysm. 1 Brain lesions (lesions on the brain) refers to any type of abnormal tissue in or on brain tissue. 2  Major types of brain lesions are traumatic, infectious, malignant, benign, vascular, genetic, immune, plaques, brain cell death or malfunction, and ionizing radiation. A lesion is an area of tissue that has been damaged through injury or disease. So a brain lesion is an area of injury or disease within the brain. While the definition sounds simple, understanding brain lesions can be complicated. That's because there are many types of brain lesions. Usually, a brain lesion is an incidental finding unrelated to the condition or symptom that led to the imaging test in the first place. A brain lesion may involve small to large areas of your brain, and the severity of the underlying condition may range from relatively minor to life-threatening. 1  Causes. MRI showing a brain lesion. A brain lesion is an abnormality seen on a brain-imaging test, such as magnetic resonance imaging (MRI) or a computerized tomography (CT) scan. On CT or MRI scans, brain lesions appear as dark or light spots that don't look like normal brain tissue. Brain lesions: Causes, symptoms, treatments. A brain lesion is an area of tissue that has been damaged by injury, infection, exposure to certain chemicals or problems with the immune system, and more. In some cases the cause is not known.
http://www.mayoclinic.org/symptoms/brain-lesions/basics/causes/SYM-20050692 http://www.emedicinehealth.com/brain_lesions_lesions_on_the_brain/article_em.htm http://www.webmd.com/brain/brain-lesions-causes-symptoms-treatments http://www.mayoclinic.org/symptoms/brain-lesions/basics/definition/SYM-20050692 http://www.mayoclinic.org/symptoms/brain-lesions/basics/definition/SYM-20050692 http://www.webmd.boots.com/a-to-z-guides/brain-lesions-causes-symptoms-treatments
what is a brain lesion