Brain lesions appear as dark or light areas that are distinctly different from the appearance of normal brain tissue on MRI scans, according to Mayo Clinic. A brain lesion may cover a large or insignificant area, and the seriousness of the underlying condition can vary widely.
Usually, the doctor detects the brain lesion by chance, and it is unrelated to the condition for which the doctor ordered the MRI, asserts Mayo Clinic. The doctor may also be able to define the underlying cause of the lesion by its appearance, but at times the doctor cannot determine the cause by the image from the MRI alone, and the patient must undergo further testing. Some common causes of brain lesions that show up on MRI scans include brain aneurysms, congenital brain abnormalities, cancerous and non-cancerous lesions, multiple sclerosis and traumatic injuries to the brain. Traumatic injuries may result in a concussion and a lesion, but the two are not the same thing, and most concussions do not result in brain lesions.
Doctors also use MRI scans as one of the most effective tools in diagnosing most types of brain tumors, reports the John Hopkins School of Medicine. MRI scans show images of the brain in slices that doctors can use to create a map of the tumor and determine its size and shape.