A brain lesion is an abnormality seen on a brain imaging test, such as an MRI or CT scan. 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.
A brain lesion usually is discovered during an imaging test for an unrelated condition or symptom. Concussions and lesions are not the same thing. Concussions more often occur without ever causing any changes on the CT or MRI images, and are diagnosed by symptoms and not imaging tests.