A brain lesion is an abnormality seen on a brain-imaging test, such as magnetic resonance imaging (MRI) or computerized tomography (CT). On CT or MRI scans, brain lesions appear as dark or light spots that don't look like normal brain tissue.

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.

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 or follow-up tests may be necessary.

Among the known possible causes of brain lesions are:

• Brain aneurysm
• Brain AVM (arteriovenous malformation)
• Brain tumor (both cancerous and noncancerous)
• Encephalitis (brain inflammation)
• Epilepsy
• Hydrocephalus
• Multiple sclerosis
• Stroke
• Traumatic brain injury

While brain trauma of any sort may result in a concussion as well as a brain lesion, concussions and brain lesions are not the same thing. Concussions more often occur without ever causing any changes on the CT or MRI and are diagnosed by symptoms rather than imaging tests.

If a brain lesion discovered during a brain-imaging test doesn't appear to be from a benign or resolved condition, your doctor will likely seek more information from additional testing or consulting a specialist.

Your doctor may recommend that you see a neurologist for a specialized examination and, possibly, further tests. Even if a neurological work-up doesn't result in a diagnosis, your doctor may recommend continued testing to reach a diagnosis or follow-up imaging tests at regular intervals to monitor the lesion.