thanks for your query at HCM
Brain lesions are abnormal areas of tissue in your brain. On MRI
images, for example, brain lesions appear as dark or light spots that don't look like normal brain tissue.
If you've been diagnosed with something described as a brain lesion, it implies that the cause of the abnormal-appearing area cannot be diagnosed by the image alone, and further evaluation is necessary.
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.
causes for brain lesion:
Brain AVM (arteriovenous malformation
Traumatic brain injury
so brain lesion can be due to any of the above the cause, careful examination of the patient and detailed history may help to come to diagnosis
hope this will help