Internal borderzone infarction following acute middle cerebral artery occlusion.

In 36 patients suffering acute middle cerebral artery (MCA) occlusion, we studied the angiographic findings within 6 hours of the ictus and the chronic CT results at 3 months. Seven patients suffering distal pial MCA branch occlusion developed a pattern of internal borderzone infarction on follow-up CT. Carotid artery or carotid siphon stenosis or occlusion was absent in all seven. Proximal MCA branch occlusions, prior to the origin of the lenticulostriate arteries, were associated with extensive cortical and deep infarction in the entire MCA territory in 14 patients. There was proximal carotid artery or siphon stenosis or occlusion in 12 of these 14 patients. The remaining 15 patients showed a mixture of proximal and distal MCA occlusions and patchy ischemic damage in the MCA territory. There were no cases of superficial cortical watershed infarction. These data show that internal borderzone infarctions may result from intracranial MCA branch occlusions alone and need not be associated with hemodynamic alterations due to large vessel extracranial disease.