Malignant MCA Infarction: Pathophysiology and Imaging for Early Diagnosis and Management Decisions

Malignant middle cerebral artery infarction is a devastating condition, with up to 80% mortality in conservatively treated patients. The pathophysiology of this stroke is characterized by a large core of severe ischemia and only a relatively small rim of penumbra. Due to the fast development of irreversible morphological damage, cytotoxic edema occurs immediately in a large portion of the ischemic territory. The subsequent damage of the tight junctions leads to the breakdown of the blood brain barrier and vasogenic brain edema, resulting in space-occupying brain swelling. The progressive vasogenic edema reaches its maximum after 1 to several days and exerts a mechanical force on surrounding tissue structures leading to midline shift and transtentorial herniation and finally brain stem compression and death.Early severe neurological symptoms--hemiparesis, gaze deviation, higher cortical signs--followed by headache, vomiting, papillo edema and reduced consciousness may predict the deleterious course. Imaging supports the suspected diagnosis with hypodense changes on CT extending beyond 50% of the MCA territory. The size of the probably infarcted tissue and a midline shift on CT as well as the size of the lesion on diffusion-weighted MRI are predictive of a malignant course. Reduction of cerebral blood flow below a critical value and volume of irreversible tissue damage detected by positron emission tomography in the early hours after the stroke are indicative of progression to malignant infarction with increased intracranial pressure (ICP) and decreased tissue oxygen tension observed by multimodal neuromonitoring in the later course. Treatment options of malignant infarction include general measures to limit the extent of space-occupying edema, but these therapies have not been efficacious. Only surgical intervention with decompressive hemicraniectomy (DHC) was successful in relieving the effects of increased ICP and of the deleterious shifts of brain tissue. Several controlled clinical trials have proven the efficacy of DHC with a significant decrease in mortality and improved functional outcome. However, DHC must be performed early and with a large diameter, regardless of the age of patients, but in patients beyond 60 years, the higher likelihood of resulting severe disability should be taken into consideration.Malignant MCA infarction can be predicted early with a high sensitivity by neuroimaging. The early diagnosis is mandatory for DHC, which was shown to reduce mortality and improve functional outcome in several controlled clinical trials.