Identification Of Patients For Hemicraniectomy

Early identification of patients susceptible to malignant MCA infarction is crucial. Neuroimaging is an invaluable tool for identifying patients at risk for developing ischemic brain edema. Neurologic deterioration correlates with horizontal displacement of the anterior septum and pineal gland (as seen on CT scan), rather than with ICP elevation. The presence of low-density infarction and edema that occupies more than 50% of MCA territory on CT scan is a reliable predictor of subsequent edema formation following a large hemispheric infarction. Early (<6 hr) CT scan changes of >50% MCA hypodensity or local brain swelling (effacement of sulci, compression of lateral ventricle) have been associated with fatal outcomes in 85% of patients (94% specificity and 61% sensitivity) (7). In addition, hemorrhagic transformation of large hemispheric infarctions might worsen the brain edema and tissue shifts. In a study of early radiologic signs on follow-up CT scan, the CT parameters anteroseptal shift >5 mm, pineal shift >2 mm, hydrocephalus, temporal lobe infarction, and presence of other vascular territory infarction predicted fatal outcomes (8). Case reports have also shown pineal shift of 2.5 to 4 mm from midline to be associated with drowsiness, 6 to 9 mm, with stupor, and >9 mm, with coma (9). In the European Cooperative Acute Stroke Study, fatal brain edema occurred in patients with baseline (<6 hr) CT scans that showed MCA involvement of greater than 33% (10) . Patients with baseline National Institute of Health Stroke Scale (NIHSS) >20 with left hemispheric infarctions, or >15 with right hemispheric infarctions, within six hours of symptom onset, accompanied by nausea/vomiting or >50% MCA territory hypodensity on CT scan have been shown to be at high risk for developing fatal brain edema (6 ). Single-photon emission computed tomography (SPECT), xenon CT, and cerebral angiography are also helpful in identifying site of occlusion, status of collateral blood supply, and level of residual blood flow. Marked activity deficits within the complete MCA territory on ultra-early SPECT scans have been found to be superior in predicting malignant MCA infarction than have CT scans or clinical predictors (Scandinavian Stroke Scale, level of consciousness, or gaze deviation) (11). Mean cerebral blood flow in the symptomatic MCA territory on xenon-CT has been found to be 8.6 mL/100 g/min in patients who developed brain herniation, compared with 18 mL/100 g/min in those who did not develop herniation. Mean cerebral blood flow in the symptomatic MCA territory of 15 mL/100 g/min in all patients was significantly associated with the development of severe edema and hernia-tion (12). Results of one study showed that terminal internal carotid artery (carotid-T) occlusion, demonstrated on angiography, is a better predictor than CT cortical hypodensity in one-third of patients with MCA (13). The absence of collateral supply, recanalization, and internal carotid artery occlusion were predictors of death in patients with malignant MCA in the original series by Hacke et al. (1). Based on the published literature, we propose a management algorithm for groups at high risk for herniation that might need hemicraniectomy (Fig. 1).

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