The mechanism of this type of massive brains swelling is not known but may have to do with disruption of endothelial barriers in the infarcted regions and the passive transit of water and solutes into brain tissue. Presumably the main factor in swelling is edema rather than increased blood volume. That the size of the infarct is more important in the than reperfusion of a region was shown by Kimberly et al, who analyzed patients in one of the larger endovascular thrombectomy trials and found that successful reperfusion was associated with less edema.
Intravenous mannitol in doses of 1 g/kg, then 50 g every 2 or 3 h, or hypertonic saline may forestall further deterioration, but most of these patients, once comatose, are likely to die unless drastic measures, such as hemicraniectomy, are taken. In such instances, controlled hyperventilation may be useful as a temporizing maneuver. Glucocorticoids are of little value; several trials have failed to demonstrate their efficacy.
In the past several decades, there has been the inception of hemicraniectomy as a means of reducing the mass effect and intracranial pressure in these extreme circumstances (see Schwab et al). One favored approach has been to perform hemicraniectomy early in the course of brain swelling, in the first 2 or 3 days, when the patient is drowsy but before coma supervenes. A pooled analysis of three randomized trials based on this premise has been given by Vahedi and colleagues. Excluding patients older than age 60 years, a total of 93 patients who were not fully alert could be analyzed. An advantage in survival was found favoring the group operated within 48 h. There has been controversy regarding the functional status of survivors and this involves the matter of the desirability of patients remaining with modified Rankin scale scores of 4, meaning they are dependent on others for their personal care. A controlled trial conducted in patients over age 60 has confirmed a beneficial effect of hemicraniectomy in preventing death from brain swelling after stroke. However, not surprisingly, the proportion of survivors with good functional outcomes in this older group was not as high as for younger patients.
One practice has been to wait for signs of deterioration, generally leading to operation on fewer than half of patients with large MCA territory strokes and, generally having operations from the third through fifth days. The family must understand the risks involved and the likelihood that the stroke deficits will persist so that approximately a third of surviving patients will be dependent for care. Hemicraniectomy combined with an overlying duraplasty is then undertaken if the patient is progressing from a stuporous state to coma and imaging studies show increasing mass effect. Whether anterior temporal lobectomy is of added benefit is not known, but it is now infrequently included. The value of surgical decompression has not been limited to patients with right-hemispheric strokes; those with mild or moderate of aphasia may also be appropriate candidates. After a protracted period of coma with bilaterally enlarged pupils or with evidence that the midbrain has been irrevocably damaged, the procedure may be futile.