Ischemic Lesions in Acute and Subacute Perimesencephalic Subarachnoid Hemorrhage.

Perimesencephalic hemorrhage (PMH) is a subtype of nonaneurysmal subarachnoid hemorrhage (SAH). In patients with aneurysmal SAH, the occurrence of acute ischemic lesions is associated with severity and poor outcome. We investigated the frequency of ischemic lesions on DWI in patients with PMH and compared it with the frequency of ischemic lesions in patients with aneurysmal SAH. From a prospective cohort of 80 patients with acute spontaneous SAH, we included 15 patients with PMH and 39 patients with aneurysmal SAH who were matched on the basis of their clinical condition (World Federation of Neurological Societies grade 1 or 2). MRI was performed less than 72 hours after SAH, 8-10 days after SAH, or at both points in time. The number and distribution of lesions previously seen on DWI that were also seen on a second MRI examination were assessed. Nonparametric tests were used to compare groups. Early acute ischemic lesions (those identified < 72 hours after SAH) were found in 46.2% of patients with PMH and in 62.9% of patients with aneurysmal SAH. No significant differences in the number of acute ischemic lesions between groups were noted less than 72 hours after SAH (median, 0.5 lesion [interquartile range {IQR}, two lesions] in patients with PMH vs one lesion [IQR, three lesions] in patients with aneurysmal SAH [p = 0.48] or 8-10 days after SAH (median, 0.5 lesion [IQR, four lesions] in patients with PMH vs 1.5 lesions [IQR, three lesions] in patients with aneurysmal SAH [p = 0.26]). However, 58.3% of patients with aneurysmal SAH had new infarcts at 8-10 days, compared with 7.1% of patients with PMH. Patients with PMH had diffuse ischemic lesions, whereas patients with aneurysmal SAH in the anterior circulation had mainly supratentorial lesions. Early ischemic lesions appeared on DWI both in patients with PMH and in patients with aneurysmal SAH. The number of lesions increased during the time window for vasospasm, mainly in patients with aneurysmal SAH. Further studies are required to better understand the pathophysiologic mechanisms behind early ischemia in patients with PMH and their impact on prognosis.