• aneurysmal subarachnoid hemorrhage;
  • cerebral blood flow;
  • computed tomographic perfusion;
  • perimesencephalic hemorrhage


The cause of perimesencephalic hemorrhage is unknown, but a venous source is suggested. If perimesencephalic hemorrhage is of venous origin, less elevation of the intracranial pressure and less perfusion deficits are expected than after aneurysmal subarachnoid hemorrhage.


We compared perfusion in the acute stage after perimesencephalic hemorrhage and aneurysmal subarachnoid hemorrhage.


We included 45 perimesencephalic hemorrhage patients and 45 aneurysmal subarachnoid hemorrhage patients, who were matched on clinical condition at admission and underwent computerized tomographic scanning <72 h after subarachnoid hemorrhage. Cerebral blood flow was assessed in 12 predefined regions of interest. Differences in cerebral blood flow values with corresponding 95% confidence intervals were calculated. Sub-group analyses were performed stratified on comparable amounts of blood and location of blood (posterior circulation aneurysms and additionally in infratentorial and supratentorial aneurysms).


Cerebral blood flow was higher in perimesencephalic hemorrhage patients (mean: 63·8) than in aneurysmal sub-arachnoid hemorrhage patients (mean: 55·9; difference of means: −7·9 [95% confidence interval: −10·7 to −5·2]) and also in the sub-group with comparable amounts of blood (mean cerebral blood flow: 56·4; difference of means: −7·4 [95% confidence interval: −10·4 to −4·3]). Cerebral blood flow was comparable with perimesencephalic hemorrhage patients for the sub-group with posterior circulation aneurysms (difference of means: −0·7 [95% confidence interval: −5·2 to 3·8]); however, differences diverged after stratifying posterior circulation aneurysms into supratentorial (difference of means −3·9 [95% confidence interval: −9·3 to 1·4]) and infratentorial aneurysms (difference of means 3·0 [95% confidence interval: −2·8 to 8·8]).


Perimesencephalic hemorrhage patients have a higher cerebral blood flow than aneurysmal subarachnoid hemorrhage patients. The findings of this study further support a venous origin of bleeding in perimesencephalic hemorrhage patients. Future studies should further elaborate on cerebral blood flow in posterior circulation aneurysms.