How often is a perimesencephalic subarachnoid haemorrhage CT pattern caused by ruptured aneurysms?
BACKGROUND
Angiography is usually recommended in perimesencephalic subarachnoid haemorrhage (PM SAH) to rule out a basilar artery aneurysm. However it is not known how often aneurysms are found among patients with a CT pattern of PM haemorrhage or the frequency of this CT pattern after rupture of posterior circulation aneurysms.


METHODS
CTs of all SAH caused by posterior circulation aneurysms admitted from 1/85 to 12/92 where reviewed by two examiners. Late (> 72h) examinations were excluded. The remaining CTs were classified in perimesencephalic (PM) or non PM.


RESULTS
81 posterior circulation aneurysms were collected. Only one PM-like CT pattern was found, due to ruptured posterior communicating artery aneurysm (1.3%; 95% Cl (confidence intervals) = .03-6.7%). During the same period 37 PM SAH with negative angiographic results were admitted. The likelihood of finding an aneurysm in a patient with an early CT showing a PM distribution of haematic densities was 2.7% (95% Cl = .07-.14%).


CONCLUSIONS
Although the probability of finding an aneurysm in a SAH patient with a PM CT pattern is low, a complete 4-vessel angiogram must be obtained.
Pinto
A N
AN
Department of Neurology, Hospital St. Maria, Lisbon, Portugal.
Ferro
J M
JM
Canhão
P
P
Campos
J
J
D017542:Aneurysm, Ruptured / Q000000981:diagnostic imaging* / Q000601:surgery; D002533:Cerebral Angiography; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000601:surgery; D008636:Mesencephalon / Q000000981:diagnostic imaging* / Q000601:surgery; D008875:Middle Aged; D009460:Neurologic Examination; D011183:Postoperative Complications / Q000000981:diagnostic imaging; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed