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Perimesencephalic nonaneurysmal subarachnoid hemorrhage

Farhan Siddiq, MD
Amir S Khan, MD
Section Editor
Jose Biller, MD, FACP, FAAN, FAHA
Deputy Editor
Janet L Wilterdink, MD


Subarachnoid hemorrhage (SAH) refers to bleeding within the subarachnoid space, which lies between the arachnoid and pia mater and is normally filled with cerebrospinal fluid. Most cases of subarachnoid hemorrhage are caused by rupture of an intracranial aneurysm, but approximately 15 to 20 percent of patients do not have an established vascular lesion on initial four-vessel cerebral angiography [1,2]. The causes of nonaneurysmal SAH (NASAH) are potentially diverse, and often the mechanism of bleeding in these cases is not identified.

In 1985, a subtype of NASAH, so-called perimesencephalic nonaneurysmal SAH, was identified in a case series of 13 patients who had a characteristic pattern of localized blood on computed tomography (CT), normal cerebral angiography, and a benign course that distinguished these patients from both aneurysmal SAH and other patients with nonaneurysmal SAH [3]. This observation has subsequently been confirmed by other reports [2,4-7]. It is important to recognize this pattern of bleeding, because invasive diagnostic testing can be limited in these patients and morbidity thereby reduced.

This topic reviews perimesencephalic SAH. Aneurysmal SAH and other causes of NASAH are discussed separately. (See "Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage" and "Treatment of aneurysmal subarachnoid hemorrhage" and "Nonaneurysmal subarachnoid hemorrhage".)


The reported proportion of cases of NASAH that are PM-NASAH varies between 21 to 68 percent [1,2,6,8-11]. In a biracial, population-based, epidemiologic study, the annual rate of PM-NASAH was estimated to be 0.5 per 100,000 persons over 18 years of age [8].

The mean age of occurrence of PM-NASAH in several series was between 50 and 55 years [8,12,13]. However, the age in reported cases ranges from 3 to 72 years old [1,7,14-16]. In contrast to aneurysmal SAH, there is no clear female predisposition for PM-NASAH [8,12,13].

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Literature review current through: Nov 2017. | This topic last updated: Jun 02, 2015.
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