Subarachnoid Hemorrhage

Etiology and Pathology

The rupture of a saccular (berry) aneurysm is the most common cause of a nontraumatic subarachnoid hemorrhage (SAH) (Fig. 4.26). Common sites of aneurysms are the circle of Willis at the junctions of major arteries and at their first bifurcation. Less common sites are the tip of the basilar artery and the junction of the vertebral arteries. Aneurysms vary in size from a few millimeters to 2 to 3 cm (giant aneurysms). They are often multiple, situated bilaterally as mirror images (Fig. 4.27). A ruptured saccular aneurysm commonly bleeds into the basal cisterns of the subarachnoid space, less often into the brain parenchyma or ventricles, and seldom into the subdural space.

Less common causes of SAH are mycotic (infectious) and fusiform (arteriosclerotic) aneurysms, vascular malformations, vasculopathies, and hematologic diseases (see Table 4.10).

Clinical Features

Subarachnoid hemorrhage accounts for approximately 8% of hemorrhagic strokes and is somewhat more common in younger patients and women.

Prodromal symptoms with localized, often pulsating headaches and third nerve palsy may precede the aneurysmal rupture. The highly characteristic presentation of SAH is abrupt, with severe, often excruciating headaches and meningeal signs. Altered mentation, extraocular muscle palsy, subhyaloid hemorrhage, and

Basal Subarachnoid Hemorrhage

FIGURE 4.26

Subarachnoid hemorrhage. A. Massive fresh hemorrhage in basal subarachnoid space from rupture of an anterior communicating artery aneurysm. Note the hemorrhage in the optic nerve. B and C. An anterior communicating aneurysm ruptured into the corpus callosum and ventricles.

FIGURE 4.26

Subarachnoid hemorrhage. A. Massive fresh hemorrhage in basal subarachnoid space from rupture of an anterior communicating artery aneurysm. Note the hemorrhage in the optic nerve. B and C. An anterior communicating aneurysm ruptured into the corpus callosum and ventricles.

FIGURE 4.27

Mirror image aneurysms of MCAs. A 26-year-old man underwent clipping of a ruptured left MCA aneurysm. He died at age 73 of carcinoma of the lung. A. A nonen-hanced CT scan of the head done a few weeks prior to his death shows a cherry-sized, low-density structure with a hyper-dense rim in the right Sylvian fissure. B. Base of the brain shows surgical clips in the left Sylvian fissure and a large, partially calcified and thrombosed asymptomatic right MCA aneurysm, mirror image of the ruptured left MCA aneurysm.

FIGURE 4.27

Mirror image aneurysms of MCAs. A 26-year-old man underwent clipping of a ruptured left MCA aneurysm. He died at age 73 of carcinoma of the lung. A. A nonen-hanced CT scan of the head done a few weeks prior to his death shows a cherry-sized, low-density structure with a hyper-dense rim in the right Sylvian fissure. B. Base of the brain shows surgical clips in the left Sylvian fissure and a large, partially calcified and thrombosed asymptomatic right MCA aneurysm, mirror image of the ruptured left MCA aneurysm.

Mca Aneurysm

occasionally, focal neurologic signs and seizures are present. CT scan identifies the SAH in the majority of cases, and MRA and conventional angiogram identify the aneurysm (Fig. 4.28). Mortality is high; approximately 20% of patients die within 24 hours. One-third die of the initial insult, and about one-fourth die of recurrent bleeding, frequently during the second and third weeks.

The SAH carries the risk of serious complications, notably:

• Ischemia and infarction due to vasospasm in the proximity of the bleeding aneurysm or embolization from intraluminal thrombus

• Syndrome of inappropriate antidiuretic hormone secretion (SIADH) and cardiac arrhythmias due to hypothalamic dysfunction

FIGURE 4.28

CT scan of subarachnoid hemorrhage. A. Axial nonenhanced CT scan shows acute hemorrhage in the basal cisterns and Sylvian fissures.

• Hydrocephalus, which may develop during the acute stage or several months later

TABLE 4.11.

Stroke Predisposing Diseases

in the Young

Cardiac Diseases

Vascular Diseases

Rheumatic valvular disease Mitral valve prolapse Prosthetic heart valve Congenital heart disease Myxoma

Cardiomyopathy in neuro-degenerative diseases and myopathies

Fibromuscular dysplasia Arterial dissection Systemic lupus erythematosus Vascular malformation Takayasu's arteritis Moyamoya disease Vasculopathy secondary to illicit substances Inherited vascular diseases Early atherosclerosis

Hematologic Diseases

Inherited Metabolic Diseases

Sickle cell disease Thrombotic thrombocytopenia Hemophilia Leukemia Antiphospholipid antibody syndrome Venous thrombosis

Homocystinuria MELAS; Mitochondrial Encephalomyopathy, Lactic acidosis, Stroke-like Episodes Fabry's disease

During the acute stage, the circulation and absorption of the cerebrospinal fluid (CSF) is obstructed by the hemorrhage and, during the chronic stage, by fibrotic adhesions between the arachnoid and pia.

Cerebral aneurysm often coexists with cerebral and visceral vascular malformations, moyamoya disease, polycystic kidneys, pancreatic cysts, fibromuscular dysplasia, coarctation of the aorta, and Ehlers-Danlos and Marfan syndromes (see next section, Various Stroke Etiologies).

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