bubble_chart Overview

Blood from ruptured blood vessels directly enters the subarachnoid space, known as primary subarachnoid hemorrhage (SAH). Trauma-induced cases are called traumatic SAH. Cases without obvious causes such as trauma are referred to as spontaneous SAH, which is the focus of this discussion. When intracerebral hemorrhage breaks through the brain parenchyma to the brain surface or enters the ventricles and reaches the subarachnoid space, it is termed secondary SAH.

bubble_chart Etiology

80% of spontaneous SAH results from the rupture of stirred pulse aneurysms. The second most common cause is arteriovenous malformation (AVM). In Perret et al.'s report of 6,365 cases of SAH, 549 were AVMs, accounting for 8.6%.

Over 90% of intracranial stirred pulse aneurysms are saccular stirred pulse aneurysms, located at the bifurcations of major stirred pulse vessels at the base of the brain, rupturing into the subarachnoid space of the basal cisterns. The most common sites include the junction of the anterior communicating stirred pulse and the anterior cerebral stirred pulse, the junction of the posterior communicating stirred pulse and the internal carotid stirred pulse, the bifurcation of the middle cerebral stirred pulse, the apex of the basilar stirred pulse, the junctions of the basilar stirred pulse and its major branches, and the junction of the vertebral stirred pulse and the posterior inferior cerebellar stirred pulse. 85–90% occur in the anterior part of the circle of stirred pulse at the base of the skull. 12–31% of stirred pulse aneurysms are multiple, mostly distributed in mirror positions. Saccular stirred pulse aneurysms may result from a combination of congenital, genetic, and acquired factors (such as stirred pulse atherosclerosis and hypertension).

Atherosclerotic stirred pulse aneurysms, also known as fusiform stirred pulse aneurysms, account for approximately 7% of intracranial stirred pulse aneurysms. They are most commonly found in the basilar stirred pulse but can also occur in the internal carotid stirred pulse, middle cerebral stirred pulse, etc. The affected stirred pulse vessels become tortuous, thickened, and elongated, rarely rupturing. Symptoms arise due to compression, emboli, or obstruction of cerebrospinal fluid pathways.

Infectious stirred pulse aneurysms account for about 1% of intracranial stirred pulse aneurysms. Unlike saccular stirred pulse aneurysms, which typically occur at major stirred pulse bifurcations, infectious stirred pulse aneurysms mostly develop in the distal branches of the middle cerebral stirred pulse or anterior stirred pulse and are often multiple. They form due to weakening of the vessel wall by infectious emboli, followed by rupture of the stirred pulse aneurysm, leading to SAH.

AVM is a congenital developmental anomaly of arteriovenous fistulas. Small ones may measure only a few millimeters, while others can grow over time into a tangled mass of tortuous, dilated vessels, with arteriovenous shunting so significant that it increases cardiac output. Dilated, hypertrophied feeding stirred pulse vessels enter the lesion from the brain surface and disperse into a network of thin-walled vessels in the subcortical region, bypassing the normal capillary network and directly draining into veins. The direct influx of stirred pulse blood causes these abnormally thin-walled vessels to enlarge, dilate, and become pulsatile. AVMs can occur anywhere in the brain and spinal cord but are more commonly found in the frontal-parietal region of the brain, appearing wedge-shaped with the base at the cortex and the apex toward the ventricle. Some are large enough to cover an entire cerebral hemisphere. Due to vascular malformations and thinning of the vessel walls, they eventually rupture, causing SAH or intracerebral hemorrhage, often both. Approximately 10% of patients also have intracranial stirred pulse aneurysms.

In extremely rare cases, SAH is caused by the rupture of spinal AVMs or intraspinal stirred pulse aneurysms.

Intracranial stirred pulse aneurysms or arteriovenous malformations can rapidly increase intracranial pressure when blood rushes into the subarachnoid space due to vessel wall rupture. Patients may lose unconsciousness as if experiencing a concussion or even suffer sudden death due to brain displacement affecting the brainstem. Blood irritation causes aseptic meningitis, manifesting not only as severe headache but also hypertension and arrhythmias due to stimulation of the sympathetic-adrenal system. Blood clots and irritation lead to excessive exudate secretion by the meninges, causing arachnoid adhesions. Obstruction of cerebrospinal fluid pathways or blockage of arachnoid granulations near the sagittal sinus, which absorb cerebrospinal fluid, can result in subacute or chronic hydrocephalus. Rupture of stirred pulse aneurysms and blood irritation can both cause stirred pulse spasms, compounded by vessel wall edema or thrombosis, leading to severe ischemia in the supplied brain tissue and resulting in cerebral infarction, manifesting as focal neurological deficits such as hemiplegia. Blood may also enter the brain parenchyma, ventricles, or subdural space.

After subarachnoid hemorrhage, blood clots coagulate in the cisterns and on the brain surface. The disintegration of red blood cells releases hemosiderin, which can stain the cerebral cortex and arachnoid membrane a rusty red color. When removing the clot, the exposed arterial wall may sometimes reveal a small red dot at the rupture site; however, due to extensive damage, this is often nearly unrecognizable. Under the microscope, phagocytosis of red blood cells by arachnoid membrane cells and free mononuclear cells can be observed. Fibroblasts from the pia mater and adventitia infiltrate the clot, leading to its organization and eventual formation of subarachnoid space occlusion and scar tissue. Additionally, signs of the primary lesion causing the hemorrhage may also be observed.

bubble_chart Clinical Manifestations

The decision depends on the size and location of the stirred pulse tumor. The chance of rupture is low for stirred pulse tumors with a diameter less than 1 cm. More than 50% of cystic stirred pulse tumors develop after the age of 40. The incidence of stirred pulse tumor rupture is highest between the ages of 35 and 65.

Some patients experience precursor symptoms before SAH, which have localizing significance and indicate that the stirred pulse tumor has expanded to a certain extent, compressing adjacent neural structures. Oculomotor nerve palsy with pupil dilation, loss of light reflex, and pain behind the eyebrow or eye suggests that the posterior communicating stirred pulse tumor originating from the internal carotid stirred pulse has expanded to 7 mm or larger. Expansion of stirred pulse tumors in the cavernous sinus can cause abducens nerve palsy. Stirred pulse tumors on the supraclinoid internal carotid stirred pulse can compress the optic nerve or chiasm, leading to visual and field disturbances.

It remains uncertain whether small amounts of blood may intermittently leak into the subarachnoid space before stirred pulse tumor rupture. However, timely diagnosis of minimal rupture or leakage is critically important. Unexplained sudden headache in any part of the head should raise suspicion of SAH, especially when the headache radiates to the neck or back and is accompanied by nausea and vomiting. Minor SAH may yield negative CT results and require lumbar puncture for confirmation.

Most stirred pulse tumor ruptures occur during daily activities, and some are triggered by exertion or emotional excitement. At the moment of rupture, intracranial pressure approaches the mean stirred pulse pressure, and cerebral perfusion pressure drops, causing transient loss of consciousness. Severe headache may precede unconsciousness. Most patients report headache only after regaining consciousness. A few patients may remain unconscious for days due to severe SAH. About half of the patients present with severe headache without impaired consciousness. Pain starting in the frontal region suggests supratentorial hemorrhage, while pain in the occipital region suggests infratentorial hemorrhage, often corresponding to the side of the stirred pulse tumor rupture. Vomiting is a prominent symptom. Patients often exhibit significant photophobia, sound sensitivity, and refusal to move.

Unilateral oculomotor nerve palsy mostly indicates a posterior communicating stirred pulse tumor. Abducens nerve palsy has little localizing value. If hemiplegia, aphasia, or anosognosia appears shortly after onset, it suggests intracerebral hematoma, large subdural hematoma, or subarachnoid hematoma. If these lateralizing signs appear days after onset without new bleeding, localized cerebral ischemia or infarction due to vasospasm should be considered. If consciousness gradually declines days after onset without worsening focal neurological symptoms, it may indicate hydrocephalus and increased intracranial pressure.

In rare cases, the condition is critical, with rapid progression to deep unconsciousness or even respiratory arrest and death, resulting from brain herniation and brainstem compression following subarachnoid hemorrhage.

Neck stiffness is a common sign but may appear as late as 12–24 hours after onset, related to the time required for meningeal inflammatory reaction. Marked neck stiffness at onset warrants vigilance for foramen magnum tonsillar herniation and the risk of respiratory arrest; lumbar puncture is contraindicated in such patients! Clinically, the absence of meningeal irritation signs does not completely rule out SAH. Fundus examination may reveal small spherical hemorrhages near the optic disc or in the preretinal (subhyaloid) space, possibly with early signs of papilledema.

Patients may develop low-grade fever, glycosuria, proteinuria, and elevated white blood cell counts. Massive release of Black Catechu phenols into the circulation can cause multifocal micro-necrosis of the myocardium, with ECG showing abnormalities resembling myocardial infarction. Some patients may experience renal salt wasting, excessive secretion of antidiuretic hormone (ADH), or acute pulmonary edema.

Nearly half of AVMs present with SAH as the initial symptom, resembling the rupture of a stirred pulse aneurysm. The average age of onset is younger than that of stirred pulse aneurysms, with most cases occurring between 20 and 30 years old. Most AVMs are located intracerebrally, and after rupture, the amount of intracerebral hemorrhage often exceeds that in the subarachnoid space. In addition to headache and meningeal irritation signs, focal neurological deficits such as hemiplegia, aphasia, and hemianopia are commonly observed. Since most AVMs rupture from veins, the bleeding is less severe than that from saccular stirred pulse aneurysms. Blood escapes from the brain surface rather than directly flooding into the basal cisterns as in stirred pulse aneurysm rupture, so the chance of major basal stirred pulse vasospasm is low. The headache at onset is less common and less severe than the SAH headache caused by stirred pulse aneurysm rupture. There may be minimal bleeding or bleeding in non-critical functional areas, resulting in no focal symptoms. Alternatively, massive hemorrhage or primary intraventricular hemorrhage may lead to unconsciousness shortly after headache and acute death. 20–40% of AVMs present with epilepsy as the initial symptom, either focal or generalized seizures. Among 90 cases of AVM-related epilepsy, 15% experienced intracranial hemorrhage within one year. 7–15% of AVMs present with both seizures and intracranial hemorrhage as the initial symptoms, with vascular lesions mostly involving the cerebral surface, particularly the central and parietal regions. 10% of AVMs present with headache as the initial symptom, manifesting as migraine or recurrent unilateral headache. However, many recent studies have failed to establish any definitive link between headache and AVMs.

In approximately 40% of AVMs, particularly those in the internal carotid artery-pulse-cerebral artery-pulse system with large AVMs, vascular murmurs can be heard over the eyeball or skull. In saccular pulse aneurysms, murmurs are usually not audible.

bubble_chart Auxiliary Examination

(1) CT Immediate CT scanning after onset can detect blood clots in the adjacent cisterns or cerebral fissures, intracerebral or subdural hematomas, and whether hydrocephalus is present in over 90% of cases of ruptured aneurysms or AVMs. Blood clots larger than 5×3 mm² in the cisterns or a 1 mm-thick layer of blood in the cerebral fissures can be detected by CT (Figure 24-5). However, the detection rate for posterior fossa hematomas is not high. Some cases of SAH visible on CT within hours of onset may show negative results 24 hours later. CT becomes unreliable after 96 hours. Enhanced CT should only be performed in patients who have already undergone standard CT and can help visualize aneurysms or AVMs.

(2) Magnetic Resonance Imaging (MRI) MRI is not reliable for diagnosing SAH. In cases of SAH, it is primarily used to detect cerebral infarction secondary to vasospasm. After the absorption of intracerebral hematomas caused by AVMs, MRI may indicate the presence of an AVM.

(3) Cerebrospinal Fluid Lumbar puncture for cerebrospinal fluid examination is only performed when CT is unavailable or when CT shows no evidence of SAH but clinical suspicion remains. However, the patient must not exhibit signs of intracranial mass lesions. A fine needle should be used. Cerebrospinal fluid pressure is often elevated above 19.6 kPa (200 mm H₂O). The fluid should be collected in three tubes. Cell counts should be performed on the first and last tubes. If the red blood cell counts are the same in both tubes, it indicates SAH. If the first tube has significantly more red blood cells than the last, it suggests traumatic hemorrhage from the puncture. After centrifugation, xanthochromia of the supernatant indicates SAH occurring at least 2 hours prior. Xanthochromia results from the release of oxyhemoglobin due to red blood cell membrane breakdown, which is subsequently metabolized into bilirubin. If lumbar puncture is performed days or weeks after onset, the cerebrospinal fluid may show reactive leukocytosis. Protein levels may increase to 80–100 mg/dl.

(4) Cerebral Angiography This is the definitive method for diagnosing aneurysms and AVMs. Selective catheter cerebral angiography is currently the standard examination for diagnosing cerebral aneurysms, with a positive rate of 75–80%. Except for patients with severe hemiplegia accompanied by confusion or deep unconsciousness, who are not suitable for immediate angiography or surgery, angiography should be performed as early as possible.

(5) Transcranial Doppler (TCD) TCD is a non-invasive technique for measuring blood flow velocity in the major cerebral arteries at the base of the skull. In cases of SAH, it can replace cerebral angiography as a method for detecting cerebral vasospasm. Angiography and aneurysm clipping should ideally be performed before vasospasm develops. Once vasospasm occurs, cerebral perfusion pressure can be controlled and increased under TCD monitoring to prevent cerebral ischemia. TCD can also non-invasively diagnose AVMs based on characteristic changes in blood flow velocity in the feeding arteries.

bubble_chart Diagnosis

First, to confirm whether it is SAH, further determination of the disease cause of SAH is needed.

Any sudden onset of severe headache accompanied by changes in consciousness, mental state, and/or signs of meningeal irritation should prompt a cranial CT scan. If the cranial CT is negative and there are no signs of intracranial space-occupying lesions, a lumbar puncture for cerebrospinal fluid (CSF) examination should be performed. If the CSF contains blood but the red blood cell count in the final tube is lower than in the first tube, the centrifuged fluid is clear, and the CSF coagulates quickly in the test tube, it indicates traumatic hemorrhage from the puncture. Otherwise, it is SAH. Further differentiation is needed to determine whether it is primary SAH or secondary SAH. In cases of secondary SAH due to hypertensive cerebral hemorrhage, the headache at onset is less sudden and severe compared to primary SAH, and most patients exhibit obvious focal neurological symptoms from the outset, such as the "three biases" symptoms of capsular hemorrhage.

The main causes of primary SAH are intracranial aneurysms and arteriovenous malformations (AVM). If there were no neurological symptoms before the illness or if oculomotor or abducens nerve palsy occurs afterward, consider an aneurysm. If there is a history of epileptic seizures before the illness, relatively mild meningeal irritation signs, focal brain symptoms immediately after onset, or CT showing hemorrhage on the brain surface rather than at the skull base, consider an arteriovenous malformation. In rare cases, vascular rupture into the subarachnoid space may be the first symptom of pituitary adenoma, glioma, cerebellar hemangioblastoma, cerebral metastatic cancer, or tuberculous meningitis. Diagnosis can only be confirmed through CT, angiography, or CSF examination.

Hematologic or coagulation disorders can also cause SAH, but symptoms of the primary disease are almost always present before the onset. A thorough medical history and comprehensive physical examination should identify the issue.

bubble_chart Treatment Measures

The key is to prevent rebleeding and manage vasospasm and its secondary cerebral infarction.

(1) Preoperative Care Surgical treatment is definitely superior to bed rest alone in preventing rebleeding. However, before surgery, patients should rest quietly and avoid any form of exertion. Laxatives or mild cathartics should be used to maintain bowel regularity. A low-residue diet can help reduce stool volume. Severe headache can be treated with analgesics and sedatives. Aspirin, due to its antiplatelet aggregation effect, may trigger rebleeding and should be avoided. Maintain water and electrolyte balance to prevent dehydration, which increases the risk of cerebral ischemia. Adequate cerebral perfusion pressure must be maintained. Monitor blood gases and provide assisted ventilation if hypercapnia is detected. Anticonvulsants may be given to prevent seizures that could lead to rebleeding. The effectiveness of antihypertensive drugs is uncertain, and maintaining cerebral perfusion pressure is the priority.

(2) Antithrombotic Therapy This is suitable for patients who cannot undergo surgery. It may reduce the rebleeding rate but increases the incidence of cerebral infarction, so the overall prognosis is not improved.

(3) Surgical Treatment In recent years, there has been a trend toward performing surgery within 1–3 days after onset, especially for mild or grade II patients. Patients in a stupor or deep unconsciousness are not suitable for acute-phase surgery unless the progression of intracranial hematoma is life-threatening. The risk of re-rupture and cerebral vasospasm is highest within 3 weeks after aneurysm rupture. Therefore, patients who are conscious, have no focal neurological deficits, and whose condition has stabilized for 1–2 days, as well as those with initial grade I impairment or focal symptoms that are improving, should undergo early surgery if there are no signs of cerebral vasospasm.

(4) Calcium Channel Blockers Nimodipine and nicardipine, administered orally or systemically, can be used to prevent and treat cerebral vasospasm. The latter typically occurs 3–5 days after SAH and peaks in severity between 5–14 days, potentially causing cerebral infarction and death in 15% of patients. For patients at risk of cerebral vasospasm, prophylactic treatment with nimodipine should last at least 3 weeks.

(5) Hydrocephalus Acute hydrocephalus occurs within 3 days in 25% of SAH cases, and by 30 days, about 60% of patients develop chronic ventricular enlargement. For acute hydrocephalus with declining consciousness after SAH, ventricular drainage is recommended, but infection must be prevented. Most patients with chronic ventricular enlargement are asymptomatic, and ventriculoperitoneal shunting is only effective for some.

bubble_chart Prognosis

10-50% of SAH patients die during the first attack, with a 5-year survival rate of 50-85%. Prognosis is poor for those diagnosed with intracranial stirred pulse aneurysms or arteriovenous malformations, while SAH with unknown causes has a better prognosis. In long-term prognosis studies of SAH of unknown origin, the survival rate in the hypertensive group was significantly lower than in the normotensive group.

Among patients who survive the first SAH attack, 5-30% experience a second SAH, with a mortality rate of 30-60%. More than one-third of recurrent survivors will have a third attack. The mortality and rebleeding rates of recurrent SAH are higher than those of the first attack. The risk of rerupture is greatest within 2 weeks after the rupture of an intracranial stirred pulse aneurysm, but recurrence can occur as late as 15-20 years later.

Arteriovenous malformations are usually located within the brain, and functional outcomes are worse than those of stirred pulse aneurysms. Some patients may develop arachnoid membrane adhesions in the late stage [third stage], obstructing cerebrospinal fluid flow and causing hydrocephalus.

In one group followed for an average of over 4 years, more than 90% of survivors could work or study normally, 2 cases could partially care for themselves, and 1 case required complete nursing care due to dementia.