I. Etiology and pathogenesis
1.Etiology
(1) Intracranial aneurysm: It is the most common cause (about 50%-80%). Among them, congenital cornea aneurysm accounts for about 75%. It can also be seen in hypertension, atherosclerosis caused by cloacal aneurysm and fungal aneurysm caused by infection, etc.
(2) Vascular malformation: It accounts for about 10% of the causes of SAH. Among them, arteriovenous malformation (AVM) accounts for 80% of vascular malformations. It is mostly seen in young people, and more than 90% of them are located on the curtain, commonly in the middle cerebral artery distribution area.
(3) Others: such as moyamoya disease (20% of SAH in children), intracranial tumors, pituitary stroke, hematologic disorders, intracranial venous system thrombosis, and complications of anticoagulation therapy. In addition, the etiology is unknown in about 10% of patients.
2.Pathogenesis
(1) Aneurysm: cornu-like aneurysm may be related to genetic and congenital developmental defects. Autopsy found that the elastic layer of the wall of the circumflex artery of Willis and the middle membrane are abnormal or damaged in about 80% of patients, and the elasticity of the arterial wall decreases with age due to atherosclerosis of the arterial wall, hypertension and blood vortex impact. The weakness of the wall gradually expands and protrudes outward to form a saccular aneurysm. Inflammatory aneurysms are lesions of the vessel wall caused by arteritis or intracranial inflammation.
(2) Cerebral arteriovenous malformation: It is a malformed vascular mass formed by developmental abnormalities, and the weakness of the vessel wall is in the critical state of rupture, and agitation or insignificant inducement leads to rupture.
(3) Other: such as tumor or metastatic cancer directly erode the blood vessel, causing the vessel wall lesion, and eventually lead to rupture and bleeding.
Pathology
Aneurysms are mainly located in the ring of Willis and its main branch vessels, especially at the bifurcation of arteries. 80%-90% are located in the anterior part of the arterial ring of the base of the brain, especially at the junction of the posterior communicating artery and the internal carotid artery (about 40%), at the bifurcation of the anterior communicating artery and the anterior cerebral artery (about 30%), and at the first major branch of the middle cerebral artery in the lateral fissure (about 20%). Posterior circulation aneurysms are most commonly found at the tip of the basilar artery or at the junction of the vertebral artery and the posterior inferior cerebellar artery, and are mostly solitary, with about 20% being multiple and located in the same artery on both sides (also known as “mirror aneurysms”).
The size of the aneurysm is related to the rupture. Aneurysms larger than 10 mm in diameter are prone to bleeding; aneurysms that are irregular or polycystic in shape and located in the dome are prone to rupture. Arteriovenous malformations are formed by abnormal vascular traffic and are commonly found in the middle cerebral artery distribution. Subarachnoid hemorrhage can be seen as purplish-red blood deposited in the fundic and spinal pools, such as the suprasellar pool, pontocerebellar peduncle pool, circumflex pool, cerebellar medullary pool, and terminal pool. In the case of large amounts of hemorrhage, a thin layer of blood clot was formed to cover the skull base vessels, nerves and brain surface, and the arachnoid membrane showed a sterile inflammatory reaction and soft membrane thickening, resulting in adhesion of brain tissue to vessels or nerves. Extensive white matter edema in the brain parenchyma and multiple patches of ischemic foci are seen in the cortical division.
The pathophysiology can cause a series of pathophysiological changes.
1. Blood flow to the subarachnoid space stimulates nociceptive sensitive structures causing headache. Increased ICP due to increased intracranial volume can exacerbate the headache. It can lead to subretinal hemorrhage in the vitreous and even brain herniation.
2.The cerebral blood flow drops sharply when intracranial pressure reaches the systemic perfusion pressure, and the shock effect accompanying the rupture of a hemangioma may be the cause of loss of consciousness at the onset in about 50% of patients.
3, Blood clotting in the skull base or brisket chamber obstructs CSF return, and acute obstructive hydrocephalus develops early in 30%-70% of patients, with hemoglobin and iron-containing blood. The deposition of flavin in the arachnoid granules can also lead to obstruction of CSF reflux, traffic hydrocephalus and ventricular dilatation.
4, subarachnoid blood cells disintegrate and release various inflammatory substances causing chemical meningitis, and increased CSF increases ICP.
5.Blood and decomposition products blood contact stimulation cause hypothalamic dysfunction, such as fever, elevated blood sugar, acute myocardial ischemia and U arrhythmia.
6.The vasoactive substances released from blood such as 5-HT, thromboxane A2 (TXA2) and histamine stimulate blood vessels and meninges, causing vasospasm and, in severe cases, cerebral infarction.
7.Aneurysm bleeding is often limited to the subarachnoid space and does not cause focal annoyance damage, and focal signs are rarely found in neurological examination. Unless the middle cerebral artery aneurysm, another arteriovenous malformation rupture commonly causes focal abnormalities.
Clinical manifestations
Most patients have emotional excitement, straining, defecation, coughing and other triggers before the onset of hemorrhagic symptoms. The onset of hemorrhage is sudden, with severe headache, nausea and vomiting, pallor, and generalized cold sweat. Half of the patients may have psychiatric symptoms, such as agitation, confusion, disorientation, etc. The patient may have a convulsion after bleeding in 20% of cases. Some patients may also experience vertigo, collar and back pain or lower limb pain. Meningeal irritation signs are apparent, often within 1-2 days after subarachnoid space hemorrhage. After symptomatic treatment of the hemorrhage, most patients gradually stabilize, their consciousness and vital signs improve, and the symptoms of meningeal irritation decrease.
After the first rupture and bleeding of an intracranial aneurysm, some patients may bleed again or three times if they are not treated appropriately and in a timely manner. Patients die from rebleeding in about 1/3 of cases. cerebral nerve damage is common with one side of the arterial nerve palsy, accounting for 6–20% of cases, suggesting the presence of ipsilateral internal carotid artery a posterior communicating artery aneurysm or posterior cerebral artery aneurysm. Hemiparesis occurs before and after hemorrhage in about 20% of cases with hemiparesis and mild hemiparesis. This is due to lesions or hemorrhage involving the motor cortex and its conduction tracts.
Visual field impairment Subarachnoid hemorrhage may extend along the optic nerve sheath, and funduscopic examination reveals a subvitreal lumpy hemorrhage, which may appear within 1 hour of onset, which is strong evidence for the diagnosis of subarachnoid space hemorrhage. When the hemorrhage is excessive, the blood may soak into the vitreous and cause visual impairment. 10–20% of the hemorrhages are seen as optic papillary edema. Bilateral or synoptic hemianopia occurs when the optic cross, bundle, or radiation is involved. Intracranial arteriovenous malformations and intracranial aneurysms may cause intracranial murmurs in about 1% of cases. Some subarachnoid hemorrhages may have hypothermia for several days after the onset.
IV. Examination
CT of the head is nearly 100% accurate in diagnosing acute SAH. The CT shows the clearest picture within the first week after bleeding, and the bleeding is gradually absorbed after 1-2 weeks. It shows increased density of cerebral sulcus and brain pool. The ruptured internal carotid aneurysm bleeds most frequently in the lateral cerebral fissure. Blood from a ruptured middle cerebral aneurysm accumulates in the affected lateral fissure and may also flow to the circumferential and longitudinal fissure pools. After rupture of basilar aneurysm, blood mainly accumulates near the interpeduncular pool and circumferential pool.
In addition, CT can show intracerebral (ventricular) hematoma, hydrocephalus, cerebral infarction and cerebral edema, and CTA can show cerebrovascular malformations and aneurysms, which is a noninvasive and easy test.
Acute SAH within one week after the onset of head MRI is difficult to detect in MRI. Magnetic resonance angiography (MRA) is a non-invasive cerebrovascular imaging method and can be used as a screening tool for diagnosis of head, neck and intracranial vascular diseases.
Early examination of cerebral angiography can promptly clarify the size, location, single or multiple aneurysms, the presence of vasospasm; the supply arteries and draining veins of arteriovenous malformations, and the collateral circulation. Spinal arteriography should also be performed for suspected spinal arteriovenous malformations. Digital subtraction angiography (DSA) has a high diagnostic value for cerebrovascular disease.
Lumbar puncture is no longer necessary for SAH diagnosed by CT, because SAH with increased intracranial pressure may induce brain herniation. In case of SAH caused by aneurysm rupture, lumbar puncture may also cause the risk of re-rupture and bleeding of the aneurysm.
V. Diagnosis
Sudden onset of severe headache, vomiting, positive meningeal irritation signs with or without impaired consciousness, and no focal neurological signs on examination should highly suspect subarachnoid hemorrhage. The diagnosis should be confirmed clinically by CT confirming high density signs in the brain pool and subarachnoid space or lumbar puncture showing increased pressure and bloody cerebrospinal fluid.
1.Differential diagnosis
Hypertensive cerebral hemorrhage: bloody cerebrospinal fluid may also be present, but there should be obvious focal signs such as hemiparesis and aphasia at this time. Primary ventricular hemorrhage is clinically difficult to distinguish from patients with severe SAH. Cerebellar hemorrhage and caudate nucleus head hemorrhage are also clinically easy to confuse with SAH because there is no obvious limb paralysis, but CT and DSA examination can distinguish.
2.Picture description
(1) Intracranial infection: bacterial, fungal, tuberculosis and viral meningitis can have headache, vomiting and meningeal irritation signs. When chemical meningitis occurs after SAH, CSF leukocytosis is easily confused with infection, but the latter is preceded by fever. when SAH cerebrospinal fluid yellowing and lymphocytosis are present, it is easily confused with tuberculous meningitis, but the latter has reduced CSF sugar and chloride and normal head CT.
(2) Brain tumor: about 1.5% of brain tumor strokes occur in the mouth of the tumor, forming intratumoral or paratumoral hematoma combined with SAH; intracranial metastasis of carcinoma, meningeal carcinomatosis or CNS leukemia can also be seen as bloody CSF. but can be differentiated based on detailed medical history, CSF detection of tumor/carcinoma cells and head CT.
(3) Others: In some elderly patients, headache and vomiting are not obvious, but sudden mental disturbance is the main symptom, which should be noted in clinical work.
VI. Treatment
The purpose of treatment in the acute phase is to prevent and control rebleeding, reduce intracranial pressure, prevent and control secondary cerebral vasospasm, reduce complications, find the cause of bleeding, treat the original disease and prevent recurrence.
1.Medical treatment
General treatment: Patients with SAH should be treated with emergency inpatient supervision and absolute bed rest for 4-6 weeks. Avoid moving and leaving the bed prematurely, elevate the head of the bed by 15°～20°, and keep the ward quiet, comfortable and dark light. Avoid triggers that cause increased blood pressure and cranial pressure, such as forceful defecation, coughing, sneezing, emotional excitement, pain and fear, etc. Targeted application of laxatives, cough suppressants, sedatives and analgesics can be used to avoid triggering re-rupture of the aneurysm. Be cautious with non-steroidal drugs such as aspirin and other town can affect the coagulation function or morphine, pethidine and other drugs that may affect the respiratory function. After removing the cause of headache, patients with mean arterial pressure >120 mmHg or systolic pressure >180 mmHg can use short-acting antihypertensive drugs under the condition of close monitoring of blood pressure to maintain the blood pressure stable at normal or pre-onset level. Patients with convulsions are treated with antiepileptic therapy. Saline is given in appropriate amounts to ensure normal blood volume and adequate cerebral perfusion. Hyponatremia is common and may be treated with oral or intravenous saline. Fluids should not be restricted. Cardiac monitoring to prevent arrhythmias, attention to nutritional support, prevention of complications, etc.
Causes increased intracranial pressure: Appropriate restriction of fluid intake, prevention of hyponatremia, hyperventilation, etc. can help reduce intracranial pressure. Clinically, 20% mannitol, furosemide and albumin are commonly used to lower the intracranial pressure. For those with obvious signs of intracranial hypertension and the tendency of brain herniation, ventricular drainage is feasible to save the patient’s life.
Prevention of rebleeding: antifibrinolytic drugs can inhibit the formation of fibrinolytic enzymes, delay the dissolution of clots and prevent rebleeding.
Aminocaproic acid: 4-6g in 0.9% saline lOOml intravenously for 15-30 minutes, then lg/h for 12-24 hours; after that 24g/d for 3-7 days, gradually reduce the dose to 8g/d. Maintain for 2-3 weeks. Use with caution in renal dysfunction. Pay attention to adverse reactions such as deep vein thrombosis and cerebral ischemia, which require simultaneous co-application of calcium antagonists.
Aminobenzoic acid: 0.1-0.2g dissolved in 5% glucose solution or saline, slowly injected 2-3 times/d.
Lithophoresis: 2kU/dose. 5-10 minutes to take effect, the effect lasts 24 hours. However, the application of hemostatic agents is still controversial, and the application process may cause cerebral ischemic lesions, usually to be combined with nimodipine. Aneurysmal SAH can also be treated by early surgical clamping of the aneurysm or interventional embolization.
Prevention of vasospasm: SAH complicated by arterial spasm and cerebral infarction is another major cause of death due to aggravation of the disease, and once spasm occurs, especially late cerebral vasospasm, it is difficult to reverse, so prevention is important. Currently, the clinical use of calcium channel antagonists, such as nimodipine 40-60mg/time. 4-6 times/day for 21 days, can reduce the rate of poor regression and ischemic neurological deficits after aneurysmal SAH, while the efficacy of other oral or intravenous calcium antagonists is uncertain. 3H therapy, i.e. hemodilution, hemodilution and hypertension therapy to prevent vasospasm, should be used when cerebral infarction and intracranial hypertension have been excluded. intracranial hypertension, and after clamping of the aneurysm.
Cerebrospinal fluid release therapy: It is used for patients with acute hydrocephalus after SAH with dilated ventricular blood accumulation or formation of casts, worsening symptoms with conservative medical treatment, accompanied by impaired consciousness, or elderly patients with severe cardiac, pulmonary, renal and other organ dysfunction that cannot tolerate craniotomy. Each release of CSF 10-20ml twice a week can promote blood absorption, relieve headache and reduce cerebrovascular spasm. However, the risk of brain herniation, intracranial infection and rebleeding should be guarded against, and the indications should be strictly controlled. There is a lack of information to support large-scale, multicenter, randomized, roost-controlled studies.
2.Surgical treatment
The aim is to eradicate the cause of the disease and prevent recurrence.
Aneurysm: The elimination of aneurysm is the best way to prevent rebleeding of aneurysmal SAH. Surgical treatment often uses aneurysm neck clamping, atherectomy and aneurysm embolization. The Hunt and Hess grading method is useful for determining the timing of surgery and prognosis; surgery for patients with Hunt grade I, II or mild grade III can improve clinical regression, while surgery for patients with grade IV or V is not recommended. The optimal timing of surgery remains controversial, but recent evidence supports early surgery (within 96 hours of bleeding) to shorten the period of risk of rebleeding and to allow treatment of vasospasm with volume expansion and pressure-raising agents. The management of asymptomatic, surgically ruptured aneurysms >5 cm is controversial. The benefits of surgery (reduced incidence of bleeding) outweigh the risks, and asymptomatic small aneurysms are suitable for conservative treatment. Endovascular spring coil embolization of ruptured saccular aneurysms has gained worldwide popularity in recent years. Current studies have found a significant reduction in the relative and absolute risk of intervention over surgical treatment.
Arteriovenous malformations: AVM whole-block resection, blood supply artery ligation, endovascular interventional embolization or ? knife treatment, etc. Since the risk of early rebleeding of AVM is much lower than that of aneurysm, surgery can be performed electively
VII. Prognosis
The prognosis is related to the etiology, bleeding site, bleeding volume, the presence of complications, and the availability of appropriate treatment. Aneurysmal SAH has a high mortality rate, with approximately 12% of patients dying before arrival at the hospital and 20% dying after admission. 2/3 of patients will survive, but half of them will have permanent disability, mainly cognitive impairment. Approximately 20% of those without surgical treatment die from rebleeding, with death occurring mostly in the first few days after bleeding. 90% of patients with intracranial AVM rupture recover with a low risk of rebleeding.