I. Overview of subarachnoid hemorrhage When a cerebral hemangioma ruptures and bleeds, blood flows into the subarachnoid space, causing the cerebrospinal fluid to become bloody, which is called subarachnoid hemorrhage. The most common cause of hemorrhage is a ruptured congenital aneurysm, followed by atherosclerosis and vascular malformation. Sometimes, cerebral hemorrhage causes blood to flow into the ventricles of the brain or to penetrate the cortex and reach the subarachnoid space, which is called secondary subarachnoid hemorrhage. It can be seen that subarachnoid hemorrhage is not an independent disease but a combination of many causes. Among them, congenital cerebral aneurysm is the most common cause. Brain aneurysm, also called intracranial aneurysm, is not a real tumor, but a particularly weak local area in the blood vessel wall of the intracerebral artery, which gradually expands outward under long-term blood flow impact, forming a small balloon-like hemangioma. The higher the local blood flow pressure, the higher the risk of rupture of the aneurysm. When rupture occurs, blood enters the surrounding tissue. Sometimes the aneurysm does not rupture, but because of its increased size, it can compress nearby nerves, causing the corresponding symptoms. It is estimated that as many as 1 in 100,000 people in the United States will have a brain aneurysm in their lifetime. Brain aneurysms can occur at any age, but the most common age is 35-60. Causes of cerebral aneurysm: congenital malformation; hypertension or intracerebral atherosclerosis; cerebral thrombosis; certain types of infection (also called bacterial aneurysm); trauma to the head; heredity; drug addiction, such as cocaine. IV. Classification of cerebral aneurysms They can be classified as congenital saccular aneurysms, cloacal aneurysms due to atherosclerosis, bacterial aneurysms due to infection, traumatic aneurysms after trauma, and entrapment aneurysms due to arterial wall separation, etc. Saccular aneurysms are common and vary in size, with those less than 14 mm in diameter being small, those between 15 and 24 mm being large, and those over 25 mm being giant. Trauma can also cause aneurysms, but they are less common. Cerebral aneurysms are mostly found at the bifurcation of the basilar artery. According to the location, 4/5 of them are located in the anterior half of the cerebral artery ring, mostly in the internal carotid artery, posterior communicating artery and anterior communicating artery, and also in the branches of middle cerebral artery or anterior cerebral artery; about 1/5 of them are in the posterior half of the cerebral artery ring, occurring in the vertebrobasilar artery, posterior cerebral artery and their branches. V. Symptoms 80% to 90% of spontaneous subarachnoid hemorrhage is caused by aneurysm rupture. When an aneurysm ruptures, there are often prodromal symptoms such as headache, followed by hemorrhagic symptoms such as severe headache, irritability, nausea and vomiting and other signs of meningeal irritation, followed by an increase in intracranial pressure. This may be accompanied by impaired consciousness and neurological localization of the corresponding area. Depending on the amount of hemorrhage and the location of the aneurysm, there may be specific neurological signs, such as internal carotid artery-posterior communicating artery aneurysm hemorrhage, which may be accompanied by ipsilateral arteriovenous nerve palsy (eyelid ptosis, limited eye movements, and dilated pupils). If the aneurysm bleeds and forms a large hematoma, the condition deteriorates sharply and brain herniation crisis occurs. According to statistics, after the first rupture of an aneurysm, the mortality rate is as high as 30-40%, half of them die within 48 hours after the onset of the disease, and in 1/3 of the surviving cases, rebleeding may occur. The risk of re-rupture of intracranial aneurysm is greatest within 2 weeks after rupture. Diagnosis Cerebral angiography is the most accurate method of diagnosis, and whole brain angiography should be performed to understand the location of aneurysm and whether it is multiple. The key to the treatment of subarachnoid hemorrhage is to avoid rebleeding and to prevent vasospasm and its secondary cerebral infarction. The risk of re-rupture and cerebral vasospasm is greatest within 3 weeks after aneurysm rupture. Therefore, patients who are conscious, have no symptoms of focal cerebral deficit and have been stable for one or two days, as well as those who had mild consciousness or focal cerebral symptoms and are starting to improve, should be operated early and promptly if there are no signs of cerebral vasospasm. In recent years, the trend has been to operate within one to three days after the onset of the disease, especially in mild to moderate patients. Patients in lethargy and deep coma are not suitable for surgery in the acute phase, unless the development of intracranial hematoma is life-threatening. 1.Surgical clamping: It is a surgical method to deal with aneurysm directly by opening the skull, which was invented by Walter Dandy in 1937. A special aneurysm clamp is used to close the neck of the aneurysm and to protect the patency of the aneurysm-carrying artery. Today’s aneurysm clips are usually made of titanium and hundreds of different sizes, shapes and models of aneurysm clips have become available, with the appropriate clip chosen according to the size and location of the aneurysm. If the base of the aneurysm is too large or shuttle-shaped to be clamped and its collateral circulation is good, the aneurysm-carrying artery can be ligated and aneurysm isolation performed, or the aneurysm wall can be reinforced by using only muscle sheets and bioadhesive. With the invention of the operating microscope, the development of microsurgery techniques and the use of new aneurysm clips, clamping has gradually become the standard treatment for aneurysms, although it is still an invasive and technically complex procedure. 2. Endovascular intervention: It is a minimally invasive operation that reaches the site to be treated through an endovascular route. In the treatment of cerebral aneurysms, this operation is called spring-ring embolization. Unlike surgery, spring coil embolization does not require opening the skull. Instead, the physician uses real-time x-ray technology (also called fluoroscopic imaging) to visualize the patient’s vascular system and treat the disease located within the vessels. A small incision is made in the groin, a catheter is inserted into the femoral artery, and a tiny platinum spring coil is inserted through the catheter into the lumen of the cerebral aneurysm, blocking the blood flow inside the aneurysm and gradually forming a blood clot to block the aneurysm lumen to reduce the chance of aneurysm rupture. Thousands of patients worldwide have undergone this treatment. Endovascular intervention is effective, less invasive, less complications, no craniotomy and fast recovery, so its application is becoming more and more popular. 3.Complications: Clamping and embolization have some common complications. Aneurysm rupture is one of the most serious complications, and the exact incidence is not clear, but it is estimated to be around 2%-3%. Rupture is capable of causing massive brain hemorrhage, coma, and even death. However, bleeding can be quickly controlled during surgical clamping, when the ruptured aneurysm and the supplying artery can be directly visualized. Ischemic stroke is another common and serious complication, and the type and extent of stroke that can occur is determined by the location and treatment of the aneurysm.