Intracranial aneurysm is a localized abnormal expansion or dilatation of intracranial artery wall, 80% of which occurs in the anterior half of Willis artery ring at the base of the brain, and it is the most common cause of subarachnoid hemorrhage. According to the size of aneurysm diameter, it is categorized as: small aneurysm of less than 0.5cm; aneurysm of equal to or greater than 0.5cm and less than 1.5cm is general aneurysm; aneurysm of equal to or greater than 1.5cm and less than 2.5cm is large aneurysm; aneurysm of equal to or greater than 2.5cm is giant aneurysm. Large aneurysm is equal to or greater than 2.5cm, and giant aneurysm is equal to or greater than 2.5cm, and the most common age is 40-60 years old. Diagnostic basis: 1. When taking medical history, attention should be paid to the patient’s age of onset, whether there are clear triggers, such as defecation, emotional excitement, etc., and whether the patient has cerebrovascular malformations, polycystic kidneys and other congenital diseases, whether there is nosebleed, whether there is a family history of diabetes mellitus, hypertension and arteriosclerosis, and whether there is a history of infection and trauma. 2.Signs and symptoms of unruptured aneurysm: common focal signs caused by aneurysm compression of nerves are: cavernous sinus syndrome (cavernous sinus internal carotid aneurysm), motor nerve palsy (posterior communicating artery aneurysm, anterior choroidal artery aneurysm and aneurysm of the posterior cerebral artery P1 segment, the former is the most common), abducens nerve paralysis, especially bilateral paralysis (basilar artery aneurysm), the more massive anterior half of the loop of Willis artery, the anterior portion of the loop of Willis artery. Aneurysms of the anterior half of the Willis artery ring can cause visual dysfunction (internal carotid artery-ocular aneurysm, anterior cerebral artery horizontal segment aneurysm and anterior communicating artery aneurysm), pituitary gland and hypothalamus dysfunction, and even intracranial hypertension and hemiplegic aphasia, etc. Aneurysms of the posterior half of the Willis artery ring can cause dizziness and tinnitus, cerebellar and brainstem signs. 3.Aura symptoms and signs before aneurysm rupture: some intracranial aneurysm rupture and hemorrhage may have aura manifestations, such as visual field defect with localization significance caused by local expansion, extraocular muscle paralysis, local headache and facial pain, etc., total headache, nausea, neck and back pain, drowsiness, photophobia, etc., and motor and sensory disorders, equilibrium disorders, vertigo, hallucinations, etc., caused by cerebral ischemia. 4. Clinical manifestations caused by rupture and hemorrhage are often the first symptom of intracranial aneurysm, which manifests as sudden onset of disease, severe headache, nausea, vomiting, often combined with different degrees of consciousness disorder, and may be due to the complication of acute hydrocephalus and increased intracranial pressure, and then aggravate the condition due to secondary cerebral vasospasm or worsen the condition and even die due to rebleeding after 4 to 7 days. For specific clinical manifestations and grading, see the chapter of subarachnoid hemorrhage. 5.Diagnosis of rebleedingRebleeding mostly occurs in the recent past of the previous SAH, especially within the first 24 hours, the incidence rate is about 4%, to 2 weeks when the cumulative about 20%, mortality rate of 20% to 50%. About 2 weeks after the first hemorrhage, the patient’s condition improves and then suddenly worsens, severe headache, coma, meningeal irritation signs, lumbar puncture found that the cerebrospinal fluid and fresh blood, or CT, MRI examination of the cerebral pool, ventricles, the subarachnoid space and fresh hemorrhage, etc. are the basis for the diagnosis of re-bleeding. 6.CT scan can determine whether there is subarachnoid hemorrhage, intracerebral hematoma, its hemorrhage range, hematoma size and whether there is secondary cerebral infarction, hydrocephalus and so on. The location of hemorrhage can help to locate the position of aneurysm. For example, anterior traffic aneurysm has more blood accumulation in the suprasellar pool; posterior traffic aneurysm and aneurysm of lateral fissure segment of middle cerebral artery have more blood accumulation in the lateral fissure pool, and some of them are accompanied by hematoma.CT scan can detect huge aneurysm and its occupying effect, but its specificity and sensitivity are not as good as that of MRI and it is not as good as that of MRI in displaying all the aneurysms and their adjacent structures.7. MRI scan shows black hollow image of the intracerebral flow in the cavity of aneurysm in the T2 image, and it shows black hollow image in the T2 image. In T2 image, the blood flow in the aneurysm cavity shows black hollow shadow, and the thrombus in the aneurysm cavity shows white high signal shadow in T1 image, which is obvious in contrast with the surrounding cerebrospinal fluid, and it helps to show the diagnosis of the suspected cases with negative angiography and no hemorrhage or hemorrhage is basically absorbed. 8.DSA is the standard classic examination for diagnosing intracranial aneurysm, except for the condition of Hunt and Hess grade V, angiography should be performed as early as possible. In addition to shooting front and side view film, oblique view film or skull base view film should be taken if necessary, so as to show the aneurysm neck and aneurysm-carrying artery more clearly. Matas test during angiography can help to judge the opening of anterior and posterior communicating arteries, which can be used as a reference for whether the carotid artery or vertebral artery can be temporarily or permanently blocked during the operation. 9. The specificity and sensitivity of CTA for the diagnosis of intracranial aneurysm is close to or reaches the level of DSA. Its superiority over DSA lies in that it can not only show the three-dimensional structure of aneurysm body, neck and cavity, but also show the three-dimensional anatomical relationship between the aneurysm-carrying artery and the peripheral vascular branches, especially when the blood vessels caused by huge aneurysm are displaced or covered by the anterior bed protrusion, which can be shown more clearly. Differential diagnosis Cases of aneurysm rupture and bleeding, especially the local formation of hematoma, which is mostly located in the frontal lobe, ventricles, corpus callosum, septum pellucidum, medial temporal lobe, lateral fissure, and external capsule, etc., should be considered to differentiate from hypertensive cerebral hemorrhage (basal ganglia and thalamus), cerebrovascular malformations and hemorrhage of anomalous vascular reticulation of the base of the brain, cranial cerebral injuries, and hemorrhage of intracranial tumors. Giant intracranial aneurysms can sometimes be misdiagnosed as meningiomas, brain abscesses, substantial craniopharyngiomas or pituitary tumors, etc., which should be differentiated with clinical manifestations or other examination methods.