Diagnosis To determine the presence of subarachnoid hemorrhage (SAH) In the acute phase of hemorrhage, the positive rate of CT to confirm SAH is extremely high, safe, rapid and reliable. Elevated lumbar puncture pressure with bloody cerebrospinal fluid is often direct evidence for the diagnosis of subarachnoid hemorrhage after aneurysm rupture. However, lumbar puncture should be performed with caution when intracranial pressure is very high. Determining the cause and site of lesion Cerebral angiography is the “gold standard” for the diagnosis of intracranial aneurysm, which can clearly determine the site, shape, size, number, presence of vasospasm and the final surgical plan. CTA can replace cerebral angiography to a certain extent and provide more information for the decision of aneurysm treatment. Differential diagnosis Patients with spontaneous subarachnoid hemorrhage In addition to ruptured intracranial aneurysms, cerebral arteriovenous malformations, dural arteriovenous fistulas, cavernous hemangiomas, smoker’s disease, and spinal vascular malformations can also cause spontaneous subarachnoid hemorrhage. Cerebral angiography and CT or MRI of the skull are able to make a definitive diagnosis of the corresponding disease. MRI is an important differentiator, as the signal of the aneurysm cavity is significantly different from that of other tumors, while the thrombotic T1 high signal and iron-containing hemoglobin deposition are also more important. The thrombotic T1 high signal and iron-containing heme deposits are also more characteristic.