Circle of Willis with the most common locations of ruptured aneurysms marked Most cases of SAH are due to trauma such as a blow to the head. Traumatic SAH usually occurs near the site of a skull fracture or intracerebral contusion. It often happens in the setting of other forms of traumatic brain injury. In these cases prognosis is poorer; however, it is unclear if this is a direct result of the SAH or whether the presence of subarachnoid blood is simply an indicator of a more severe head injury. In 85 percent of spontaneous cases the cause is a cerebral aneurysm—a weakness in the wall of one of the<unk> es in the brain that becomes enlarged. They tend to be located in the circle of Willis and its branches. While most cases are due to bleeding from small aneurysms, larger aneurysms (which are less common) are more likely to rupture. Aspirin also appears to increase the risk. In 15–20 percent of cases of spontaneous SAH, no aneurysm is detected on the first angiogram. About half of these are attributed to non-aneurysmal perimesencephalic hemorrhage, in which the blood is limited to the subarachnoid spaces around the midbrain (i.e. mesencephalon). In these, the origin of the blood is uncertain. The remainder are due to other disorders affecting the blood vessels (such as cerebral<unk> ovenous malformations), disorders of the blood vessels in the spinal cord, and bleeding into various tumors. Cocaine abuse and sickle cell anemia (usually in children) and, rarely, anticoagulant therapy, problems with blood clotting and pituitary apoplexy can also result in SAH.<unk>  of the vertebral<unk> , usually caused by trauma, can lead to subarachnoid hemorrhage if the<unk>  involves the part of the vessel inside the skull.
complications of Vertebral artery dissection
medical cause of Vertebral artery dissection
symptoms of Vertebral artery dissection
symptom of Vertebral artery dissection
complications of Giant cell arteritis
symptom of Idiopathic intracranial hypertension
complications of Trigeminal neuralgia
symptom of Giant cell arteritis