Subarachnoid hemorrhage (SAH) accounts for nearly 50% of cases of intracranial hemorrhage. Its incidence increases with age, and it is more common in women. African American and Hispanic individuals have a higher incidence of SAH when compared with white individuals. Most SAHs result from saccular, or “berry,” aneurysms. Only a minority of cases of SAH are nonaneurysmal in etiology. Approximately 85% of congenital saccular, or “berry,” aneurysms develop in the anterior part of the circle of Willis. The origin of the posterior communicating artery from the internal carotid artery is the most common site. Such an aneurysm typically presents with headache and third cranial nerve palsy involving the pupil. Vascular malformations within and on the surface of the brain parenchyma constitute approximately 7% of cases of subarachnoid hemorrhage and arise from capillary telangiectasias, cavernous hemangiomas, venous angiomas, or AVMs.
Capillary telangiectasias and both types of angiomas typically have a low bleeding risk (<0.5%/year). Findings that suggest an AVM as the cause of subarachnoid hemorrhage include a history of previous focal seizures, slow stepwise progression of focal neurologic signs, and, occasionally, recurrent unilateral throbbing headache resembling migraine. A bruit may be present over the orbit or skull in approximately 40% of patients. SAH usually presents with abrupt onset severe headache that is typically described by patients as the “worst headache of my life.” The headache occurs in 97% of cases; 30% have symptoms lateralized to the side of the hemorrhage. The combination of vitreous hemorrhage and subarachnoid hemorrhage (Terson syndrome) portends a worse prognosis. Maintaining a high index of suspicion and evaluating the patient with noncontrast CT, followed by mandatory lumbar puncture if CT results are negative, are essential in making the diagnosis. Digital subtraction angiography is superior to CT or MRA for the detection of SAH due to aneurysm.
Prognosis and treatment
Aneurysmal SAH carries a high mortality rate; 10% of individuals with an aneurysmal SAH die before they reach the hospital, 25% die within 24 hours, and 45% within 30 days. Prognostic factors include the patient’s level of consciousness and neurologic grade on hospital admission, the patient’s age, and the amount of blood hemorrhaged, as discovered via the initial head CT. Initial clinical severity may be assessed by a validated scale such as the Hunt and Hess scale because it is the most useful indicator of outcome after acute subarachnoid hemorrhage.
Control and maintenance of BP are mandatory in the treatment of ruptured aneurysms. Surgical intervention is ideally accomplished within 24–72 hours because the likelihood of early rebleeding is high and is associated with a poor outcome. The 2 traditional methods of interventional management are (1) placing a small clip or ligature (clipping) across the neck of the sac and (2) endovascular coiling. If an aneurysm is judged to be suitable for either technique, results of an analysis of 3 randomized trials favor endovascular coiling over clipping in the surgical management of intracranial aneurysms. Patients with large intraparenchymal hematomas or middle cerebral artery aneurysms may have better outcomes with clipping. Complete obliteration of the aneurysm is recommended, and patients who undergo either surgical intervention should undergo immediate angiography after the surgery to identify any remnants that may require retreatment. If the aneurysm cannot be directly obliterated, surgical ligation of a proximal vessel may be necessary. Complex aneurysms can also be treated with flow-diverting stents, which shunt blood flow from the aneurysmal vessel, thereby activating the coagulation cascade to stimulate gradual thrombosis of the aneurysm. Flow-diverting stents may result in a paradigm shift in treatment of aneurysms usually treated by traditional endovascular or microsurgical intervention, but long-term comparative data are not yet available.
The current gold standard of treatment is the surgical excision of a symptomatic AVM. Stereotactic radiosurgery and hypofractionated stereotactic radiotherapy are valuable treatment options in patients with symptomatic AVMs deemed at a high risk for surgical excision; these methods are associated with low morbidity and mortality, with good occlusion rate. At present, medical therapy is preferred over surgery in patients with unruptured AVMs.
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Lu L, Zhang LJ, Poon CS, et al. Digital subtraction CT angiography for detection of intracranial aneurysms: comparison with three-dimensional digital subtraction angiography. Radiology. 2012;262(2):605–612.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.