Aneurysms develop at sites of developmental defects in the media and elastica of the cerebral arteries. Often they are multiloculated and sometimes, multiple. These are called berry aneurysms. They are usually located at bifurcations and branching of the vessels. Approximately 90% of the aneurysms are located on the anterior part of the circle of Willis. The common sites include the anterior communicating artery, origin of the posterior communicating artery (PCA), major bifurcations of the MCA, and the bifurcation of the ICA into MCA and ACA. Other sites include ICA in the cavernous sinus and bifurcation of the basilar artery. Many of them remain silent during life and may be detected at autopsy. Others may rupture giving rise to intracranial bleeding.
Before rupture: Most of the aneurysms are asymptomatic until they rupture. They may however, become symptomatic by causing pressure on the adjacent structures. A large aneurysms of the ICA may produce compression of the optic chiasma, third, fourth and sixth nerves, and Ophthalmic division of the fifth cranial nerve. Posterior communicating artery aneurysms produce pressure on the ipsilateral third nerve.
After rupture: Rupture of an aneurysm results in subarachnoid hemorrhage. The patient usually presents with excrutiating headache of sudden onset followed by loss of consciousness. Sometimes consciousness is lost without any premonitory symptoms. Rarely, the leak is small and only mild headache may develop without further progression. The sensorium may improve within a few hours but usually confusion lasts for ten days or more. In many cases, lateralizing signs may not be present. These signs help to localize the aneurysm in those cases with focal neurological deificits. Signs of meningeal irritation like neck rigidity. Kernig’s sign and Brudzinski’s signs are usually present. Examination of the fundus frequently reveals pre-retinal or subhyaloid hemorrhages. In those with raised intracranial tension papilledema may develop.
Subarachnoid hemorrhage should be suspected when an otherwise healthy individual suddenly develops severe headache associated with features of meningeal irritation without fever or other signs of infection. Lumbar puncture (LP) confirms the clinical diagnosis. Examination of the CSF is diagnostic. It is under pressure and is uniformly blood-stained. When the CSF is centrifuged, the supernatant is xanthochromic (yellow colored) if the LP is done at least 12 hours after the bleed. The yellow color is due to break down of hemoglobin and formation of bilirubin. Sometimes CSF may be blood stained due to bleeding from veins injured during the LP (traumatic bleeding). In this case the CSF clears up as it flows. On standing, traumatic blood clots whereas subarachnoid bleeding is not xanthochromic. Lumbar puncture is a dangerous procedure in patients with raised intracranial tension. Since CT scan is a very reliable non-invasive method to locate subarachnoid bleeding, it should be done as the first investigation wherever facilities are available.
The CT scan picks up the subarachnoid blood and sometimes the ruptured aneurysm in the first few days, and this is the most accepted noninvasive method to demonstrate them. The direct method to visualize aneurysm is carotid or vertebral angiography. In many cases of the aneurysms are seen. Sometimes, the site of the aneurysm may seal off and the sac may be thrombosed so that angiogram may be negative.
Course: Aneurysm bleed tends to recur after a period of initial hemostasis. This risk is maximum in the first 2 weeks after which the incidence of re-bleed gradually comes down. Mortality is high in spontaneous subarachnoid hemorrhage. Initial mortality is 20-25%. Recurrence of bleeding increases the mortality further.
Management: Definitive treatment of the aneurysm is surgical. Once subarachnoid hemorrhage is diagnosed and aneurysm identified by angiography, the next step is to decide the time of surgery. In deeply comatose patients, surgery carries a high risk. Hence it is better to operate when the patient’s general condition has improved. General management in such instances consists of absolute bed rest, continuous sedation, and control of hypertension and seizures if present. Liquid paraffin 10 ml may be given twice daily to keep feces soft and avoid straining. Administration of the antifibrinolytic agent epsion-amino caproic acid (EACA) in an hourly dose of 1g given orally or through a nasogastric tube for the first 3 weeks to the time of operation has been found to reduce the risk of re-bleed. The adverse side effect is extensive thrombosis. Once the general condition is stabilized, surgical ligation of the aneurysm is advised to prevent recurrence of bleeding. Other surgical procedures include clipping the aneurysm, occluding the aneurysms, and favoring thrombosis by embolization or strengthening the sac by fascial is not possible, ipsilateral carotid ligation may be necessary after confirming the patency of the opposite carotid artery.