Approach

Patients with an unruptured cerebral aneurysm may be asymptomatic. As the aneurysm increases in size it may cause symptoms of increased intracranial pressure (such as headaches and vomiting) or focal cranial nerve lesions. Rupture of a cerebral aneurysm with resulting subarachnoid hemorrhage (SAH) is the most feared clinical manifestation of cerebral aneurysms.

History

Unruptured aneurysms are often asymptomatic and are usually detected either incidentally or on screening.[18] Aneurysms can rupture at any time, but rupture may be associated with exertion or stress.[19] An unusual, unexpected abrupt-onset headache is the most common symptom of an aneurysmal subarachnoid hemorrhage and may be accompanied by other symptoms including nausea and/or vomiting, and possibly an abrupt change in consciousness.[19][20]​​[21]​​​​​​ Patients sometimes report an unusual headache several weeks prior, which may represent a minor leak of blood into the wall of the aneurysm or into the subarachnoid space (known as a sentinel headache).[20]​​[22] In some cases the severity of the headache can be quite mild and misleading. Speed of onset may be as significant as severity, and in every patient complaining of a new headache SAH should be considered as an important secondary cause and be investigated when appropriate.[23]​​

Physical examination

In an unruptured aneurysm, the examination is usually unremarkable. However, a pressure effect from the aneurysm may produce focal neurological signs.[24] The classic syndrome is that of a third nerve palsy with pupillary dysfunction from a posterior communicating artery aneurysm exerting mass effect.[18] In a ruptured aneurysm, findings depend on the severity and location of the SAH; there may be nuchal rigidity and intraocular hemorrhage. The neurological exam may be normal in an SAH, show focal neurological signs due to a local mass effect from a hematoma, or the patient may be in a deep coma with decerebrate rigidity.

Investigations

Computed tomography (CT) head without contrast is the preferred initial diagnostic test when SAH is suspected.[20][21]​​​ Modern CT scanners are highly sensitive (92.9%) and specific (100%) for identifying patients with SAH, particularly if performed within 6 hours when sensitivity improves to 97% to 100%.[25] It is reasonable to exclude SAH if a scan performed within 6 hours does not show subarachnoid blood.[20]​ If there is high clinical suspicion for SAH but the CT scan was performed after 6 hours, a lumbar puncture should be performed.[20][21]​​​​ Grossly bloody cerebrospinal fluid (CSF) that does not clear suggests SAH. A more definitive finding is the presence of xanthochromia, a yellowish discoloration of CSF caused by breakdown products of hemoglobin. This usually takes about 12 hours to develop.[26]

Cerebral angiography (conventional catheter-based digital subtraction angiography, CT angiography [CTA], or magnetic resonance angiography [MRA]) is used to delineate the causative aneurysm and direct appropriate definitive management.

​Conventional cerebral angiography is still the preferred imaging modality for a cerebral aneurysm, ruptured or unruptured.[18][20]​​​[27] With a resolution of 50 micrometers, conventional cerebral angiography, including 3-dimensional reconstructions, not only has the highest sensitivity but also allows for better characterization of the morphology, orientation, neck size, adjacent vessels, and any additional aneurysms.

​Both CTA and MRA demonstrate high specificity in detecting aneurysms >3 mm.​[27][28][29]​​​​ CTA can be useful in acute situations because it can be obtained quickly and help guide the decision making and urgency of subsequent studies. MRA takes longer to perform than CTA and is therefore less appropriate for critically ill patients.[29]​ MRA does not carry the risk of ionizing radiation and can be obtained without contrast using time of flight techniques (MRA-TOF). MRA is preferred for screening and serially monitoring unruptured aneurysms. Both CTA and MRA are limited in identifying features and morphology of small (<3 mm aneurysms), and are susceptible to prominent artifacts from prior aneurysm treatments (metallic clips, coils, stents).[Figure caption and citation for the preceding image starts]: Cerebral angiogram showing aneurysmFrom the personal collection of Dr M. Chen, Columbia College of Physicians and Surgeons [Citation ends].com.bmj.content.model.Caption@21a8bee[Figure caption and citation for the preceding image starts]: Comparison of 2-dimensional catheter angiography (left) with 3-dimensional catheter angiography (right) showing a basilar tip aneurysmFrom: Sellar M. Practical Neurology. 2005;5:28-37. Used with permission [Citation ends].com.bmj.content.model.Caption@5b1c9064[Figure caption and citation for the preceding image starts]: Three-dimensional catheter angiogram showing a basilar tip aneurysmFrom: Sellar M. Practical Neurology. 2005;5:28-37. Used with permission [Citation ends].com.bmj.content.model.Caption@57051455

Emerging investigations

MRA vessel wall imaging (VWI) is an emerging tool for the risk stratification of aneurysms, utilizing contrast and high resolution to observe enhancement within the wall of the artery, which may imply instability or inflammation.[30]​ Lack of enhancement has been shown to be strongly predictive of aneurysm stability, but positive enhancement is poorly predictive of instability and many enhancing aneurysms are also stable.[31][32]​ ​Multiple limitations including lack of standardized protocols, variation in the definition of aneurysmal enhancement, and the need for experienced neuroradiologists to interpret the study prevent widespread use, and further validation is required.

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