Walsh & Hoyt: General Clinical Manifestations

As recognized by Beadles, aneurysms may cause symptoms in three ways. (a) Large aneurysms can produce symptoms from mass effect, in which case the symptoms depend on the function of the adjacent neural tissue. The frequency of mass effect also depends on the location of the aneurysm. Cavernous sinus aneurysms have a high incidence of locally produced symptoms, whereas distal intradural aneurysms are usually silent, unless they bleed or become large (greater than 25 mm). Focal neurologic symptoms may include cranial nerve palsies, seizures, focal motor weakness or numbness, cognitive impairment, or other cortical or brainstem signs. (b) Aneurysms may alter the distal circulation of their parent vessels or distal branches from those vessels. They may cause vascular compromise (stenosis or thrombosis), distal embolization (artery-artery embolization), or steal phenomena from alterations in the overall hemodynamics of the system, resulting in transient or permanent neurologic deficits. (c) Most frequently, aneurysms cause symptoms when they rupture. Immediate effects include local loss of perfusion pressure and increased ICP that alters cerebral blood flow. Later effects are caused by spasm of the intracranial vessels mediated through exposure to subarachnoid blood and disturbances in CSF dynamics leading to hydrocephalus. Visual system involvement with symptomatic aneurysms is common and may herald aneurysm rupture.