However, smooth muscle cells from the tunica media layer of the artery moved into the tunica intima, where the function of the smooth muscle cells changed from contractile function into pro-inflammatory function. This causes the fibrosis of the arterial wall, with reduction of number of smooth muscle cells, abnormal collagen synthesis, resulting in a thinning of the arterial wall and the formation of aneurysm and rupture. No specific gene loci has been identified to be associated with cerebral aneurysms.Generally, aneurysms larger than 7 mm in diameter should be treated because they are prone for rupture. Meanwhile, aneurysms less than 7 mm arise from the anterior and posterior communicating artery and are more easily ruptured when compared to aneurysms arising from other locations. Saccular aneurysms
Saccular aneurysms are almost always the result of hereditary weaknesses in blood vessels and typically occur within the arteries of the circle of Willis, in order of frequency affecting the following arteries:
Anterior communicating artery
Posterior communicating artery
Middle cerebral artery
Internal carotid artery
Tip of basilar arterySaccular aneurysms tend to have a lack of tunica media and elastic lamina around their dilated locations (congenital), with a wall of sac made up of thickened hyalinized intima and adventitia. In addition, some parts of the brain vasculature are inherently weak—particularly areas along the circle of Willis, where small communicating vessels link the main cerebral vessels. These areas are particularly susceptible to saccular aneurysms. Approximately 25% of patients have multiple aneurysms, predominantly when there is a familial pattern.
The risk of rupture is less than one percent for aneurysms of this size.The prognosis for a ruptured cerebral aneurysm depends on the extent and location of the aneurysm, the persons age, general health, and neurological condition. Some individuals with a ruptured cerebral aneurysm die from the initial bleeding. Other individuals with cerebral aneurysm recover with little or no neurological deficit. The most significant factors in determining outcome are the Hunt and Hess grade, and age. Generally patients with Hunt and Hess grade I and II hemorrhage on admission to the emergency room and patients who are younger within the typical age range of vulnerability can anticipate a good outcome, without death or permanent disability. Older patients and those with poorer Hunt and Hess grades on admission have a poor prognosis. Generally, about two-thirds of patients have a poor outcome, death, or permanent disability.Increased availability and greater access to medical imaging has caused a rising number of asymptomatic, unruptured cerebral aneurysms to be discovered incidentally during medical imaging investigations. This may lead to surgery including endovascular, or simple monitoring. Recently, an increasing number of aneurysm features have been evaluated in their ability to predict aneurysm rupture status, including aneurysm height, aspect ratio, height-to-width ratio, inflow angle, deviations from ideal spherical or elliptical forms, and radiomics morphological features.