Aneurysms

There is a common misconception in people that having an aneurysm means bleeding in the brain. An aneurysm is in fact a balloon-like swelling in a blood vessel that can affect any large vessel in your body; these larger vessels being arteries. Aneurysms pose a risk to health from the potential for rupture, clotting, or dissecting. It is the pressure of the blood passing through a weak part of the blood vessel that forces it to bulge outwards, forming a sort of a blister. If the sac that is formed extends the artery too far, the vessel may burst, causing death by bleeding. Rupture of an aneurysm in the brain causes stroke, and rupture of an aneurysm in the abdomen causes shock. (THIJ, 2001) Aneurysms are the cause of many deaths because they are usually silent until a medical emergency occurs. “One author has referred to an AAA as a "U-boat" in the belly, because they are silent, deep, deadly, and detectable by sound waves.” (Tilson) It is extremely difficult to diagnose an aneurysm. Having a thin body and a moderately large sized aneurysm is the ideal conditions in which you or your doctor may be able to detect one. Most of the aneurysms are discovered as a result of medical imaging for other conditions, by ultrasound exams, CAT scans, MRI's, or even plain X-rays of the abdomen. Aneurysms are also detected by physical exam, on a basic chest or stomach X ray, or by using ultrasound. The size and location can be found through echocardiography or radiological imaging, such as arteriography, magnetic resonance imaging (MRI), and computed topography (CT) scanning. It is very hard to detect aneurysms as their symptoms are not provocative. “Abdominal aortic aneurysms may cause pain or tenderness below your stomach, make you less hungry, or give you an upset stomach. Cerebral (brain) aneurysms may have no symptoms, although you may have headaches, pain in your neck and face, or trouble seeing and talking.” (THIJ, 2001) The treatment of aneurysms depends on the size and location of the aneurysm and the overall health of the patient. “The aneurysms in the upper chest, the ascending aorta are usually operated on right away. Aneurysms in the lower chest and the area below your stomach, the descending and abdominal parts of the aorta may not be as life-threatening.” (THIJ, 2001) “Most nontraumatic subarachnoid hemorrhages are caused by intracranial saccular (berry) aneurysms. An aneurysm is a pathologic widening of the arterial lumen. The major types of intracranial aneurysms are (1) dissecting aneurysms, which are rare and usually involve the extracranial arteries; (2) mycotic aneurysms, which are usually due to bacterial infection; (3) fusiform aneurysms, which are the result of atherosclerosis and are located in the vertebrobasilar and internal carotid artery systems; and (4) saccular aneurysms, which will be the emphasis of this review. (Petito, 1993) Saccular aneurysms that are unrelated to arterial bifurcations make up the minority of aneurysms in this group and are nearly always associated with atherosclerosis. The majorities of saccular aneurysms arise at arterial bifurcations in the subarachnoid space and are known as berry aneurysms. (Stehbens, 1995) “According to autopsy data, an estimated 5 million individuals in North America have intracranial aneurysms, and 28,000 of them rupture annually.4 At the University of Louisville School of Medicine, incidental berry aneurysms have been found in 2% of the autopsy population. Elsewhere, the reported incidence has been between 0.2% and 9.0%, with wide variations attributed to differences among populations and quality of reporting.4 Asymptomatic aneurysms are much more common than symptomatic lesions, making up 95% of the total.5 Berry aneurysms are multiple in 20% to 30% of cases.” (Minyard et al) One non-invasive treatment technique for cerebrovascular is by the optimization of stents using computational fluid dynamics, CFD. “The morphology of the aneurysm and pulsatile flow conditions are determinant factors in aneurysm growth which may lead to rupture with high mortality and morbidity. This study investigates the changes of flow patterns in an experimental 2-D, computational 2-D and 3-D side wall aneurysm model before and after placement of a stent in the parent vessel traversing the ostium of the aneurysm. Implantation of a stent, which covers the aneurysmal ostium, alters local hemodynamics. By reducing the flow into the aneurysm a thrombo-occlusion of the aneurysmal pouch can be achieved. Furthermore, stents induce endothelialization of the stented vessel lumen, however, stent mechanical properties, geometry, and local hemodynamics determine the long term biocompatibility and patency of the implant.” (Lieber, et al) References: Lieber, B.B, and Wakhloo, A.K. (1996) Optimization of Stents for cerebrovascular disorders using Computational Fluid Dynamics and Particle Image Velocimetry. http://www.mae.buffalo.edu/research/summaries/1996/ (Accessed April 7, 2002) Minyard. Andrea N, MD, and Parker, Joseph C. JR., MD, (1997) Intracranial Saccular (Berry) Aneurysm: A Brief Overview. http://www.sma.org/smj/97july2.htm, Louisville, Ky. (Accessed April 7, 2002) Petito CK (1993) Cerebrovascular diseases. Principles and Practice of Neuropathology. St. Louis, Mosby-Year Book Inc, pp 436-458 Stehbens WE (1995) Aneurysms. Vascular Pathology. London, Chapman and Hall Medical, pp 379-400 Tilson, M. David, MD Professor of Surgery Columbia University, http://www.columbia.edu/~mdt1/faqs.html, (Accessed April 7, 2002) Texas Heart Institute Journal, http://www.tmc.edu/thi/aneurysm.html, © Copyright 1996-2002 Texas Heart Institute. (Accessed April 7, 2002)