Aneurysms- Definition, Types, Causes, Pathogenesis, Clinical Correlations, AAA, ATA, Brain aneurysms

an aneurysm is a localized abnormal permanent dilation of a blood vessel typically an artery or the heart that may be congenital or acquired aneurysms can occur anywhere in the body but more common in the aorta iliac and femoral arteries popliteal artery and cerebral arteries especially in the circle of willis in addition mesenteric splenic and renal arteries are also affected if we recall the structure of a blood vessel it consists of three main layers tunica entema which is the innermost layer tunica media which is the middle layer and tunica adventitia which is the outermost layer tunica entema consists of the endothelium connective tissue and internal elastic lamina tunica media mainly contains smooth muscle cells and tunica adventitia consists of the external elastic lamina connective tissue nerve fibers and blood vessels supplying the tunica media which are known as wasa vasurum aneurysms can be classified as true aneurysms and false or pseudo aneurysms true aneurysms occurring in an artery involve all the three layers of the artery and if it occurs in the heart it involves the full thickness of the heart wall conversely false aneurysms result when there is a defect in the arterial wall that leads to the formation of an extravascular hematoma that communicates with the intravascular space here the hematoma is not surrounded by all the three layers of the artery instead it is covered only by the adventitia of the artery similarly hematomas result from ventricular rupture are covered by the pericardium creating a false aneurysm true aneurysms occurring in arteries can be further divided into two types saccular aneurysms bulge out only on one side of the artery these types of aneurysms are commonly seen in the brain the other type is fusiform aneurysms which bulge out from the artery circumferentially just like a balloon overall few c4 mannerisms are the commonest type now let's discuss about the etiology and pathogenesis of aneurysms atherosclerosis and hypertension are the two most common causes for aneurysms in addition infections such as syphilis and tuberculosis congenital connective tissue disorders like marfan syndrome ehlers-danlos syndrome and lowe's deet syndrome as well as acquired connective tissue abnormalities caused by vitamin c deficiency such as scurvy can also lead to the formation of aneurysms other congenital causes of aneurysms include fibromuscular dysplasia and inherited berry aneurysms of brain in addition vascular trauma and vasculitis can also cause formation of aneurysms now let's see how these eto logic factors lead to aneurysm formation separately atherosclerotic aneurysms are the most common type and they are commonly seen in the abdominal aorta and common iliac arteries atherosclerosis promotes aneurysm formation by three mechanisms atherosclerotic plaques increase the thickness of the vessel wall which impairs the diffusion of oxygen to the tunica media as a result medial ischemia develops followed by medial necrosis and degeneration ultimately the arterial wall becomes weaker which predisposes to aneurysm formation and in an atherosclerotic plaque there is extensive ongoing inflammation so leukocytes secrete proteolytic enzymes such as collagenases and matrix metalloproteinases leading to the destruction of the extracellular matrix which ultimately causes medial necrosis and degeneration and weakening of the vessel wall predisposing to aneurysm formation atherosclerotic plaques also cause direct compression on the tunica media and weakening of the vessel wall aneurysms due to hypertension commonly occur in the thoracic aorta here persistent hypertension causes narrowing of the lumen of waste of vasorum of the aorta this will impair the oxygen supply leading to ischemia to the outer media causing necrosis and degenerative changes followed by weakening of the vessel wall aneurysms due to infections are known as mechatic aneurysms they can originate in three ways from embolization of a septic and bolus usually is a complication of infective endocarditis or as an extension of an adjacent suppurative process or by circulating organisms directly infecting the arterial wall here aneurysm formation is a long-term complication of the infection because infection causes inflammation of the vessel and this will ultimately heal by fibrosis so the arterial wall will become weakened predisposing to aneurysm formation aneurysms commonly occur in the thoracic aorta although it is an infectious cause of aneurysms the pathogenesis of syphilitic aneurysms is a bit different than mechatic aneurysms they commonly occur in tertiary syphilis here the chronic infection involving the waste of vasorum leads to endarteritis obliterans which compromises the blood supply to aortic media causing medial degeneration if we take connective tissue disorders in marfan syndrome there are defects in the extracellular matrix synthesis particularly elliston in ehlers-danlos syndrome there is formation of defective type 3 collagen and loe's deet syndrome defects in transforming growth factor beta leads to formation of defective collagen and in scurvy due to the deficiency of vitamin c which is essential for collagen synthesis there is defective cross-linkage of collagen which leads to weakening of the vessel wall in vascular trauma and vasculitis the initial damage to the vessel is healed by fibrosis which causes weakening of vessel wall predisposing it to aneurysm formation now let's discuss about aneurysms in relation to their location abdominal aortic aneurysms most commonly occur due to atherosclerosis they are usually positioned below the renal arteries and above the aortic bifurcation and saccular or fusiform in shape they are more common in men and smokers older than 50 years most often thrombosis occurs within the aneurysm due to the stasis of blood abdominal aortic aneurysms are asymptomatic most of the time and discovered incidentally on physical examination as a pulsating mass that may mimic a tumor these aneurysms can rupture and bleed into the peritoneal cavity and retroperitoneal tissues they can also compromise the blood flow to the distal organs such as lower limbs compression on the adjacent structures by the aneurysm especially ureters can cause obstructive uropathy and compression on the vertebrae can cause erosions and eventually pathological fractures finally thrombi within the aneurysm can embolize causing ischemic complications in distal organs that have an end arterial supply thoracic aortic aneurysms can occur in the ascending aorta as well as in the descending aorta they occur commonly due to hypertension other causes include connective tissue disorders and syphilis unlike abdominal aortic aneurysms thoracic aortic aneurysms can present with symptoms due to their pressure effects on adjacent structures some of these include breathing and swallowing difficulties persistent cough due to compression of the recurrent laryngeal nerve pain due to erosion of bone valvular insufficiency and heart failure and in conditions where the aneurysm is formed in the root of the aorta rupturing of these aneurysms can cause bleeding into the pericardium resulting in cardiac tamponade and in severe cases rupture of an aneurysm can cause massive bleeding into the mediastinum leading to extremely fatal consequences inherited bury aneurysms of the brain are the commonest type of cerebral aneurysms and they are commonly found in the anterior circulation of the circle of willis they are sacular in shape and rupture of these aneurysms results in bleeding into the subarachnoid space there is another type of aneurysms called charcot bouchard aneurysms which are small micro aneurysms that occur in the small penetrating arteries of the brain hypertension is the most common cause of these aneurysms rupture of these aneurysms can lead to intracerebral hemorrhage cardiac aneurysms are most commonly seen in the ventricles of the heart most common cause of these aneurysms is myocardial infarction because when an area of the myocardium is infected it can no longer contract and ultimately it heals by fibrosis as mentioned throughout this video fibrosis causes weakening of the affected tissue in this case the myocardium this weakening predisposes to the formation of aneurysms you