Brain Aneurysms - Epidemiology and Risk Factors - Essay Example

Brain Aneurysms Introduction Abnormal localized dilatation of a blood vessel is known as aneurysm (Biousse and Newman, 1999). When a vessel of the brain is affected by such dilatation, it is termed as brain aneurysm or intracranial aneurysm. Intracranial aneurysms are common and can occur in 3.5% to 6% of population. They go unnoticed until they rupture (Vega, Kwoon and Lavine, 2002). Ruptured aneurysms are associated with high mortality and morbidity. 10-20 percent of patients with ruptured aneurysm die before they reach the hospital and 8 percent of survivors die due to progressive deterioration (Vinas and Wilner, 2008). Without proper treatment, patients with ruptured aneurysms have limited functional survival. It has been estimated that only 18 percent are functional survivors at 10 years and 8 percent are disabled, the rest die (Vinas and Wilner, 2008). Thus, it can be said that aneurysms of brain have potential to cause death, debility and deformity. Epidemiology and risk factors The risk factors can be inherited or acquired (Vega et al, 2002). The disease can occur as familial clustering with no other hereditary disease in the family. The cause for this is not yet known. Research has shown that the incidence of brain aneurysms is about 8-9 percent in those with more than one relative suffering from either an aneurysm or subarachnoid hemorrhage (Vega et al, 2002). Also, there are reports that siblings of affected individuals have higher chances of developing subarachnoid hemorrhage due to aneurysms. Thus it can be said that aneurysm has generic and hereditary links. It has been proposed that certain hereditary connective tissue disorders are associated with the development of aneurysms because of weakening of the vascular walls (Vinas and Wilner, 2008). Some research has shown that 10- 15 percent of patients with autosomal dominant condition polycystic kidney disease develop intracranial aneurysms (Vega et al, 2002). However another connective tissue disorder Marfans syndrome which was incriminated in the development of brain aneurysms is no longer found to be associated with aneurysms (Vega et al, 2002). Other conditions which have been reported to be associated with brain aneurysms are fibromuscular dysplasia, coarctation of aorta and pheochromocytoma. It has been thought that the elevated blood pressure in these conditions is the cause for the development of aneurysms. Other inherited risk factors which have been incriminated in the development of aneurysms include alpha-glucosidase deficiency, Noonans syndrome, tuberous sclerosis, Klineflters syndrome, alpha-1 antitrypsin deficiency, neurofibromatosis type-1, hereditary hemorrhagic telangiectasia, pseudoxanthoma elasticum and type-IV Ehlers-Danlos syndrome (Vega et al, 2002). Other non-heritable risk factors include female gender, advanced age (beyond 50 years of age), cocaine abuse, head injury, current cigarette smoking, infection of the vessel wall, alcohol, hypertension, oral contraceptive use, hypercholesterolemia and intracranial neoplasm or metastases (Vega et al, 2002). Cocaine causes weakening and inflammation of arterial walls (Wedro and Stoppler, 2009). Pathophysiology Aneurysms can affect anterior circulation or the vertebrobasilar or posterior circulation. The anterior circulation aneurysms arise from the internal carotid artery or its branches and the posterior circulation aneurysms arise from basilar artery, vertebral artery or their branches (Vinas and Wilner, 2008) Brain aneurysms may be classified into fusiform, saccular and dissecting types. Most of the aneurysms are saccular or berry type aneurysms. Infact, most of the subarachnoid hemorrhages occur due to them. These aneurysms arise due to defects in the tunica muscularis of the arteries (Biousse and Newman, 1999). It has been proposed that alterations of the lamina elastica interna of the cerebral arteries weaken the walls of the vessel and make them less resistant to various changes in the intraluminal pressure, thus causing dilatation and aneurysm (Vinas and Wilner, 2008). Current research has pointed to mural degeneration as the most important pathogenetic factor for aneurysmal formation (Vinas and Wilner, 2008). Most often than not, the changes occur at sites of vessel bifurcation where turbulence of blood flow is high and the arterial wall shear forces are greatest (Vega et al, 2002). While saccular aneurysms are most frequently seen in the first and second order arteries originating from the circle of Willis which is present at the base of the brain, fusiform aneurysms arise from tortuous, ectatic cerebral arteries from the vertebrobasilar arteries. These dilatations can be large and have a diameter of several centimeters (Vinas and Wilner, 2008). These aneurysms usually do not result in subarchnoid heamorrhage, rather, the mode of presentation would be compression of the cranial nerves or brainstem. Dissecting aneurysms occur either due to trauma to the artery or due to cystic medial necrosis of the artery. They form a false lumen through which the blood traverses and the true lumen collapses (Vega et al, 2002). Clinical presentation Most of the brain aneurysms are asymptomatic and detected only when imaging is done for some other purpose or their rupture has caused clinical symptomatology. The most common clinical presentation is subarachnoid hemorrhage which is a medical emergency. The typical presentation of subarachnoid hemorrhage is severe atypical headache which the patient describes as the worst headache. The headache may be associated with other symptoms like nausea, vomiting, loss of consciousness, meningismus and focal neurologic deficits. The presentation of subarachnoid hemorrhage is very typical. But despite, this, the condition goes undiagnosed in many people in the initial stages. Infact, in 50 percent of the people, the initial symptoms are milder due to small leak prior to full rupture of the artery (Vega et al, 2002). Unruptured aneurysms may also present with some acute and chronic symptoms. Some of the acute symptoms which have been reported are severe headache, transient ischemia, seizures, oculomotor nerve palsy and seizures. The chronic symptoms are chronic vision loss, noncatastrophic headache of different character, chronic loss of vision, unilateral optic neuropathy, facial pain and motor neuropathy not involving eye. Aneurysms which are large and located in the posterior circulation are more likely to present with symptoms even in unruptured stage (Vega et al, 2002). Diagnosis The most definitive diagnostic test is imaging (Vega et al, 2002). There are several different imaging techniques which are useful like computed tomographic angiography, intra-arterial digital subtraction angiography, magnetic resonance angiography and transcranial doppler ultrasonography. While magnetic resonance angiography is 69- 100 percent sensitive and 75- 100 percent specific, computed tomographic angiography is 85-95 percent sensitive (Vega et al, 2002). The sensitivity and specificity of doppler are much lower than others. Of these, the gold standard test is intra arterial digital subtraction test, but it is associated with one percent risk of transient neurologic complications and 0.5 percent risk of permanent neurologic complications. Whenever magnetic resonance imaging is employed in a patient with previous surgery, caution must be exercised because of threat to the patient due to surgical clips (Vega et al, 2002). Differential diagnosis Differential diagnosis of brain aneurysms include meningitis, stroke, tumor and migraine headache (Wedro and Stoppler, 2009). Complications of subarachnoid hemorrhage Patients with aneursymal subarachnoid hemorrhage suffer from serious sequelae which include neurological and cognitive deficits subsequent to primary hemorrhage or due to secondary injury mechanisms. The complications may be either medical or neurologic. Most of the morbid conditions are related to neurologic deficits like aneurysmal rebleeding and vasospasm. Medical complications contribute to significant morbidity and infact are responsible for 23 percent deaths due to aneurysmal subarachnoid hemorrhage. (Vinas and Wilner, 2008) The main medical complications are fluid and electrolyte abnormalities due to inappropriate atrial natriuretic factor secretion. About 35 percent of patients with subarachnoid hemorrhage develop hyponatremia and cerebral salt wasting. Hyponatremia can worsen the level of consciousness and contribute to cerebral edema and seizures. Management of hyponatremia is very tricky and complex. Other medical complications include arrhythmias, pulmonary complications and hypoxia. Neurological complications include vasospasm, rebleeding and hydocephalus. the most serious and disastrous of these is aneurysmal bleeding. The highest frequency of rebleeding occurs on the first day of subarachnoid hemorrhage which is 4 percent. 15-20 percent of patients suffer from rebleeding within 2 weeks time and 50 percent experience it within 6 months time (Vinas and Wilner, 2008). The mortality rates of rebleeding are as high as 70- 90 percent (Vinas and Wilner, 2008). Thus early interventions are essential to eliminate the chances of rebleeding. Acute hydrocephalus is very common with aneurysmal subarachnoid hemorrhage and the incidence during the first 3 days of hemorrhage is about 20 percent (Vinas and Wilner, 2008). 10- 37 percent people who survive sub arachnoid hemorrhage develop chronic hydrocephalus (Vinas and Wilner, 2008). Risk of aneurysmal rupture The annual rupture rates for brain aneurysms are 1.4 to 1.9 percent. The rates are higher for those with diameters larger than 10mm. Also, symptomatic aneurysms and those located in the posterior circulation have higher risk of rupture. There are reports than even small aneurysms have a risk of rupture and hence all patients with intracranial aneurysms must be under vigilant neurosurgical surveillance (Vega et al, 2002). Since rupture of brain aneurysms is associated with high morbidity and mortality, it is important to determine the chances of rupture of an aneurysm for appropriate management (Juvela, Porras and Poussa, 2000). According to the International Study of Unruptured Intracranial Aneurysms or ISUIA (1998; cited in Vega, Kwoon and Lavine, 2002), aneurysms less than 10mm diameter and no history of subarachnoid hemorrhage have 0.05 percent risk of rupture, while, those with similar size but history of subarachnoid hemorrhage have 10 times more risk of rupture (Vega et al, 2002). Treatment Any patient with brain aneurysm must be seen and followed up by a neurosurgeon. Treatment is mainly invasive and instituted only for high risk category. The two main surgeries are open craniotomy and endovascular surgery (Vega et al, 2002). Craniotomy and open repair : In this surgery, the artery is visualized after craniotomy and the site of aneurysm is repaired. The surgery is associated with a mortality rate of 2.6 percent and morbidity rate of 10.9 percent. This surgery is preferred only in those with large aneurysms more than 10 mm because of the high risk associated with the surgery (Vega et al, 2002). Older population have higher morbidity and mortality rates. Endovascular repair: In this repair, custom-made microwires are fitted into the abnormal portion of the vessel occluding it so that rupture is not possible. This procedure is associated with lesser morbidity and mortality rates compared to craniotomy. It is however unclear as to whether the artery must be occluded partially or completely (Vega et al, 2002). Screening for aneurysms in the brain Recent research has pointed to the importance of screening of brain aneurysms because of the potential chances of devastating morbidity and mortality associated with the condition. However, it has been reported that there are no benefits in screening asymptomatic patients with no risk factors. This is because; this category of people have low risk of aneurysms and even if present, the risk of rupture is low. Also, it has been suggested that there is no need to screen patients with acquired risk factors like smoking and alcohol abuse (Vega et al, 2002). There is controversy as to whether patients with family history of ruptured brain aneurysm need screening. Similarly it is still unclear whether those with more than one family member with aneurysm need screening (Vega et al, 2002). Some research has shown that screening does not decrease the morbidity and mortality of aneurysms and thus screening must be decided based on case-to-case basis (Vega et al, 2002). In those with history of aneurysmal subarachnoid hemorrhage, the rate of formation of new aneurysms is 1-2 per year and thus, these patients must be under surveillance with intra-arterial digital subtraction angiography and magnetic resonance angiography (Vega et al, 2002) References Biousse, V., Newman, N.J. (1999). Aneurysms and subarachnoid hemorrhage. Neurosurg Clin N Am., 10(4), 631-51. Juvela, S., Porras, M., Poussa, K. (2000). Natural history of unruptured intracranial aneurysms: probability of and risk factors for aneurysm rupture. J Neurosurg, 93(3), 379-87. Vega, C., Kwoon, J.V., and Lavine, S.D. (2002). Intracranial Aneurysms: Current Evidence and Clinical Practice. American Family Physician. Retrieved on 20th November, 2009 fromhttp://www.aafp.og/afp/20020815/601.html Vinas, F.C., and Wilner, H.I. (2008). Brain, Aneurysm. Emedicine from WebMD. Retrieved on 20th November, 2009 fromhttp://emedicine.medscape.com/article/337027-overview Wedro, B.C. and Stoppler, M.C. (2009). Brain Aneurysm. Medicinet.com. Retrieved on 20th November, 2009 fromhttp://www.medicinenet.com/brain_aneurysm/article.htm Read More