Aneurysm

Aneurysem[1]

An aneurysm is an abnormal focal arterial dilation. They are classified into true and false aneurysms (pseudo-aneurysm). True aneurysms involve all three layers of the arterial wall. A false aneurysm is a collection of blood which has leaked out of the artery but is then confined next to the vessel by surrounding tissue.

Presentation

Presentation varies with the type of aneurysm involved. Most patients with AAA are asymptomatic but come to medical attention by finding of a pulsatile mass on physical examination, as the result of other abdominal imaging studies, or through ultrasound screening programs for AAA [8]. Patients suffering from cerebral aneurysms may present with headache, nosebleed, visual symptoms, facial pain, altered levels of consciousness which may or may not be accompanied with seizures and autonomic disturbances.

Entire body system
Face, Head & Neck
Eyes

Workup

Laboratory tests

  • Complete blood count
  • Prothrombin time and complete blood profile
  • Serum electrolytes
  • Arterial blood gases
  • Liver function tests

Imaging 

Imaging studies include angiography, CT scan, MRI, Doppler ultrasound and echocardiography. For cerebral aneurysm, imaging tests like transcranial doppler ulrasonography, lumbar puncture and cervical spine imaging may be conducted.

Test results

On the basis of tests and imaging studies, the site of the aneurysm may be localized and often, the underlying cause may also be identified.

Treatment

Medication

Medication include the use of calcium channel blockers, anticonvulsants if needed, and beta blockers. At least one clinical study showed that people who took beta blockers had a slower rate of growth of their AAA compared with people who took a placebo (0.36 versus 0.68 cm per year) [9].

Surgery

Surgical intervention includes insertion of a surgical clip in the neck of the aneurysm. Endovascular coiling of the aneurysm can also be performed, often yielding better results.

Prognosis

It has been suggested that patients with untreated large ascending or descending thoracic aneurysms are more likely to die of complications associated with their aneurysms than from any other cause [6]. Re-rupture, particularly in subarachnoid hemorrhage (SAH) associated with cerebral aneurysm (CA), is associated with a mortality that is estimated to be 70 percent and aneurysm repair is the only effective treatment to prevent this occurrence [7]. Overall, aneurysm is a progressive condition with mortality rates directly proportional to size of the dilation.

Etiology

Aneurysms have many causes. They can be due to congenital diseases, particularly those that damage the connective tissue, such as Marfan syndrome, Ehlers Danlos syndrome or Loeys-Dietz syndrome. Tilson et al described the potential for an autoimmune basis for the development of abdominal aortic aneurysms (AAA) involving the DRB1 major histocompatibility locus [2].

Conditions causing a disbalance in synthesis and degradation of collagen, such as increased matrix metalloproteinase (MMP) production by macrophages, decreased tissue inhibitor of metalloproteinase (TIMP) expression also contribute to aneurysm formation. Lastly, factors based on lifestyle such as hypertension, obesity, atherosclerosis, and high cholesterol, may also lead to the development of aneurysms. Indeed, hypertension and atherosclerosis are the two most important predisposing factors to aneurysms.

Epidemiology

Incidence

The incidence of aneurysms varies depending upon the type and gender. For example, AAA occur 8.2% in males in the UK but females only have an incidence of 0.6-1.4%.

Age

In males the peak age of aneurysms is 80 years but the incidence peaks from 50 years of age. Females have a slightly delayed onset, with incidence rising sharply after the 6th decade of life.

Sex

Aneurysms are more common in males, with an approximate ratio of 2:1. However, the risk of rupture of large aneurysms (≥5.0 cm) is significantly greater in women than men (18 versus 12 percent) [3].

Race

Aneurysms are much more common in Caucasians than people belonging to African-American and other races.

Sex distribution
Age distribution

Pathophysiology

Aneurysms develop due to damage to vessel walls either due to factors acting directly on the vessel walls and weakening them, such as atherosclerotic plaques, nonenzymatic glycosylation of vessels in diabetes mellitus, and hypertension, or due to congenital defects in connective tissue structure and formation. Ischemia also contributes to the pathogenesis. Some common aneurysms are described below:

Abdominal aortic aneurysm

The United States National Lung, Heart and Blood Institute supported a research program that identified the following as mechanisms important in the development of AAA [4]: Proteolytic degradation of aortic wall connective tissue which is followed by inflammation and immune responses. Two other factors include biochemical stress and molecular genetics.

Thoracic aortic aneurysm 

Thoracic aortic aneurysms are most commonly associated with hypertension, although other causes such as Marfan syndrome and Loeys-Dietz syndrome are increasingly recognized [5]. They may encroach on mediastinal structures leading to respiratory distress, difficulty in swallowing due to compression of esophagus, cough and hoarseness of voice due to irritation of recurrent laryngeal nerves, and sometimes secondary cardiac disease.

Prevention

Control and limiting of predisposing factors such as obesity and hypertension are of prime importance in preventive therapy. Particular care should be taken by diabetic patients to keep both blood sugar levels and cholesterol levels in normal limits.

Summary

An aneurysm may be defined as a localized abnormal dilation of a blood vessel or the heart [1]. It can arise anywhere in the body with varying presentations. Aneurysms can be both congenital and acquired. They can be classified on the basis of shape and size of the dilation into 2 main types.

  • Saccular aneurysms are outpouchings of the vessel wall that are spherical and sac-like in shape. Their size ranges from 5-20cm in diameter. They often contain thrombi. On imaging, they appear as lump-like dilations.
  • Fusiform aneurysms are somewhat less dilated in diameter but are longer in length. They are diffuse, circumferential dilations that involve a long vascular segment and appear as longitudinal arc-like swellings on imaging. Lumps are less pronounced. Their diameter may be the same as, or, slightly less than that of saccular aneurysms but they vary greatly in length. Fusiform aneurysms commonly involve extensive areas of the aortic arch and other portions of the vascular channel such as portions of the iliac arteries and parts of the abdominal and thoracic aorta.

Patient Information

Definition

An aneurysm is defined as a segmental, full-thickness dilation of a blood vessel 50 percent greater than its normal diameter [10].

Cause

They can be present from birth or develop later in life due to various reasons such as hypertension, obesity, high cholesterol, diabetes and weakening of vessel wall due to old age.

Signs and symptoms

Most aneurysms are asymptomatic, coming to notice usually during routine examinations. Rupture of an aneurysm, however, is a medical emergency and presents as sharp pain and subsequent collapse. Cerebral aneurysms may preset with symptoms of headache, visual disturbances, seizures and facial pain.

Treatment

Treatment is supportive unless there is a high chance of rupture, in which case surgical intervention is imperative.

Self-assessment

References

  1. Robbins and Cotran, Pathologic Basis of Disease. 8th ed. Pa: Saunders Elsevier. Ch 11 p 506-9, 2010. 
  2. Tilson MD, Ozsvath KJ, Hirose H, Xia S. A genetic basis for autoimmune manifestations in the abdominal aortic aneurysm resides in the MHC class II locus DR-beta-1. Ann N Y Acad Sci. Nov 18 1996;800:208-15. 
  3. Norman PE, Powell JT. Abdominal aortic aneurysm: the prognosis in women is worse than in men. Circulation 2007; 115:2865. 
  4. Wassef M, Baxter BT, Chisholm RL, Dalman RL, Fillinger MF, Heinecke J, et al. Pathogenesis of abdominal aortic aneurysms: a multidisciplinary research program supported by the National Heart, Lung, and Blood Institute. J Vasc Surg. Oct 2001;34(4):730-8.
  5. Homme J et al: Surgical Pathology of the ascending aorta: a clinicopathologic study of 513 cases. Am J Surg Pathol 30:11559, 2006. 
  6. Griepp RB, Ergin MA, Lansman SL, et al. The natural history of thoracic aortic aneurysms. Semin Thorac Cardiovasc Surg 1991; 3:258.
  7. Connolly ES Jr, Rabinstein AA, Carhuapoma JR, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association. Stroke 2012; 43:1711.
  8. Shreibati JB, Baker LC, Hlatky MA, Mell MW. Impact of the Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act on abdominal ultrasonography use among Medicare beneficiaries. Arch Intern Med 2012; 172:1456. 
  9. Gadowski GR, Pilcher DB, Ricci MA. Abdominal aortic aneurysm expansion rate: effect of size and beta-adrenergic blockade. J Vasc Surg 1994; 19:727. 
  10. Johnston KW, Rutherford RB, Tilson MD, et al. Suggested standards for reporting on arterial aneurysms. Subcommittee on Reporting Standards for Arterial Aneurysms, Ad Hoc Committee on Reporting Standards, Society for Vascular Surgery and North American Chapter, International Society for Cardiovascular Surgery. J Vasc Surg 1991; 13:452. 



Media References

  1. Aneurysem, CC BY-SA 3.0

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