Aneurysm (Definition & Types of aneursym)

Aneurysms An aneurysm is a localized abnormal dilation of a vessel due to weakening of the vessel wall. Aneurysms are classified by shape and size and can thus be considered saccular or fusiform aneurysms. A saccular aneurysm is a spherical out-pouching that involves only a portion of the blood vessel. This type of aneurysm measures 5 to 20 cm in diameter. A fusiform aneurysm involves diffuse and circumferential dilation of a long segment of a vessel and can range in size, but can reach 20 cm in diameter. Thoracic aortic aneurysm is a balloon-like dilation of the aorta that occurs due to weakness of the aortic wall and is often a complication of a tertiary syphilis infection. Tertiary syphilis causes endarteritis of the vasa vasorum of the ascending and transverse portions of the aortic arch, which generates luminal narrowing, decreased flow, and atrophy of the vessel wall. On gross examination the aorta has a “tree bark” appearance. Thoracic aortic aneurysms can lead to dilation of the aortic valve root resulting in aortic valve insufficiency/regurgitation. Complications of a thoracic aortic aneurysm include the compression of mediastinal structures (i.e. airway, esophagus), thrombosis and embolism. The left recurrent laryngeal nerve can be stretched causing a brassy cough and voice hoarseness. Treatment should include antibiotics for tertiary syphilis. Abdominal aortic aneurysm is a balloon-like dilation of the abdominal aorta present below the renal arteries but above the aortic bifurcation. Abdominal aortic aneurysms are most commonly caused by atherosclerosis and are usually seen in hypertensive male smokers older than 60 years of age. Atherosclerosis increases the diffusion barrier to the media creating atrophy and weakness in the vessel wall. Below the renal arteries there are no vasa vasorum; therefore, the aorta must rely on diffusion for getting oxygen and nutrients. Normally presents as a pulsatile abdominal mass that grows with time. The major complication of an abdominal aortic aneurysm is rupture, which presents with a triad of hypotension, pulsatile abdominal mass, and flank pain, usually localized to the left side. The risk is increased when the diameter of the aneurysm in greater than 5 cm. Additional complications associated with abdominal aortic aneurysms include the compression of local structures such as the ureters and thrombosis and embolism. Treatment of thoracic and abdominal aneurysms often involves surgical intervention or in some cases watchful waiting in combination with control of blood pressure. Berry aneurysm: small saccular lesions in the circle of Willis that develop at sites of congenital medial weakness, rupture causes subarachnoid hemorrhage, and is unrelated to atherosclerosis Defect at the junction of communicating branches with main cerebral vessels because these areas lack internal elastic lamina and smooth muscle (tunica media) layers. Associations: autosomal dominant polycystic kidney disease, Ehlers Danlos syndrome, Marfan’s syndrome, and coarctation of the aorta Mycotic aneurysm: misnomer because vessel wall weakening can be due to a bacterial or fungal agent that usually arise at the lodging sites of emboli Fungal vessel invaders: Aspergillus, Candida, Mucor Bacterial vessel invaders: Bacteroides fragilis, Pseudomonas aeruginosa, Salmonella.