However, in the case of mycotic aneurysm the microorganism associated with the aneurysm is bacterial in nature. They are often multiple and may involve any vessel. Aneurysms may develop despite appropriate antibiotic therapy, although resolution of small lesions during medical therapy has been demonstrated. Pathogenesis Mycotic aneurysms develop more often in patients with subacute infective endocarditis. These aneurysms develop secondary to the implantation of circulating bacteria in a diseased atherosclerotic or traumatized intima, with wall separation and aneurysm formation.
Atherosclerotic lesions are perhaps a prerequisite for the development of such aneurysm.
The implantation of bacteria upon ulcerated atheromatous plaques leads to inflammation with thinning of arterial walls, necrosis, and possible hemorrhage. Another mechanism of infection is from direct extension or through lymphatic vessels from an adjacent infectious lesion. Mycotic aneurysm occurs less frequently in patients with acute infective endocarditis and is more likely to be a result of septic microemboli entering the vaso vasorum causing focal necrosis of the vessel wall. These lesions tend to rupture earlier and more frequently than in subacute disease. When mycotic aneurysms are discovered in a patient with acute infective endocarditis, surgical resection should be undertaken promptly to avert the risk of rupture and serious morbidity or death.