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Neuroradiology

Mycotic aneurysm, in bacterial endocarditis

a focal dilatation of an artery subsequent to infection of its wall, necrosis and weakening. As it is usually associated with bacterial endocarditis the term is inappropriate since the pathogenetic agents are usually bacteria and not a fungus. In this case it should then be called bacterial and not mycotic.

Endocarditis is a bacterial infection of the heart valves or of the endocardium. It may be acute or subacute depending on the pathogenicity of the microorganism involved.

It occurs most frequently in people with pre-existing heart disease. The bacteria most commonly involved are Staphylococcus aureus, pneumococcus, group A streptococcus.

The pathogenesis of bacterial aneurysms is believed to start when an infected embolus lodges at some point in the vessel wall; infection, inflammation and necrosis leads to weakening of the wall and focal aneurysmal dilatation following pulsations. These are in fact pseudoaneurysms and should not be called mycotic, but more properly bacterial, since the pathogenetic agent is usually not a fungus.

They occur most frequently on the middle cerebral artery or its distal branches, less commonly on the posterior and anterior cerebral arteries. They appear in about 2% of cases of bacterial endocarditis. They have a very high tendency to rupture and bleed intraparenchymally, producing cerebral haematomas.

Such aneurysms frequently rupture and bleed. Emergency CT (Fig.1) usually shows an intracerebral haematoma, and angiography demonstrates the presence of the pseudoaneurysm usually along the course of a distal branch of the middle cerebral artery or less frequently along the anterior and posterior cerebral arteries.

Their treatment is either surgical, in which case the parent vessel must be sacrificed, or endovascular with emergency glue injection and sacrifice of the parent artery if distal. They tend to recur in different locations.

GS

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Fig.1

a. Axial CT without contrast. Left temporoparietal haematoma with intraventricular haemorrhage, in a young patient that presented with headache, aphasia and progressive impairment of consciousness. b. Left internal carotic angiogram. An aneurysm is seen along the course of a parietal branch of the middle cerebral artery. c. Following emergency endovascular embolization with glue, the aneurysm is occluded together with part of the distal parietal branch.
Mycotic aneurysm, in bacterial endocarditis, Fig.1 (a)
Mycotic aneurysm, in bacterial endocarditis, Fig.1 (b)
Mycotic aneurysm, in bacterial endocarditis, Fig.1 (c)