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Mycotic aneurysm

Dr Yuranga Weerakkody and Dr Donna D'Souza et al.

A mycotic aneurysm is an aneurysm arising from bacterial infection of the arterial wall. It can be a common complication of the haematogenous spread of bacterial infection ⁴.

Pathogenesis

The vessel wall is digested and a false aneurysm forms which is unstable and highly prone to rupture.

Mechanisms of infection

septicaemia
septic emboli
contiguous spread from adjacent infection

Risk factors

bacteraemia
infective endocarditis
intravenous drug use
immunosuppression
iatrogenic aortic trauma
pre existing atherosclerotic plaque or native aneurysm
prosthetic arterial devices (stents, grafts)

The commonest organisms are Staphylococcus and Salmonella.

Location

Frequently found in atypical locations. The commonest sites are

thoracic and abdominal aorta
abdominal visceral arteries
lower extremity arteries
intracranial arteries : typically more peripheral than berry aneurysms

Radiographic features

CT - CT angiography

Described features include the following (some are however non specific)

saccular
ccentric aneurysmal sac in an atypical location for atheromatous diseas
often wild, multilobulated appearance
interruption of arterial wall calcification
adjacent soft tissue stranding
adjacent collection + / - gas
adjacent reactive lymphadenopathy
hazy aortic wall with rupture ⁴
retroperitoneal para-aortic fluid collection and vertebral erosion
thrombus formation within a false lumen after aneurysmal rupture

Complications

aneurysmal rupture (high risk) with haemorrhage
ongoing source of sepsis
embolic infarction

Prognosis

Carries a very high mortality

Differential diagnosis

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