Mycotic aneurysm

Dr Donna D'Souza et al.

Mycotic aneurysms are aneurysms arising from infection of the arterial wall, usually bacterial. It is a complication of the haematogenous spread of bacterial infection, classically from the heart. 

The epidemiology of mycotic aneurysms mirrors that of identifiable risk factors: 

  • infective endocarditis (common)
  • intravenous drug use
  • immunosuppression
  • iatrogenic arterial trauma
  • pre-existing atherosclerotic plaque or a native aneurysm
  • prosthetic arterial devices (e.g. stents and grafts)
  • direct arterial involvement from adjacent infection

The vessel wall becomes infected with bacteria, is digested and a false aneurysm forms, which is unstable and highly prone to rupture. The most common organisms are Staphylococcus aureus and Salmonella species. Mechanisms of infections include:

  • septicaemia
  • septic emboli
  • contiguous spread from adjacent infection
Location

Frequently found in atypical locations. The most common sites are:

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

Described features include the following (some are however nonspecific):

  • saccular
  • centric aneurysmal sac in an odd location for atheromatous disease
  • 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

Mycotic aneurysms carry a very high mortality.

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

The term "mycotic" (meaning fungus) was coined in 1885 by Canadian physician Sir William Osler (1849-1919) on describing the gross pathological appearance of two small saccular aortic aneurysms, not the underlying pathological organism 9

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Article information

rID: 1706
System: Vascular
Section: Pathology
Synonyms or Alternate Spellings:
  • Mycotic aneurysms

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