Septic-embolic encephalitis

Septic-embolic encephalitis (SEE), also referred as septic-embolic brain abscess, corresponds to a focal or diffuse brain infection, ischaemic and haemorrhagic damages following an infective thromboembolism from any part of the body ¹. It is usually caused by bacterial infections from endocarditis. 

Terminology

Septic-embolic encephalitismust be differentiated from sepsis-associated encephalopathy, which is a clinical syndrome related to a diffuse brain dysfunction in the context of sepsis and without overt central nervous system (CNS) infection ⁵.

Epidemiology

In most series CNS involvement during the course of infective endocarditis occurs in 20% to 40% of cases ². 

Clinical presentation

Symptoms can vary from headache to unconsciousness, the most common are ^1,3: fever, toxic encephalopathy (characterised by mental status changes and psychosis), meningism signs, headache and seizures. 

Ischaemic stroke is the most common mode of presentation of patients with SEE ¹. 

Risk factors:

• cardiac disease:
  • rheumatic cardiovascular disease
  • mitral valve prolapse
  • prosthetic cardiac valves
  • congenital heart disease 
• drug addiction (intravenous drugs)
• immunocompromised patients 
• central venous catheter 
• arteriovenous shunts  

Pathology 

In a context of an infectious site in the body, some aetiological agents can get in the CNS carried by arterial blood. The most common explanations for this are ^1-4: 

• infections on heart left chambers (aortic and mitral valve endocarditis)
• pulmonary infectious 
• infections in other body sites that can get the arterial circulation by an arteriovenous shunt

There are three main pathogenic mechanism of brain damage ⁴:

• occlusion of cerebral arteries by septic and thrombotic emboli (e.g. arising from heart valve vegetations): it can result in focal ischaemia, cerebral haemorrhage, or both
• meninges, brain, parenchyma, or vascular walls infection by septic emboli or bacteremia. Numerous microabscesses can be seen and occasionally they coalesce to form space-occupying macroabscesses.
• toxic and immune mediated injury

Aetiology 

• Staphylococcus aureus (most common)
• Streptococcus viridans
• fungal infections infection

Radiographic features

In almost 90% of cases SEE findings occurs in the distribution of middle cerebral artery (MCA) due the anatomical circulation features that favoured it, and rarely in the posterior circulation ¹. 

CT/MRI 

MRI is superior to CT in depicting the different stages of SEE evolution.

Hypodense areas of ischaemic infarction along with hyperdense haemorrhagic areas may be spotted in the anterior circulation territories. Contrasted images are essential to evaluate abscess formation. 

Local arteritis can promote mycotic aneurysm and vascular ruptures.

Treatment and prognosis

Prompt institution of empiric antimicrobial treatment must be done until the results of culture are available. In cases that emboli continue to form despite antimicrobial treatment, surgical heart valve replacement may be necessary. Mycotic aneurysm: many regress spontaneously under clinical treatment, however persistent ones may need surgical or endovascular treatment ⁴.

See also

• CNS infectious diseases

• septic pulmonary emboli