Septic-embolic encephalitis

Septic-embolic encephalitis (SEE), also known as septic-embolic brain abscess, refers to a focal or diffuse brain infection, ischaemic and haemorrhagic damages following an infective thromboembolism from any part of the body. 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 without overt central nervous system (CNS) infection ⁵.

Epidemiology

In most series, CNS involvement during the course of infective endocarditis occurs in ~30% (range 20-40%) of cases ². 

Clinical presentation

Ischaemic stroke is the most common mode of presentation of patients with SEE ¹. Symptoms can vary from headache to unconsciousness, the most common are ^1,3: 

• fever
• toxic encephalopathy: characterised by mental status changes and psychosis
• meningism
• headache
• seizures

Risk factors

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

Pathology 

Some aetiological agents can get in the CNS carried by arterial blood from multiple systemic infectious foci ^1-4: 

• left-sided cardiac infections (i.e. aortic and mitral valve endocarditis)
• pulmonary infections
• infections in other body sites that can get the arterial circulation by an arteriovenous shunt

There are three main pathogenic mechanisms 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 infection

Radiographic features

In almost 90% of cases, SEE findings occur in the distribution of middle cerebral artery (MCA) (due to favoured anatomy), 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. Contrast-enhanced images are essential to evaluate abscess formation. 

Local arteritis can promote mycotic aneurysm formation and vascular rupture.

Treatment and prognosis

Prompt administration of empiric antibiotics until the results of culture are available is vital. 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 aneurysms may need surgical or endovascular treatment ⁴.

See also

• CNS infectious diseases
• septic pulmonary emboli