Septic-embolic encephalitis

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

Terminology

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

Epidemiology

In most series CNS involvement, CNS involvement during the course of infective endocarditis occurs occurs in ~30% (range 20-40%) of cases². 

Clinical presentation

Ischaemic stroke is the most common mode of presentation of patients with SEE¹. Symptoms can vary from headache to unconsciousness 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 mechanismmechanisms of brain damage ⁴:

• occlusion of cerebral arteries by septic and thrombotic emboli (e.g. arising from heart valve vegetations): it can can result in focal ischaemia, cerebral haemorrhage, or both
• meninges, brain parenchyma 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-mediated injury

Aetiology 

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

Radiographic features

In almost 90% of cases SEE, SEE findings occursoccur in the distribution of middle cerebral 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 along with hyperdense haemorrhagic areas may be spotted in the anterior circulation territories. Contrast-enhanced images 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 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