Overview
Brain abscesses are serious and potentially life-threatening collections of pus usually secondary to bacterial infection and trauma. They often present with features similar to causes of raised intracranial pressures, such as tumours.
The organism may enter the brain through direct extension or haematogenous spread, such as in infective endocarditis.
Epidemiology
- Rare in developed countries and more prevalent in the developing world
- More common in children with cyanotic congenital heart disease
- Prevalence is higher in people with HIV and organisms are usually opportunistic fungi/protozoa
Causes
Bacterial causes
- Streptococcus pyogenes
- Staphylococcus aureus
- Neisseria meningitidis
Fungal causes
- Aspergillus species
- Candida species
Parasitic causes
- Toxoplasma gondii
- Entamoeba histolytica
Other causes
- Spread from other infections e.g. upper respiratory tract infection
- Haematogenous spread e.g. infective endocarditis
Risk Factors
- Meningitis
- Upper respiratory tract infection, particularly sinusitis
- Otitis media
- Congenital heart disease
- Endocarditis
- Diabetes mellitus
- Any cause of immunodeficiency e.g. HIV
- Haemodialysis
- Recent brain trauma/surgery
Presentation
Patients commonly present with fever and signs of raised intracranial pressure. They may have a history of prior infection. Some features may be:
- Headaches – often dull and persistent and can worsen with changes in posture
- Fever – may not be swinging, unlike abscesses at other sites in the body
- Features of raised intracranial pressure:
- Nausea/vomiting
- Papilloedema
- Seizures
- Focal neurological deficits
- CN III palsy: ptosis, dilated and fixed pupil, eye is ‘down and out’
- CN VI palsy: impaired eye abduction, horizontal diplopia
- Meningism:
- Neck stiffness
- Photophobia
Differential Diagnoses
Brain tumours
- They may present similarly but fevers and meningism are less likely
- Symptoms usually last longer over several weeks to months
Investigations
- Full blood count (FBC):
- May show leukocytosis
- C-reactive protein (CRP)/erythrocyte sedimentation rate (ESR):
- Non-specific markers of inflammation
- May be elevated
- Blood cultures:
- May be positive
- Serum toxoplasma titres:
- If HIV/immunodeficiency suspected
- CT head with and without contrast:
- May show ring-enhancing lesions
- MRI with contrast – ideal but more time–consuming and expensive
- May show ring-enhancing lesions
Management
- 1st-line: IV ceftriaxone + metronidazole antibiotics
- If toxoplasmosis: amphotericin/fluconazole/voriconazole
- If fungal cause: pyrimethamine + sulfadiazine
- Definitive management: craniotomy and surgical evacuation
- Consider IV dexamethasone if CT scanning shows massive cerebral oedema
Complications
- Seizures
- Ventriculitis – due to rupture of abscess in the ventricular system, can lead to hydrocephalus
- Syndrome of inappropriate ADH secretion (SIADH) – leads to hyponatraemia
- Permanent neurological deficits
Prognosis
- The prognosis is poorer in people who are immunodeficient, have diabetes mellitus or have a low Glasgow Coma Score
- Ventricular rupture is associated with a high mortality
