Cerebral abscess (summary)

• this

  This is a basic article for medical students and non-radiologists

Cerebral abscesses are foci of infection in the brain parenchyma. They typically have enhancing walls but can mimic a number of other significant pathologies.

Epidemiology

All age groups are susceptible to development of cerebral abscesses, however some areCerebral abscess may occur at highany age, although risk, including increases in certain groups including those with systemic infection or remote abscesses and IVDAs, remote abscess and in those who use intra-venous drugs ¹.

Clinical presentation

Neurological symptoms are more common than overt infective signssigns of infection. Signs of raised intracranial pressure, focal neurological changesneurology or seizures are signs to lead toshould prompt imaging and investigation.

Pathology

Abscesses develop following spread of bacteria to brain tissues. Initially there will be inflammation and irritation of parenchyma before a typical walled "abscess" forms.

Haematogenous spread is the commonest route for bacteria to enter the brain ¹. Lesions can make their way to the peripheries (where vessels get smaller and bacteria get lodged). Direct spread from upper respiratory or scalp infections contribute to some cases but fewer than historically.

Microbiology

There can be mixed bacteriology, with common pathogens in the Streptococcal groups ¹. Sterile cultures can be found in 25-34% of cases ^1,2. Gram negative bacteria are commoner in paediatric cases and immunocompromised patients are at risk to other opportunistic pathogens.

Radiological features

MRI is the best method of investigating cerebral abscesses ³ but there are some signs on CT which is usually more readily available.

CT

Post-contrast views are usually required to be of use in abscess diagnosis. Better in advanced cases, where the wall of the abscess ("ring enhancing lesion") can be visualised with central and surrounding hypodensities (consisting of pus and oedema, respectively).

MRI

There are a number of features that MRI shows in abscess formation. These are described in the main article which again illustrate the enhancing rim, fluid/pus filled cavity (with restricted diffusion) and surrounding oedema.

MRI can be used to guide drainage and monitor response to treatment in follow-up imaging.

Treatment and prognosis

These deep-seated infections usually require neurosurgical involvement for drainage or craniotomy as well as intensive intravenous broad spectrum antibiotics ¹.

Differential diagnosis

A number of conditions can mimic the appearance of cerebral abscesses. This is the reason why expert care and treatment is required.

Differentials include:

• tumours
  • primary CNS tumour
  • metastasis
• demyelination
• infarction or haemorrhage
• post-treatment changes e.g. radiation necrosis

More information

• brain abscess