Cerebral abscess
A cerebral abscess is a focal collection of pus within the brain parenchyma (a big pus tumour). Abscesses may occur in single or multiple sites, and the site of collection correlates with the sourc eof infection. Initial infection leads to suppuration and loculation of pus, followed by gliosis and formation of a fibrous capsule. Cerebral abscess presents with focal neurological deficits and signs of raised intracranial pressure. Empiric therapy should not be delayed, however, getting a sample for culture and sensitivity to know the bacteria present is appropriate.
Organisms are commonly introduced via a contiguous spread. Streptococcus and staphylococcus species are the most common bacteria responsible though most infections are polymicrobial.
Site of abscess, source of infection, and likely organism
| Site | Source of infection | Likely organism |
|---|---|---|
| Frontal lobe | Sinusitis, dental infection, bacteremia, emolism from infective endocarditis | Streptococcus pneumoniae, Anaerobes |
| Temporal lobe and cerebellum | Otitis media, mastoiditis, bacteremia, embolism from infective endocarditis | Streptococcsu pneumoniae, Gram negative bacilli, Bacteroides and anaerobes |
| Parietal lobe | Bacteremia, embolism from infective endocarditis | Streptococcsu pneumoniae, Gram negative bacilli, Bacteroides and anaerobes |
| Any site | Trauma | Staphylococcus aureus |
Causative organisms
| Organism | Population |
|---|---|
| Streptococcus and staphylococcus | Most common cause |
| Klebsiella | Diabetes |
| Staphylococcus epidermidis | Iatrogenic |
| Candida | Immunocompromised |
| Tuberculosis | Rare but important in Sub-saharan Africa |
- Risk factors in adults
- Lung infection
- Dental abscess
- Sinusitis
- Otitis
- Mastoiditis
- Endocarditis
- Risk factors in children
- Cyanotic heart disease
- Pulmonary arteriovenous malformation
- Predisposing factors
- Diabetes
- Chronic steroid use
- Sarcoidosis
- HIV
- Immunosuppression
- Organ transplant
- Recent cranial or dental procedure
- Signs and symptoms
- Investigations
- Head CT: The best first diagnostic step to locate the abscess. Will clearly show the abscess
- Single ring-enhancing lesion typically at the grey-white matter junction and watershed areas
- Multiple foci of abscesses in case of toxoplasmosis
- MRI:
- Ring enhancement
- Hyperintense on T2
- Aspiration biopsy: Most accurate test; will show us what causative organism
- Labs: CBC, ESR, CRP
- Lumbar puncture: delayed when there are signs of raised ICP. May show features of bacterial meningitis.
- Head CT: The best first diagnostic step to locate the abscess. Will clearly show the abscess
- Differentials for a solitary ring-enhancing lesion (MAGICAL DR)
- Metastasis
- Abscess
- Glioblastoma
- Infarct
- Contusion
- Aneurysm
- Lymphoma
- Demyelinating disease
- Radiation necrosis
- Treatment
- Empiric IV antibiotics while preparing for surgery or until lesions decrease to < 1cm on MRI. A minimum of 6 – 8 weeks antibiotics is given. Antibiotics have to penetrate the blood brain barrier and capsule. Commonly metronidazole + ceftriaxone + vancomycin
- IV oxacillin OR nafcillin OR vancomycin OR linezolid – cover staphylococcus
- IV penicilln G: cover streptococcis
- IV clindamycin OR metronidazole – cover anaerobes. Clindamycin has poor CNS penetration compared to metronidazole
- IV 3rd gen cephalosporin (Ceftriaxone, Cefotaxime) – cover gram negatives and Streptococcus
- IV ceftazidime OR cefepime OR carbapenems – for nosocomial infection or neurosurgery to cover drug resistant gram negative
- If the patient has AIDS (presumed toxoplasmosis)
- Pyrimethamine AND Sulfadiazine (Surgery not necessary, will respond in 10-14 days)
- If they do not respond, exclude abscess and consider a CNS lymphoma
- Surgical drainage if the abscess if > 2.5 cm, mass effect, signs of raised ICP or clinical deterioration
- Antiepileptic agents in the acute and peri-operative period (abscesses commonly cause seizures, especially those in the frontal and temporal lobe)
- Short courseo of glucocorticoids if there is significant mass effect
- Empiric IV antibiotics while preparing for surgery or until lesions decrease to < 1cm on MRI. A minimum of 6 – 8 weeks antibiotics is given. Antibiotics have to penetrate the blood brain barrier and capsule. Commonly metronidazole + ceftriaxone + vancomycin
- Indications for surgery for brain abscess
- Abscess > 2.5 cm
- Mass effect
- Signs of raised ICP
- Clinical deterioration
Empyema
An empyema is a collection of purulent material, commonly in the subdural space. It can also occur in the epidural space. They were historically referred to as abscesses, but the term empyema is preferred now. The clinical presentation is similar to meningitis. A subdural empyema is a surgical emergency. Antibiotics alone won’t control infection.
- Risk factors
- ENT infection (sinusitis, otitis, mastoiditis)
- Skull trauma
- Neurosurgical procedure
- Meningitis
- Signs and symptoms
- Fever
- Headache
- Vomiting
- Altered mental status
- Seizure
- Investigations
- CT or MRI: diagnostic method of choice. It may be difficult to locate a collection in the posterior fossa on CT.
- Crescent or elliptical collection of hypo intensity on T1 MRI
- Mass effect or midline shift may be present
- Aspirate for culture and sensitivity
- CT or MRI: diagnostic method of choice. It may be difficult to locate a collection in the posterior fossa on CT.
- Treatment
- IV broad spectrum antibiotics for at least 6-8 weeks
- Surgical drainage
- Anti-epileptic medication for seizure prophylaxis
- Craniectomy and extension of duration of antibiotics if there is adjacent osteomyelitis