Diagnosis

Brain abscess

Etiology

Cause - The 3 mechanisms of entry into the brain [ukh]

1. Direct extension: Infections stemming from the sinuses, teeth, middle ear, or mastoid may gain access to the venous drainage of the brain. Due to improved antibiotic therapy for ear infections, this mechanism is decreasing in incidence, accounting for only approximately 12-25% of cases. However, in developing countries, this is still a significant source accounting for at least 50% of cases.

   • Microbe: Streptococcus, Bacteroides, Enterobacteriaceae, Pseudomonas, Fusobacterium, Prevotella, Peptococcus, Propionibacterium.

2. Hematogenous: Seeding of the brain occurs from distant infection sites and often results in multiple brain abscesses.

   • Microbe: Streptococcus viridans, Staphylococcus aureus, Fusobacterium, Corynebacterium, Peptococcus species, Klebsiella species, E coli + other Enterobacteriaceae, Streptococcus species, anaerobes and Pseudomonas.

3. Penetrating head injury or neurosurgery: A case series found that 37% of brain abscesses were associated with head penetration.

   • Microbe: Penetrating head injury or neurosurgery: Staphylococcus aureus, gram-negative bacilli, Staphylococcus epidermidis, Clostridium species, anaerobes, Pseudomonas and Propionibacterium acnes.

Opportunistic infection in immunecompromised state: Toxoplasma gondii, Nocardia, Aspergillus, and Candida species.

Pathophysiology

1. Entry to the brain parenchyma

2. Inflammation during the early cerebritis stage

3. Evolves into a necrotic collection of pus

4. Eventually surrounded by a well-vascularized capsule after 2 weeks --> abscess

Risk factors [sri]

• Penetrating head trauma / neurosurgery

• Infections: dental infection, ear, sinusitis, endocarditis, pneumonia

• Intravenous drug use

• Cardiac abnormalities

• Congenital heart disease

• Diabetes

• Immunocomprimised: steroid use, HIV, immunosuppression

• Alcoholism

• Neoplasm

Epidemiology

Incidence per 100.000 [sqw][npd][crc][asn][sri]

Approach

• Blood test: complete blood count, platelet count, ESR, CRP, serological testing [ukh]

• Blood culture

• Lumbar puncture

• CT caput

• MR caput

• MR Spectroscopy

• Brain biopsy / culture

Treatment

1. Antibiotic treatment (i.v.) for 6–8 weeks [sri][ukh]

2. Neurosurgical aspiration: depends on the location, size (>2.5cm), and the clinical condition [sri]

3. Corticosteroids: Controversial due to its immunosuppressive effect. Consider if profound edema with brain shift and risk of cerebral herniation [sri]

Differential diagnoses

Brain tumor, Candidiasis, Cat scratch disease, Cerebral venous sinus thrombosis, Cluster headache, Cryptococcosis, Encephalitis, Epidural hematoma, Febrile seizure, Intracerebral hemorrhage, Malignant hypertension, Meningitis, Migraine, Multiple sclerosis, Mycotic cerebral aneurysm, Neurocysticercosis, Parasitic infestations, Retinal artery occlusion, Spinal cord infection, Stroke, Subarachnoid hemorrhage, Subdural empyema, Tension headache, Tuberculosis