Brain Abscess

Content of This Page

 1- Introduction

2- Causes

3- Symptoms

4- Causative Agents

5- Investigations & Lab Results

6- Complications

7- Treatment

Introduction

A brain abscess is a localized collection of pus within the brain tissue, typically caused by a bacterial or fungal infection. It results from inflammation and infection, often secondary to infections elsewhere in the body, such as sinusitis, otitis media, dental infections, or hematogenous spread from distant sites (e.g., lungs or heart). The abscess forms when the immune system attempts to contain the infection, leading to a capsule surrounded by inflamed brain tissue.

 
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Causes

1. Direct Extension from Nearby Infections

  • Otitis media or mastoiditis → temporal lobe or cerebellar abscess

  • Sinusitis (especially frontal or ethmoid sinuses) → frontal lobe abscess

  • Dental infections → frontal lobe abscess

2. Hematogenous Spread (from distant infections via bloodstream)

  • Lung infections (e.g., lung abscess, bronchiectasis, empyema)

  • Congenital heart disease with right-to-left shunts (e.g., Tetralogy of Fallot)

  • Skin or abdominal infections in immunocompromised patients

3. Post-traumatic or Post-surgical

  • Penetrating head trauma

  • Neurosurgical procedures

4. Immunocompromised States

  • HIV/AIDS

  • Immunosuppressive therapy (e.g., transplant patients)

  • Malignancy

-Common Organisms

  • Aerobic and anaerobic streptococci

  • Staphylococcus aureus

  • Gram-negative bacilli

  • Fungal and parasitic agents (e.g., Toxoplasma in immunocompromised patients)

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Symptoms

-General Symptoms

  • Headache (most common and often localized)

  • Fever (may be absent in immunocompromised individuals)

  • Nausea and vomiting

  • Altered mental status (confusion, drowsiness, or coma)

-Focal Neurological Deficits

  • Weakness or numbness on one side of the body (hemiparesis)

  • Speech disturbances (if dominant hemisphere is involved)

  • Visual disturbances (e.g., visual field defects)

  • Seizures (especially in cortical involvement)

-Signs of Increased Intracranial Pressure (ICP)

  • Papilledema (on fundoscopic exam)

  • Drowsiness or coma in severe cases

  • Cranial nerve palsies (due to pressure or location of abscess)

Causative Agents

1. Bacteria

  • Aerobic bacteria:

    • Staphylococcus aureus (most common, especially in post-traumatic or post-surgical abscesses)

    • Streptococcus species (especially viridans group streptococci)

    • Enterobacteriaceae (e.g., E. coli, Klebsiella)

  • Anaerobic bacteria:

    • Bacteroides species

    • Fusobacterium species

    • Peptostreptococcus species

These anaerobic and aerobic bacteria often cause brain abscesses secondary to infections like sinusitis, otitis media, dental infections, or from contiguous spread.

2. Fungi

  • Candida species (in immunocompromised patients)

  • Aspergillus species

  • Cryptococcus neoformans

  • Other molds or yeasts (usually in immunocompromised patients)

3. Parasites

  • Toxoplasma gondii (especially in immunocompromised patients like those with HIV/AIDS)

  • Echinococcus (causing hydatid cysts that can mimic abscesses)

Investigations & Lab Results

1. Imaging Studies

-CT Scan with Contrast (Preferred Initial Test)

  • Shows a ring-enhancing lesion with surrounding edema.

  • Helps determine size, number, and location of abscesses.

  • May show mass effect or midline shift.

-MRI with Contrast

  • More sensitive than CT, especially in early stages.

  • Differentiates abscess from tumors or infarcts.

2. Neuroimaging-Guided Aspiration

  • Stereotactic aspiration or surgical drainage allows:

    • Confirmation of diagnosis

    • Microbiological identification of causative organisms

3. Laboratory Tests

Blood Tests

  • Complete Blood Count (CBC):

    • Elevated WBC count (leukocytosis)

  • Erythrocyte Sedimentation Rate (ESR) / C-Reactive Protein (CRP):

    • Typically elevated, indicating inflammation

  • Blood cultures:

    • May detect causative organism, especially in hematogenous spread

CSF Analysis (Lumbar Puncture)

  • Usually contraindicated if there is raised intracranial pressure (risk of herniation).

  • Done only if imaging excludes mass effect.

Complications

1. Increased Intracranial Pressure (ICP)

  • Due to mass effect from the abscess and surrounding edema

  • Can lead to brain herniation, which is life-threatening

2. Brain Herniation

  • Compression and displacement of brain structures

  • Can result in coma or death

3. Seizures

  • Common both during and after infection

  • May become chronic (epilepsy), especially with cortical involvement

4. Neurological Deficits

  • Depending on location, may include:

    • Hemiparesis

    • Speech disturbances

    • Visual deficits

    • Cognitive impairment

5. Abscess Rupture into Ventricles

  • Causes ventriculitis or meningitis

  • Associated with a very poor prognosis

6. Recurrence or Residual Abscess

  • If not fully treated or drained

  • May require repeated surgical intervention

7. Hydrocephalus

  • Due to obstruction of CSF pathways from inflammation or abscess pressure

Treatment

1. Medical Management

Empiric Antibiotic Therapy (IV)

  • Started immediately after diagnosis, and adjusted once cultures are available.

  • Typical empiric regimen:

    • Ceftriaxone or cefotaxime (broad-spectrum coverage)

    • Metronidazole (for anaerobic organisms)

    • Vancomycin (if Staphylococcus aureus or MRSA is suspected)

2. Surgical Management

Indications:

  • Abscess > 2.5 cm in diameter

  • Significant mass effect or midline shift

  • Failure to improve with antibiotics alone

  • Uncertain diagnosis requiring tissue sample

Procedures:

  • Aspiration (stereotactic or open): Removes pus and provides material for culture

  • Surgical excision: For multiloculated, recurrent, or inaccessible abscesses

3. Management of Complications

  • Anticonvulsants to prevent or treat seizures

  • Mannitol or corticosteroids to reduce cerebral edema (used cautiously)

  • Treatment of increased ICP or hydrocephalus (e.g., ventricular drainage)

4. Supportive Care

  • Close neurological monitoring

  • Management of underlying source (e.g., ear, sinus, dental infections)

  • Rehabilitation for any neurological deficits

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