Brain Abscess

Erica Hardy, M.D., M.M.S.

Basic Information

Definition

A brain abscess is a focal intracerebral infection that can arise as a complication of a bacterial, mycobacterial, fungal, or parasitic infection, surgery, or trauma.

ICD-10CM CODES
G06.0	Intracranial abscess and granuloma

Epidemiology & Demographics

Incidence

•

Uncommon (reported incidence 0.4 to 0.9 cases per 100,000 population; occurs about 2% as commonly as brain tumors)

Peak Incidence

•

Preadolescence and middle age (and depends on predisposing condition); increased rates in the immunocompromised host

Predominant Age

•

Occurs at any age

Predominant Sex

•

Men affected more than women (ratio 2:1 to 3:1)

Physical Findings & Clinical Presentation

•

Classic triad: fever, headache, and focal neurologic deficit (present in approximately 20% of cases).
•

Clinical presentation is often due to the manifestations of the space-occupying lesion rather than to signs of systemic infection.
•

Fever is present in only 32% to 79% of patients.
•

Headache is usually localized to the side of the abscess; onset can be gradual or severe; present in an average of 70% to 75% of cases.
•

Focal neurologic findings (e.g., seizures, hemiparesis, aphasia, ataxia) depend on the location of the abscess and are seen in 23% to 66% of cases.
•

Papilledema is present in 9% to 51% of cases.
•

Presence of adjacent infections (dental abscess, otitis media, sinusitis, or postneurosurgical infection) may be a clue to the underlying diagnosis and should be sought in any suspected case.
•

Time course from symptom onset to presentation ranges from hours in fulminant cases to more than 1 month; 75% present in the first 2 weeks.
•

The nonspecific presentation of a brain abscess warrants that clinicians maintain a high index of suspicion. Table 1 describes common initial features of brain abscess.

TABLE1 Brain Abscess: Initial Features in 123 CasesFrom Goldman L, Schafer AI: Goldman’s Cecil medicine, ed 24, Philadelphia, 2012, Saunders.

Headache 55%

Disturbed consciousness 48%

Fever 58%

Nuchal rigidity 29%

Nausea, vomiting 32%

Seizures 19%

Visual disturbance 15%

Dysarthria 20%

Hemiparesis 48%

Sepsis 17%

Etiology

•
Brain abscesses are classified based on the likely portal of entry and can arise from:
1. Contiguous infection (e.g., dental abscess, otitis media, sinusitis, or post neurosurgical infection)
2. Hematogenous spread from a remote site (e.g., endocarditis, bacteremia)
•
Likely source of abscess and common organisms involved:
1. A.
  Contiguous focus or primary infection (55% of all brain abscesses):
  1. 1.
    
    Paranasal sinus: occur in frontal lobe; streptococci (especially microaerophilic and anaerobic streptococci), Bacteroides, Haemophilus, and Fusobacterium spp.
  2. 2.
    
    Otitis media/mastoiditis: occur in temporal lobe and cerebellum; aerobic and anaerobic streptococci, Enterobacteriaceae, Bacteroides, and Pseudomonas spp.
  3. 3.
    
    Dental infection: occur in frontal lobe; mixed Fusobacterium, Bacteroides, and Streptococcus spp. (especially S. viridans and anaerobic streptococci)
  4. 4.
    
    Penetrating head injury: site of abscess depends on site of wound; Staphylococcus aureus, aerobic streptococci, Clostridium spp., Enterobacteriaceae
  5. 5.
    
    Postoperative: Staphylococcus epidermidis and S. aureus, Enterobacteriaceae, and Pseudomonas aeruginosa
2. B.
  Hematogenous spread from a distant site of infection (25% of all brain abscesses): abscesses most commonly multiple, especially in middle cerebral artery distribution; infecting organism(s) depend on source.
  1. 1.
    
    Congenital heart disease: streptococci, Haemophilus spp.
  2. 2.
    
    Endocarditis: S. aureus, viridans streptococci
  3. 3.
    
    Urinary tract: Enterobacteriaceae, Pseudomonadaceae
  4. 4.
    
    Intraabdominal: streptococci, Enterobacteriaceae, anaerobes
  5. 5.
    
    Lung: streptococci, Actinomyces spp., Fusobacterium spp.
  6. 6.
    
    Immunocompromised host: Toxoplasma spp., Enterobacteriaceae, Nocardia spp., listeriosisi, other fungi, tuberculosis
    
    a.
    
    Fungi are responsible for up to 90% of cerebral abscesses in solid organ transplant recipients.
3. C.
  
  Cryptogenic (unknown source): 20% of all brain abscesses

Diagnosis

Differential Diagnosis

•

Other parameningeal infections: subdural empyema, epidural abscess, thrombophlebitis of the major dural venous sinuses and cortical veins
•

Embolic strokes in patients with bacterial endocarditis
•

Mycotic aneurysms with leakage
•

Acute hemorrhagic leukoencephalitis
•

Parasitic infections: toxoplasmosis, echinococcosis, cysticercosis
•

Metastatic or primary brain tumors
•

Cerebral infarction
•

CNS vasculitis
•

Chronic subdural hematoma

Workup

Physical examination, laboratory tests, and imaging studies

Laboratory Tests

•

White blood cell counts are elevated in 60% of patients.
•

Erythrocyte sedimentation rate is usually elevated but may be normal.
•

Lumbar puncture is contraindicated because of the potential for increased intracranial pressure and the risk for herniation due to the space-occupying abscess. Lumbar puncture may be helpful only in those with suspicion for meningitis or abscess rupture into the ventricular system; however, the risk of herniation must be considered.
•

The yield of gram stain and culture of material aspirated at time of surgical drainage is very high.
•

Cultures of contiguous sites of infection should be considered (e.g., paranasal sinus, otitis, skin site abscess from a neurosurgical procedure). These sites of infection may need surgical drainage in order to control the infection.
•

Blood cultures and cerebrospinal fluid cultures may identify the causative organism in up to 25% of patients.

Imaging Studies

•

CT scan with contrast enhancement or MRI with gadolinium can be used to detect brain abscess. CT is rapid and available in most medical settings. An MRI with gadolinium is able to provide more detailed images in order to differentiate between abscess and tumor or other mass.
•

CT scan (Fig. 1) with intravenous contrast enhancement is still an excellent test (sensitivity 95%-99%).

FIG.1

Brain abscess.

This 48-year-old male presented with status epilepticus. Computed tomography (CT) of the brain showed a parietal mass, which at brain biopsy was found to be an abscess. Cultures grew mixed gram-positive and gram-negative organisms and anaerobes. The patient was subsequently found to be human immunodeficiency virus positive. A, Noncontrast head CT, brain windows. B, CT with intravenous (IV) contrast moments later, brain windows. Abscesses and other infectious, inflammatory, or neoplastic lesions typically have surrounding hypodense regions representing vasogenic edema. When IV contrast is administered (B), the lesion may enhance peripherally, often referred to as ring enhancement.

From Broder JS: Diagnostic imaging for the emergency physician, Philadelphia, 2011, Saunders.
•

Serial CT or MRI scanning is recommended to follow the response to therapy.

Treatment

Acute General Rx

•

Effective treatment involves a combination of empiric antibiotic therapy and timely excision or aspiration of the abscess.
•
If evidence of edema or mass effect, treatment of elevated intracranial pressure is paramount.
1. •
  
  Hyperventilation of mechanically ventilated patient.
2. •
  
  Dexamethasone initially in a dosage of 10 mg IV followed by 4 mg IV q6h until symptoms of cerebral edema subside. Steroids should be discontinued as soon as possible.
3. •
  
  Mannitol 0.25 to 1 g/kg IV over 20 to 30 min q6 to 8h; maximum of 6 g/kg in 24 hr.
•

Medical therapy is never a substitute for surgical intervention to relieve increased intracranial pressure. Neurologic deterioration usually mandates surgical intervention.
•

Steroids should be limited to patients with severe cerebral edema or midline shift.

Medical Rx

If abscess <2.5 cm and patient is neurologically stable and conscious, may start antibiotics and observe. Empiric antibiotic therapy guided by:

•

Abscess location
•

Suspicion of primary source
•

Presence of single or multiple abscesses
•

Patient’s underlying medical conditions (e.g., HIV, immunocompromised)

Selection of empiric antibiotic therapy:

•
Primary infection or contiguous source:
1. 1.
  
  Otitis media/mastoiditis, sinusitis: third-generation cephalosporin (cefotaxime 2 g q4h IV or ceftriaxone 2 g q12h IV) plus metronidazole 15 mg/kg IV as a loading dose, then 7.5 mg/kg q8h IV, not to exceed 4 g per day
2. 2.
  
  Dental infection: penicillin G (20 million to 24 million units per day IV in six divided doses) plus metronidazole (dose as above)
3. 3.
  
  Head trauma: third- or fourth-generation cephalosporin (cefotaxime 2 g IV q4h or ceftriaxone 2 g IV q12h or cefepime 2 g IV q8h) plus vancomycin (30 mg/kg IV in two divided doses adjusted for renal function)
4. 4.
  
  Postoperative neurosurgery: vancomycin (dose as above) plus ceftazidime (2 g IV q8h) or cefepime (2 g IV q8h), or meropenem (1 g IV q8h). Replace vancomycin with nafcillin (2g IV q4h) if susceptibility testing reveals methicillin-sensitive Staphylococcus aureus
•

Hematogenous spread (congenital heart disease, endocarditis, urinary tract, lung, intraabdominal): vancomycin (empiric therapy, dose as above) or nafcillin (if susceptibility testing reveals methicillin-sensitive S. aureus, dose as above) plus metronidazole plus third-generation cephalosporin (cefotaxime 2 g IV q4h or ceftriaxone 2 g IV q12h). Antibiotic therapy can be adjusted based on the etiology of the underlying infection, if known. Depending on the source, many experts advocate for anaerobic coverage, even with no documentation given suboptimal sensitivity of current techniques.
•

HIV infected or immunocompromised patient: metronidazole plus a third-generation cephalosporin, antifungal, or antiparasitic agentDuration of antibiotic therapy is guided by the clinical course and by whether the abscess was surgically aspirated or excised; it is usually prolonged. Most recommend parenteral treatment for at least 4 to 8 weeks, with serial neuroimaging to ensure adequate resolution. (Imaging weekly could be considered for first 2 weeks of therapy, then every 2 weeks until resolution.) Surgical therapy may be required for clinical failure (i.e., increasing size of abscess on imaging despite antibiotic therapy).

Surgical Rx

•
Three indications for surgical intervention:
1. 1.
  
  Collect specimens for culture and sensitivity
2. 2.
  
  Reduce mass effect
3. 3.
  
  Clinical failure with antibiotic therapy alone
•

Stereotactic biopsy or aspirate of the abscess if surgically feasible
•

Essential to selection of targeted antimicrobial coverage
•
Timing and choice of surgery depends on:
1. •
  
  Primary infection source
2. •
  
  Number and location of the abscesses
3. •
  
  Whether the procedure is diagnostic or therapeutic
4. •
  
  Neurologic status of the patient

Disposition

•

Prompt diagnostic consideration, early institution of appropriate antimicrobial therapy, and advanced neuroradiologic imaging have reduced the mortality rate from brain abscesses from 40% to 80% in the preantibiotic era to 10% to 20% at present.
•

Morbidity is usually manifest as persistent neurologic sequelae (seizures, intellectual or behavioral impairment, motor deficits).

Referral

Consultation with a neurosurgeon is mandatory.

Pearls & Considerations

Comments

•

It is important to maintain a high index of suspicion because a brain abscess often presents with nonspecific symptoms.
•

Rapid imaging and early institution of appropriate antimicrobial therapy improve patient morbidity and mortality.
•

Neurosurgical consultation is mandatory.

Prevention

Because brain abscesses arise from either contiguous infections or hematogenously from a remote site, early and appropriate treatment of predisposing infections is paramount to prevent brain abscess.

Ferri – Brain Abscess