eMedicine Specialties > Infectious Diseases > CNS Infections

Brain Abscess

Author: Itzhak Brook, MD, MSc, Professor, Department of Pediatrics, Georgetown University School of Medicine
Contributor Information and Disclosures

Updated: Jun 26, 2008

Introduction

Background

Intracranial abscesses are uncommon, serious, life-threatening infections. They include brain abscess and subdural or extradural empyema and are classified according to the anatomical location or the etiologic agent. The term brain abscess is used in this article to represent all types of intracranial abscesses.¹

Intracranial abscesses can originate from infection of contiguous structures (eg, otitis media, dental infection, mastoiditis, sinusitis) secondary to hematogenous spread from a remote site (especially in patients with cyanotic congenital heart disease), after skull trauma or surgery, and, rarely, following meningitis. In at least 15% of cases, no source can be identified.²

In recent years, the complex array of etiologic agents that cause brain abscess has become better understood.

Pathophysiology

Brain abscess is caused by intracranial inflammation with subsequent abscess formation. In at least 15% of cases, the source of the infection is unknown (cryptogenic). Infection may enter the intracranial compartment directly or indirectly via 3 routes.

Contiguous suppurative focus (45-50% of cases)

Direct extension may occur through necrotic areas of osteomyelitis in the posterior wall of the frontal sinus, as well as through the sphenoid and ethmoid sinuses.³ This direct route of intracranial extension is more commonly associated with chronic otitic infection and mastoiditis than with sinusitis.⁴ Odontogenic infections can spread to the intracranial space via direct extension or a hematogenous route. Contiguous spread could extend to various sites in the central nervous system, causing cavernous sinus thrombosis; retrograde meningitis; and epidural, subdural, and brain abscess.

The valveless venous network that interconnects the intracranial venous system and the vasculature of the sinus mucosa provides an alternative route of intracranial bacterial entry. Thrombophlebitis originating in the mucosal veins progressively involves the emissary veins of the skull, the dural venous sinuses, the subdural veins, and, finally, the cerebral veins. By this mode, the subdural space may be selectively infected without contamination of the intermediary structure; a subdural empyema can exist without evidence of extradural infection or osteomyelitis.

Intracranial extension of the infection by the venous route is common in paranasal sinus disease, especially in acute exacerbation of chronic inflammation. Chronic otitis media and mastoiditis generally spread to the inferior temporal lobe and cerebellum, causing frontal or ethmoid sinus infection and dental infection of the frontal lobe.⁵

Trauma (10% of cases)

Trauma that causes an open skull fracture allows organisms to seed directly in the brain. Brain abscess can also occur as a complication of intracranial surgery, foreign body, bullets, and shrapnel.

Hematogenous spread from a distant focus (25% of cases)

These abscesses are more commonly multiple and multiloculated and are frequently found in the distribution of the middle cerebral artery. These infections are associated with cyanotic heart disease, endocarditis, lung infections (eg, abscess, empyema, bronchiectasis), skin infection, abdominal and pelvic infections, neutropenia, transplantation,⁶ esophageal dilatation, injection drug use,⁷ and HIV infection.

Frequency

United States

Before the emergence of the AIDS pandemic, brain abscesses were estimated to account for 1 per 10,000 hospital admissions, or 1500-2500 cases annually.² The prevalence of brain abscess in patients with AIDS is higher, so the overall rate has thus increased.⁸ The frequency of fungal brain abscess has increased because of the frequent administration of broad-spectrum antimicrobials, immunosuppressive agents, and corticosteroids.

International

Brain abscesses are rare in developed countries but are a significant problem in developing countries. The predisposing factors vary in different parts of the world.

Mortality/Morbidity

With the introduction of antimicrobics and the increasing availability of imaging studies, such as CT scanning and MRI, the mortality rate has decreased to less than 5-15%. Rupture of a brain abscess, however, is associated with a high mortality rate (up to 80%).

The frequency of neurological sequelae in persons who survive the infection varies from 20-79% and is predicated on how quickly the diagnosis is reached and antibiotics administered.⁹

Sex

Brain abscesses are more common in males than in females.

Age

Brain abscesses occur more frequently in the first 4 decades of life. Because the main predisposing cause of subdural empyema in young children is bacterial meningitis, a decrease in meningitis due to the Haemophilus influenzae vaccine has reduced the prevalence in young children.

Clinical

History

• In about two thirds of patients, symptoms are present for 2 weeks or less. The clinical course ranges from indolent to fulminant.
• Most symptoms are a result of the size and location of the space-occupying lesion or lesions.
• The triad of fever, headache (often severe and on the side of the abscess), and focal neurologic deficit occurs in less than half of patients. The frequency of common symptoms and signs is as follows:¹
  • Headache - 70%
  • Mental status changes (may indicate cerebral edema) - 65%
  • Focal neurologic deficits - 65%
  • Fever - 50%
  • Seizures - 25-35%
  • Nausea and vomiting - 40%
  • Nuchal rigidity - 25%
  • Papilledema - 25%
• A suddenly worsening headache, followed by emerging signs of meningismus, is often associated with rupture of the abscess.

Physical

• The clinical picture of brain abscess usually manifests as symptoms of a space-occupying lesion. The symptoms and signs include the following:
  • Low- or high-grade fever
  • Persistent headache (often localized)
  • Drowsiness
  • Confusion
  • Stupor
  • General or focal seizures
  • Nausea and vomiting
  • Focal motor or sensory impairments
  • Papilledema
  • Ataxia
  • Hemiparesis
• Localized neurologic signs are eventually found in most patients. The signs and/or symptoms are a direct function of the intracranial location of the abscess.
  • Cerebellar abscess - Nystagmus, ataxia, vomiting, and dysmetria
  • Brainstem abscess - Facial weakness, headache, fever, vomiting, dysphagia, and hemiparesis
  • Frontal abscess - Headache, inattention, drowsiness, mental status deterioration, motor speech disorder, hemiparesis with unilateral motor signs, and grand mal seizures
  • Temporal lobe abscess - Headache, ipsilateral aphasia (if in the dominant hemisphere), and visual defects
• In the initial stages of the infection, an abscess can manifest as a nonspecific form of encephalitis accompanied by signs of increased intracranial pressure.
• Papilledema may develop in older child and adults, and younger infants may exhibit bulging fontanels. This is a late expression of cerebral edema.
• A ruptured brain abscess may produce purulent meningitis associated with signs of neurologic damage.
• Specific clinical symptoms are characteristic of some pathogens.

Causes

• Anaerobic and microaerophilic cocci and gram-negative and gram-positive anaerobic bacilli are the most important isolates. A significant number of brain abscesses are polymicrobic.^10,11,12,13
• The predominant organisms include the following:
  • Staphylococcus aureus
  • Aerobic, anaerobic, and microaerophilic streptococci, including alpha-hemolytic streptococci and Streptococcus milleri
  • Bacteroides, Prevotella, and Fusobacterium species
  • Enterobacteriaceae organisms, including Klebsiella pneumoniae, Escherichia coli , and Proteus species (Rare isolates include Enterobacter species, Actinobacillus actinomycetemcomitans, and Salmonella species.)
  • Pseudomonas species
  • Other anaerobes
• Less common causes include the following:
  • H influenzae
  • Streptococcus pneumoniae
  • Neisseria meningitidis
  • Haemophilus aphrophilus
  • Nocardia asteroides
  • Mycobacterium species
  • Fungi (eg, Aspergillus, Candida, Cryptococcus, Mucorales, Coccidioides, Histoplasma capsulatum, Blastomyces dermatitidis, Bipolaris, Exophiala dermatitidis, Curvularia pallescens, Ochroconis gallopava, Ramichloridium mackenziei)
  • Protozoa (eg, Toxoplasma gondii, Entamoeba histolytica, Trypanosoma cruzi, Schistosoma, Paragonimus)
  • Helminths (eg, Taenia solium)
  • T gondii
  • Pseudallescheria boydii
• The following organisms are associated with certain predisposing conditions:¹⁴
  • Sinus and dental infections - Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (eg, Prevotella, Porphyromonas, Bacteroides), Fusobacterium, S aureus, Enterobacteriaceae¹²
  • Pulmonary infections - Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (eg, Prevotella, Porphyromonas, Bacteroides), Fusobacterium, Actinomyces, Nocardia⁷
  • Congenital heart disease - Aerobic and microaerophilic streptococci, S aureus
  • Penetrating trauma -S aureus, aerobic streptococci, Enterobacteriaceae, Clostridium
  • Transplantation -Aspergillus, Candida, Cryptococcus, Mucorales, Nocardia, T gondii⁶
  • Neutropenia - Aerobic gram-negative bacilli, Aspergillus, Cryptococcus, Coccidioides immitis, Candida, N asteroides, Listeria monocytogenes, Mucorales^15,16
  • HIV infection -T gondii, Mycobacterium, Cryptococcus, Nocardia, L monocytogenes⁸

• Search for CME/CE on This Topic »

• Brain Abscess (Emergency Medicine)
• Brain, Abscess (Radiology)
• Middle Ear, Cholesteatoma (Otolaryngology and Facial Plastic Surgery)
• Facial Trauma, Frontal Sinus Fractures (Plastic Surgery)

• Infections Center
• Brain Infection Symptoms
• Brain and Nervous System Center
• Brain Infection Overview
• Brain Infection Causes
• Brain Infection Treatment
• Antibiotics Introduction

• Management Of Brain Abscess: An Overview
• Molecular Techniques Yield Many More Strains Than Culturing
• Multiple Cranial Nerve Involvement Caused by Brucella melitensis