Brain abscess

I. What every physician needs to know.

A brain abscess is an infection in the brain parenchyma that begins as a localized area of cerebritis and develops into a collection of purulent material surrounded by a well-vascularized capsule. Abscesses can be caused by bacteria, fungi or parasites. Solitary or multiple abscesses can be present. Most brain abscesses are due to spread from infection elsewhere in the body. Infection can directly spread, such as in cases of otitis media, mastoiditis and sinus infection. This contiguous spread explains half of the cases. One-third of cases are from hematogenous spread, with endocarditis and pulmonary infections being the most common sources. Endocarditis can lead to multiple abscesses in the brain and in other organs. Approximately 10% of cases are due to penetrating head injury or surgical procedures. Sometimes the mechanism or source is unknown (cryptogenic brain abscess).

Brain abscess can be categorized into four stages:

  • Early cerebritis (days 1-3): inflammatory cells infiltrate, marked perivascular inflammation. Edema develops.

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  • Late cerebritis (days 4-9): necrosis becomes better defined. Vasogenic edema progresses. Fibroblasts begin to organize into a capsule and neovascularity appears.

  • Early capsule formation (days 10-14): capsule becomes thickened, Fibroblasts and macrophages increase. Necrotic core slightly decreases in size.

  • Late capsule formation (more than 14 days): Capsule is dense. Vasogenic edema is reduced.

The source of the infection leads to determination of likely infectious agents. Streptococci are the most commonly cultured bacteria in patients with brain abscess. Brain abscess due to contiguous spread from parameningeal foci is frequently caused by Streptococcus species but staphylococcal and polymicrobial abscesses (including anaerobes such as Bacteroides or Propionibacterium and gram-negative rods such as Escherichia coli) also occur. Multiple bacteria are often found when brain abscesses result from sinus or dental infection and it is estimated that 14-28% of brain abscesses are polymicrobial. Staphylococcus and Streptococcus species are often identified in brain abscesses from hematogenous spread. After penetrating trauma or neurosurgery, infection is usually caused by Staphylococcus aureus, Staphylococcus epidermidis, or gram-negative rods, including Pseudomonas aeruginosa. Cryptococcus, Candida, agents of mucormycosis and Aspergillus are fungi that are associated with abscess, particularly in immunocompromised patients. Mycobacterium tuberculosis, Toxoplasma gondii and Nocardia species are also associated with immunocompromised states.

II. Diagnostic Confirmation: Are you sure your patient has a brain abscess?

A combination of imaging, clinical and laboratory findings confirm the diagnosis.

A. History Part I: Pattern Recognition:

On average, patients have symptoms 11 to 12 days prior to presentation to the hospital. Signs and symptoms on presentation include the following:

  • Headache: 55-70% (the most common clinical manifestation)

  • Fever: variable from study to study. Several studies have less than 50% of patients presenting with fever.

  • Altered consciousness: 48%

  • Hemiparesis: 48%

  • Nausea and vomiting: 32%

  • Seizure: 13-35%

  • Nuchal rigidity: 29%

  • Dysarthria: 20%

  • Sepsis: 17%

  • Visual disturbance: 15%

  • Movement disorders: rare, but are associated with toxoplasmosis.

  • Papilledema: rare, associated with increased intracranial pressure.

Sudden worsening of the headache, accompanied by a new onset of meningismus, may signify rupture of the abscess into the ventricular space.

B. History Part 2: Prevalence:

  • Estimated incidence of 0.3 to 1.3 per 100,000 people per year. This rate is increased in immunocompromised patients.

  • More common in males than females (1.3:1 to 3:1)

  • 1-2% of intracranial mass lesions

Primary infectious locations/predisposing conditions
  • Sinus infection

  • Otitis media

  • Dental infection

  • Mastoiditis

  • Cardiac

    Infective endocarditis

    Tetralogy of Fallot

    Patent foramen ovale

    Cyanotic heart disease

  • Neurosurgical procedures

  • Immunosuppression

  • Head injury; penetrating and non-penetrating

  • Pulmonary arteriovenous fistula, bronchiectasis

  • Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)

  • Unknown

C. History Part 3: Competing diagnoses that can mimic brain abscess.

  • Other infectious processes (imaging will help differentiate)


    Viral encephalitis

    Subdural empyema


  • Inflammatory processes

    Multiple sclerosis

    Neuromyelitis optica

    Differentiating factors:

    Cultures are negative

    Can have positive oligoclonal bands and immunoglobulin G (IgG) index

    Patients usually have previous events (numbness, tingling, weakness, visual loss, etc.) that can be elicited by a thorough history

    No fever

  • Malignancy



    Differentiating factors:

    Negative cultures

    Positive flow cytometry or cytology

    B-type symptoms

    Duration is generally longer prior to presentation

  • Intraparenchymal hematoma

    Resolving hematomas can have a similar appearance on magnetic resonance imaging (MRI)

    Differentiating factors:

    Negative cultures

    Neuroimaging features change with time consistent with intraparenchymal hematoma

    History of risk factors for intraparenchymal hematoma

  • Contusion

    Differentiating factors:

    Negative cultures

    History of trauma

  • Ischemia

    Subacute ischemia can have contrast enhancement, but not in the same pattern. Restricted diffusion may or may not be present.

  • Radiation necrosis

    Differentiating factors:

    Negative cultures

    History of radiation

D. Physical Examination Findings.

Neurological findings are dependent upon the location and size of the lesion. In some cases, consciousness can be mildly impaired and no focal deficits can be ascertained.

  • Frontal lobe: poor attention, decline in cognitive abilities, hemiparesis, and seizures.

  • Temporal lobe: aphasia, visual field deficits, hemiparesis or sensory deficits, particularly in the face.

  • Parietal lobe: findings can be subtle, but can include neglect and apraxia.

  • Occipital lobe: homonymous hemianopia.

  • Cerebellar: ataxia, nystagmus, spasticity, and increased reflexes. Impaired consciousness due to compression of fourth ventricle leading to hydrocephalus can occur.

  • Basal ganglia: movement disorders (hemiballismus, etc.).

  • Multiple lesions: difficult to localize physical examination signs.

E. What diagnostic tests should be performed?

The physical examination findings in brain abscess can be highly varied and are dependent upon the size and location of the abscess. A search for the source of the lesion should be performed during the physical examination.

  • Full neurological examination

    Focal findings can help localize the lesion, but focal findings may not be present in all cases.

  • Fundoscopic examination

    Evaluate for papilledema and Roth spots

  • Otoscopic examination: fluid levels; appearance of tympanic membrane can help diagnose otitis media.

  • General examination

    Evaluate periphery for Janeway lesions

    Heart murmur can also help identify endocarditis

  • Dental examination: The initial examination does not need to be performed by a dentist; a thorough visual inspection can be performed. If strong suspicion remains for a dental source and initial examination is negative, then a referral to dentistry would be appropriate.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

  • Complete blood count (CBC): elevated white count.

  • Blood cultures: positive in approximately 10% of cases.

  • Lumbar puncture: Prior to performing the procedure, perform imaging to ensure that vasogenic edema has not caused significant mass effect, and risk of herniation is low. Positive in 10-30% of cases. Cerebrospinal fluid (CSF) can be normal if abscess is localized. Intracranial pressure is usually 20 to 300 millimeters mercury (mmHg). White cell count is usually elevated in brain abscess. Cell count ranges from 0 to 100,000 cells per microliter. Differential can help determine if the cause is more likely to be from bacterial or fungal sources. If glucose is low, indicative of infectious process but is generally normal.

  • Cytology and flow cytometry: helps to differentiate infection from malignancy.

  • Erythrocyte sedimentation rate/C-reactive protein (ESR/CRP): non-specific, but likely to be elevated in cases of brain abscess. CRP is more likely to be elevated than ESR.

  • Human immunodeficiency virus (HIV): CD4 (cluster of differentiation 4) count in known HIV-positive individuals.

  • Any material obtained from a neurosurgical procedure should be sent to the laboratory for pathological evaluation and cultures (aerobic, anaerobic, mycobacterial, fungal).

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

  • Brain imaging is essential to the work-up of a patient with a suspected brain abscess. Computed tomography (CT) and/or MRI with contrast should be performed. MRI is preferred.

    CT shows enhancement of capsule. Hypodensity surrounding the capsule indicates edema.


    T1 weighted images with contrast also show enhancement of capsule. May show a characteristic “ring-enhancing lesion”. Hypointensity is present in the necrotic core. Figure 1 is a typical “ring enhancing lesion” in a HIV-positive patient with toxoplasmosis. Figure 2 is an irregularly shaped capsule with enhancement in an immunosuppressed patient with Listeria abscess.

    T2 and fluid-attenuated inversion recovery (FLAIR) images show hyperintense vasogenic edema with hypointense capsule. Figure 3 shows FLAIR imaging in the HIV-positive patient with toxoplasmosis.

    Diffusion weighted images (DWI) and apparent diffusion coefficient (ADC) images are compared to help differentiate abscess from malignancy. Abscess usually has restricted diffusion (brightness on DWI with correlating dark area on ADC). Figure 4 shows a central area of restricted diffusion in the patient with Listeria abscess.

  • Chest X-ray: evaluation of pulmonary causes.

  • Echocardiogram: performed to evaluate for endocarditis.

    If a strong suspicion for endocarditis remains after a negative transthoracic echocardiogram, then consider a transesophageal echocardiogram.

Figure 1.

T1 with contrast in a patient with toxoplasmosis

Figure 2.

T1 with contrast. Atypical appearance of abscess in immunocompromised patient. Listeria was determined to be cause of abscess after contaminated cantelope ingestion.

Figure 3.

T2 FLAIR image in a HIV positive patient with toxoplasmosis

Figure 4.

Central area of restricted diffusion on DWI (left) and ADC (right) images. Immunocompromised patient with multiple listeria abscesses.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.


III. Default Management.

Management of brain abscess hinges upon correct antimicrobial treatment. Consultation with an infectious disease specialist is recommended.

  • Empiric treatment with third- or fourth-generation cephalosporin, vancomycin and metronidazole is recommended until a source or organism can be identified.

  • If contiguous spread from parameningeal foci (otitis media, mastoiditis, sinusitis): ceftriaxone plus metronidazole. Vancomycin should be added if staphylococcal infection suspected.

  • History of penetrating trauma or neurosurgery: vancomycin plus third or fourth-generation cephalosporin with anti-pseudomonal activity (e.g. cefepime) plus metronidazole.

  • Treatment in HIV-positive patients should cover toxoplasmosis. Pyrimethamine and sulfadiazine combination is a first line option for toxoplasmosis.

  • Listeria abscess in immunocompromised patients should be considered. Ampicillin is the treatment of choice.

  • Once the infecting pathogen has been determined, antimicrobial agents can be modified to achieve the most effective therapy. However, if the infection spread from a contiguous site, broad spectrum antimicrobial therapy (including anaerobes) is recommended even if a single organism is recovered in cultures.

Surgical management involves the following:

  • Abscess aspiration can help to determine pathogen and to reduce the size of the abscess. With modern stereotactic neurosurgical techniques, brain abscesses measuring at least 1 centimeter (cm) in diameter are amenable to stereotactic aspiration.

  • An abscess size of 2.5 cm in diameter has been recommended as an indication for neurosurgical intervention.

  • If there is brain shift, with risk of brain herniation, neurosurgical intervention is indicated regardless of abscess size.

  • In patients with multiple abscesses, the largest abscess should be aspirated for diagnostic purposes.

  • Total resection has a limited role these days but if is considered when abscess is superficial and not located in eloquent brain tissue and when there is suspicion of fungal or tuberculous infection or of branching bacteria (Actinomyces or Nocardia).

  • If edema is present causing hydrocephalus, shunting may be necessary.

Vasogenic edema may need to be treated if it is causing mass effect:

  • High dose corticosteroids, such as dexamethasone, can be tapered over the course of several days.

  • If edema is severe and causing significant mass effect, mannitol or hypertonic saline can be considered.

Seizure management involves the following:

  • Patients with seizures should be placed on an antiepileptic. Phenytoin is a common choice due to ease of administration and ability to check levels. Levetiracetam has become popular due to minimal drug interactions and a more favorable side effect profile. Physicians should be aware that despite frequent use of levetiracetam as monotherapy, Food and Drug Administration (FDA) approval is for adjunct therapy. Prophylactic antiepileptic drugs in patients with brain abscess are not routinely indicated.

A. Immediate management.

Antibiotics should be initiated as soon as possible. If mass effect is present, consider corticosteroids. It is unusual to require an emergent neurosurgical procedure for abscess, but a consultation should be considered if the patient has severe mass effect, is comatose, stuporous or has a capsule larger than 2 cm.

B. Physical Examination Tips to Guide Management.

The neurological checks should be performed frequently by nursing, at least every 4 hours after admission. Daily examinations should include a complete neurological examination to evaluate for progression of symptoms, and should specifically be focused on symptoms that localize near the lesion. For example, if a patient has an occipital lesion, visual fields should be performed daily. If progression of symptoms occurs, such as progression of a quadrantanopia to homonymous hemianopia, repeat imaging should be performed.

C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

Drug levels of antibiotics should be monitored when appropriate (i.e. vancomycin).

Kidney function (creatinine) should be evaluated in patients on vancomycin.

If phenytoin is used, levels should be drawn daily until a clear therapeutic steady state is achieved. Liver profiles should be checked at the onset of therapy, and approximately weekly while the patient is admitted. If liver panels are not elevated in subsequent lab draws, then infrequent intermittent checks should be performed.

D. Long-term management.

The length of intravenous antibiotic course is dependent upon the organism(s) found, but is typically 6 to 8 weeks. This is often followed by oral antimicrobial therapy for 2 to 3 months if an appropriate agent is available although the efficacy of this approach has not been established. It is important to continue antibiotic therapy until resolution of the abscess by neuroimaging. Of note, prolonged therapy with metronidazole can lead to peripheral neuropathy.

Other consultations may be necessary, such as with oncology in a patient with cancer, or cardiology in a patient with endocarditis. In patients with immunocompromised states, careful coordination with consultants is required to ensure that medications are managed appropriately.

Discontinuation of antiepileptics is controversial. Some patients require life-long treatment and others can tolerate discontinuation of anti-epileptics if they have been seizure free for more than 2 years. A consultation with a neurologist is recommended.

CT scans or MRI should be obtained to evaluate response to treatment. A repeat scan should be considered within 2 weeks of starting treatment; a scan should be obtained earlier if the patient is not responding to the therapy or develops new symptoms. When discontinuation of antibiotics is reasonable, MRI should be obtained to evaluate for resolution of the abscess. If the abscess enlarges after 2 weeks of antimicrobial therapy, or fails to resolve after 3-4 weeks, further surgical aspiration or excision should be considered.

The combination of surgical aspiration or removal of all abscesses larger than 2.5 cm in diameter, a 6-week or longer course of intravenous antibiotic therapy, and neuroimaging follow-up until resolution provides the best chances for cure.

E. Common Pitfalls and Side-Effects of Management

Due to the non-specific symptoms that may accompany brain abscess, the diagnosis may be delayed.

Antibiotics should be instituted as soon as possible. An aggressive work-up for a primary source of infection is necessary. Antibiotics should be tailored to the source when possible to reduce adverse effects. Antibiotics can be started prior to a lumbar puncture or neurosurgical procedure if these get delayed.

Patients with intracranial abscess should be monitored closely for progression of disease. Abscess rupture is an uncommon complication, but should be on the differential if a patient worsens. Ventriculitis and diffuse spread of bacteria are associated with worse outcomes.

IV. Management with Co-Morbidities


A. Renal Insufficiency.

Dose reduction of antibiotics may be necessary.

Renally cleared antiepileptics (levetiracetam, topiramate, etc.) may require dose reduction.

B. Liver Insufficiency.

Drug levels of antiepileptics metabolized by the liver (phenytoin, valproate) should be monitored. Liver function tests to ensure the values remain stable should be performed.

C. Systolic and Diastolic Heart Failure

Patients with brain abscess are frequently dehydrated due to poor intake, nausea and vomiting. Careful replacement of fluids should occur in patients with heart failure.

D. Coronary Artery Disease or Peripheral Vascular Disease

No change in standard management.

E. Diabetes or other Endocrine issues

No change in standard management.

F. Malignancy

In patients with malignancy, a discussion should occur with the treating oncologist to determine an appropriate treatment plan. Frequently, chemotherapeutics and radiation treatments will be suspended during the treatment for brain abscess. A conversation with the patient and the family regarding the consequences of deferment of treatment should occur. In some cases, goals of care should be clearly established due to the consequences of holding cancer treatment and neurological sequelae that can occur after abscess treatment is complete.

G. Immunosuppression (HIV, chronic steroids, etc.).

Patients on immunosuppression for chronic diseases should consider a suspension of the immunosuppressant. Coordination with the treating physician or a consultant should occur. Several medications, such as azathioprine, will continue to cause immunosuppression for a substantial amount of time after discontinuation of the medication. Unusual causes of brain abscess (listeriosis, toxoplasmosis, etc.) should be considered, and antibiotics tailored appropriately.

In patients with HIV with positive Toxoplasma IgG, low CD4 count and brain imaging suspicious for abscess, treatment for toxoplasmosis should be started.

H. Primary Lung Disease (COPD, Asthma, ILD)

No change in standard management.

I. Gastrointestinal or Nutrition Issues

No change in standard management.

J. Hematologic or Coagulation Issues

If endocarditis is a likely source of brain abscess, then vascular imaging should be considered. Mycotic aneurysms can be identified on a CT angiogram or magnetic resonance angiogram (MRA). Mycotic aneurysms have a risk of rupture with anticoagulation. The risk-benefit ratio must be obtained in patients found to have a brain abscess and an indication for anticoagulation.

K. Dementia or Psychiatric Illness/Treatment

No change in standard management.

V. Transitions of Care

A. Sign-out considerations While Hospitalized.

If the patient experiences focal neurological change, a CT scan should be immediately obtained to evaluate for mass effect. Contrast could be considered if rupture of the abscess is possible. Signs of rupture include severe headache, neck stiffness and altered mental status.

Fever despite tailored antibiotics to the source of the infection should be further evaluated with chest x-ray, blood cultures, urinalysis, and testing for Clostridium difficile if diarrhea is present. Broadening the antibiotic regimen may be necessary if it is believed that the fever originated from the abscess and is possibly improperly covered by the current antibiotic regimen.

Antiepileptics should be started immediately in any patient who develops a seizure. Phenytoin can be loaded at 20 milligrams/kilogram (mg/kg), maintained with 5mg/kg (divided into twice a day dosing if greater than 300mg per dose) and monitored with daily levels until a steady state is achieved. It may be necessary to monitor free levels in patients with low albumin.

B. Anticipated Length of Stay.

Length of stay is variable and is highly dependent upon severity of disease.

C. When is the Patient Ready for Discharge.

The patient is ready for discharge once the appropriate antibiotics have been chosen and the patient is improving. Fever should be resolved, and symptomatic management should properly treat headache, nausea and vomiting.

D. Arranging for Clinic Follow-up

1. When should clinic follow up be arranged and with whom.

  • Primary care physician: within 1-2 weeks after discharge.

  • Infectious disease: within 4-6 weeks after discharge and thereafter until discontinuation of antibiotics.

  • Neurosurgery: within 1-2 weeks.

  • Neurology (if seizures or focal neurological deficits): within 6-8 weeks.

  • Other specialists as indicated by the patient’s course (oncology, cardiology, etc.).

2. What tests should be conducted prior to discharge to enable best clinic first visit.


3. What tests should be ordered as an outpatient prior to, or on the day of, the clinic visit.

CT or MRI with contrast to ensure resolution of abscess.

E. Placement Considerations.

Frequently, patients with brain abscess will require rehabilitation. Most patients require acute or sub-acute rehabilitation. Rehabilitation specialties (physical, occupational and speech therapy) should be consulted early during the hospitalization. A physical medicine and rehabilitation physician can help to determine when the patient is stable for transfer to these facilities based upon progress with therapy. This consultation should occur a few days prior to the anticipated discharge.

A peripherally inserted central catheter (PICC) line should be placed in all patients requiring an outpatient course of intravenous antibiotics.

F. Prognosis and Patient Counseling.

Mortality due to brain abscess is approximately 15%. In subgroups, such as those with immunosuppression after transplantation, deep or brainstem abscess, mortality can be as high as 80%. Residual neurological deficits can be found in 30 to 55% of patients. Severe neurological deficits can be present in 18%. Seizures usually occur within the first year after diagnosis of brain abscess.

VI. Patient Safety and Quality Measures

A. Core Indicator Standards and Documentation.


B. Appropriate Prophylaxis and Other Measures to Prevent Readmission.

  • Deep vein thrombosis (DVT) prophylaxis

  • Gastrointestinal (GI) prophylaxis with a proton pump inhibitor if steroids are used. Blood sugar monitoring and an insulin sliding scale can also be considered with steroid use.

  • If HIV-positive and low CD4, immune reconstitution with combined antiretroviral therapy is recommended.

VII. What's the evidence?

Goldman, L, Schafer, AI. “”. 24th ed.. 2011.

Lu, CH, Chang, WN, Lui, CC. “Strategies for the Management of Bacterial Brain Abscess”. . vol. 13. 2006. pp. 979-985.

Muzumdar, D, Jhawar, S, Goel, A. “Brain Abscess: An Overview”. . vol. 9. 2011. pp. 136-144.

Ropper, AH, Samuels, MA. “”. 2009.

Scheld, SM, Witley, RJ, Marra, CM. “”. 2004.

Brouwer, M, Tunkel, A, McKhann, G, van de Beek, D. “Brain abscess”. . vol. 371. 2014. pp. 447-456.

Tunkel. “Brain abscess”. . 2015.

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