eMedicine Specialties > Emergency Medicine > Infectious Diseases

Brain Abscess: Differential Diagnoses & Workup

Author: Lisa Elizabeth Thomas, MD, Staff Physician, Harvard Affiliated Emergency Medicine Residency, Brigham and Women's Hospital and Massachusetts General Hospital
Coauthor(s): Joshua N Goldstein, MD, PhD, FAAEM, Assistant Professor of Surgery (Emergency Medicine), Harvard Medical School; Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Sep 25, 2008

Differential Diagnoses

Candidiasis
Meningitis
Catscratch Disease
Metastatic Cancer, Unknown Primary Site
Cavernous Sinus Thrombosis
Mycotic Cerebral Aneurysm
Cryptococcosis
Neoplasms, Brain
Encephalitis
Neoplasms, Spinal Cord
Epidural and Subdural Infections
Neurocysticercosis
Epidural Hematoma
Pediatrics, Febrile Seizures
Headache, Cluster
Retinal Artery Occlusion
Headache, Migraine
Spinal Cord Infections
Headache, Tension
Stroke, Ischemic
HIV Infection and AIDS
Subarachnoid Hemorrhage
Hypertensive Emergencies
Tuberculosis
Intracerebral Hemorrhage

Other Problems to Be Considered

Cerebellopontine angle tumor
Extradural abscess
Pediatric AIDS
Subdural empyema
Cranial osteomyelitis 


Recent evidence suggests that a strong statistical association of pulmonary arteriovenous malformation (PAVM) and brain abscess exists. To date, no evidence of a causal relationship between the two exists, but if a patient is known to have PAVM, an increased level of suspicion should exist for brain abscess if symptoms suggest the diagnosis. Conversely, some have called for screening for PAVM in all patients with brain abscess in order to avoid missing this potentially life-threatening disorder.10

Workup

Laboratory Studies

Laboratory tests are rarely helpful in establishing a diagnosis of brain abscess.2,7

  • Elevated white blood cell (WBC) count or erythrocyte sedimentation rate (ESR) is not reliably found.6,21
  • Blood culture results may only be positive in 30% of patients2,22 but should always be obtained. Hematogenous spread may be the source as noted above, and a positive blood culture result may help guide therapy, especially if empiric antibiotics are started and abscess fluid culture yields no growth.6,2
  • Culture specimen from any other suspected focus of infection should also be collected, as this may also give clues for possible distant sources.11

Imaging Studies

  • CT imaging of the brain (with and without contrast) is the most readily available study for establishing diagnosis of brain abscess in the ED. 
    • Early in the course, abscess appears as a low-density, irregular zone that does not enhance in the presence of intravenous contrast (early cerebritis).
    • Classically, as the disease progresses, a distinctive "ring enhancement" appears on contrast-enhanced CT, as the abscess wall thickens.
    • Rarely, a well-organized abscess wall fails to generate such ring enhancement. Such false-negative results should not have an impact on ED care or disposition; they have more implications for inpatient care, where the timing of surgical intervention may be dictated by response to preliminary intravenous antibiotics and subsequent organization of the abscess wall.23  
  • CT is generally sufficient to make the preliminary diagnosis, which mandates neurosurgical consultation and admission to the hospital.2,3,6
  • However, MRI is increasingly being used for further evaluation.
    • MRI is more sensitive in detecting early cerebritis.2
    • Posterior fossa lesions may not be identified on CT scan and may require MRI to make the critical diagnosis.2,4
    • A ring-enhancing lesion on CT scan may give rise to a differential diagnosis including abscess versus primary tumor or metastasis. Gadolinium-enhanced MRI is helpful in characterizing these lesions. On diffusion-weighted imaging, pyogenic abscesses have a hyperintense signal, whereas nonpyogenic lesions will have a hypointense or mixed signal. Although not readily available in the emergency department, proton magnetic resonance spectroscopy may also be used to differentiate abscesses.24,25

See Brain, Abscess for images.

Other Tests

  • Ultrasonography: As ultrasonography is becoming widely used in the emergency department, bedside ocular ultrasonography may be performed to assess for increased intracranial pressure.26

Procedures

  • Lumbar puncture (LP)
    • LP results are generally not helpful in the diagnosis of brain abscess. Performing this procedure in the emergency department is generally indicated only in cases highly suspicious for bacterial meningitis, with a careful balance between any potential change in management and the risk of CNS herniation.4,11
    • The suspicion of brain abscess, presence of any focal neurologic finding, or of papilledema is an absolute indication for CT imaging prior to LP.27
  • In cases where LP had been performed, the findings were nonspecific and cultures were rarely positive.2
  • Abscess aspiration: Culture of the abscess fluid is the most important microbiological study to ensure appropriate targeted therapy. As a result, urgent or emergent neurosurgical consultation is necessary.2,3

More on Brain Abscess

Overview: Brain Abscess
Differential Diagnoses & Workup: Brain Abscess
Treatment & Medication: Brain Abscess
Follow-up: Brain Abscess
References
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References

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Further Reading

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Keywords

brain abscess, intracranial abscess, intracerebral abscess, cerebritis, cerebral abscess

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Contributor Information and Disclosures

Author

Lisa Elizabeth Thomas, MD, Staff Physician, Harvard Affiliated Emergency Medicine Residency, Brigham and Women's Hospital and Massachusetts General Hospital
Lisa Elizabeth Thomas, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, and Phi Beta Kappa
Disclosure: Nothing to disclose.

Coauthor(s)

Joshua N Goldstein, MD, PhD, FAAEM, Assistant Professor of Surgery (Emergency Medicine), Harvard Medical School; Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital
Joshua N Goldstein, MD, PhD, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Stroke Association, and Society for Academic Emergency Medicine
Disclosure: CSL Behring Consulting fee Consulting; Genentech Consulting fee Consulting

Medical Editor

Edward Bessman, MD, Chairman, Department of Emergency Medicine, John Hopkins Bayview Medical Center; Assistant Professor, Department of Emergency Medicine, Johns Hopkins University
Edward Bessman, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Barry J Sheridan, DO, Chief, Department of Emergency Medical Services, Brooke Army Medical Center
Barry J Sheridan, DO is a member of the following medical societies: American Academy of Emergency Medicine
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Jonathan Adler, MD, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital; Division of Emergency Medicine, Harvard Medical School
Jonathan Adler, MD is a member of the following medical societies: American Academy of Emergency Medicine and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

 
 
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