Brain Abscess Workup

Updated: Mar 02, 2021
  • Author: Itzhak Brook, MD, MSc; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Workup

Laboratory Studies

Routine tests

Routine tests in patients with brain abscess include the following:

  • CBC count with differential and platelet count

  • Erythrocyte sedimentation rate (ESR; elevated in up to two thirds of patients)

  • Serum C-reactive protein (CRP) or Westergren sedimentation rate

  • Serological tests for some pathogens (eg, serum immunoglobulin G antibodies, CSF polymerase chain reaction [PCR] for Toxoplasma)

  • Blood cultures for aerobic and anerobic bacteria (at least 2; preferably before antibiotic usage)

  • Moderate leukocytosis is present, and the ESR and CRP level are generally elevated. Serum sodium levels may be low because of inappropriate antidiuretic hormone production. Platelet counts may be high or low.

Cerebrospinal fluid  [40]

A lumbar puncture is rarely warranted and is contraindicated if increased intracranial pressure is present because of the potential for CNS herniation and death. The results are usually unrewarding, consisting of an elevated protein level, pleocytosis with variable neutrophil count, a normal glucose level, and sterile cultures. A lumbar puncture is mostly of value to rule out other disease processes, especially bacterial meningitis. CT imaging or MRI scanning prior to lumbar puncture is absolutely indicated upon the presence of any focal neurologic finding or papilledema. [41]

The white blood cell count is generally high. It reaches 100,000/µL or higher when the abscess ruptures into the ventricle. Many red blood cells are generally observed at that time, and the CSF lactic acid level is then elevated to more than 500 mg. [42]

Abscess aspirate (obtained via stereotactic CT or surgery)  [2]

Culture aspirates of abscesses for aerobic, anaerobic, and acid-fast organisms and fungi

Gram stain, acid-fast stain (for Mycobacterium), modified acid-fast stain (for Nocardia), and special fungal stains (eg, methenamine silver, mucicarmine)

Serology anti-anticysticercal antibodies for the diagnosis of neurocysticercosis

Histopathological examination of the brain tissue

16S Ribosomal sequencing - Several studies using 16S ribosomal DNA polymerase chain reaction amplification increased the number of bacterial species recovered from brain abscesses as compared with standard culture. [39, 43]

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Imaging Studies

CT scanning has made other tests, such as angiography, ventriculography, pneumoencephalography, and radionuclide brain scanning, almost obsolete in the workup of brain abscess. CT is not as sensitive as MRI but is easier to perform.

CT scanning, preferably with contrast administration, provides a rapid means of detecting the size, the number, and the location of abscesses, and it has become the mainstay of diagnosis and follow-up care. This method is used to confirm the diagnosis, to localize the lesion, and to monitor the progression after treatment. However, CT scan results can lag behind clinical findings. [44, 45]  

After the injection of a contrast material, CT scans characteristically show the brain abscess as a hypodense center with a peripheral uniform enhancement ring. Rarely, a well-organized abscess wall fails to generate such ring enhancement.

In the earlier cerebritis stages, CT scans show nodular enhancement with areas of low attenuation without enhancement. As the abscess forms, contrast enhancement is observed. After encapsulation, the contrast material cannot help differentiate the clear center and the CT scan is similar in appearance to those obtained during the early cerebritis stage.

CT scan of a brain abscess. CT scan of a brain abscess.

Many authorities consider MRI to be the first diagnostic method in the diagnosis of brain abscess. It allows for accurate diagnosis and excellent follow-up of the lesions because of its superior sensitivity and specificity. Compared with CT scanning, MRI offers a better ability to detect cerebritis, greater contrast between cerebral edema and the brain, better visualization of the brainstem, and earlier detection of satellite lesions and the spread of inflammation into the ventricles and subarachnoid space.

MRI of a brain abscess. MRI of a brain abscess.

Contrast enhancement with gadolinium diethylenetriaminepentaacetic acid (a paramagnetic agent) helps differentiate the abscess, the enhancement ring, and the cerebral edema around the abscess. T1-weighted images enhance the abscess capsule, and T2-weighted images can demonstrate the edema zone around the abscess. [46]

Diffusion-weighted (magnetic resonance) imaging (DWI) can be used to differentiate between ring-enhancing lesions caused by brain abscess (hypertensive on DWI) from a malignant lesion (hypotensive on DWI). [47]

Susceptibility-weighted phase imaging showed evidence of paramagnetic substances in agreement with the presence of free radicals from phagocytosis in a study of 14 patients with brain abscesses. [48] This technique may provide additional information that is valuable in the characterization of pyogenic brain abscesses.

Since the advent of CT scanning and MRI, the case-fatality rate has decreased by 90%.

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Other Tests

ECG occasionally reveals a focus of high voltage with slow activity. It is nonspecific and rarely of value in confirming a diagnosis of brain abscess. This is the least accurate procedure in the diagnostic evaluation.

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Procedures

Biopsy of cerebral lesion: Hyphae and type of branching can assist in ion diagnosis of specific fungal infections. In patients with toxoplasmosis, special immunochemical tests can be used to detect the organism or its antigens. A brain-touch technique using immunofluorescence monoclonal antibodies against the organism can also provide rapid diagnosis.

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Staging

The early stage of brain abscess (first 7-14 days) is called cerebritis and is associated with edema. Necrosis and liquefaction occur after 2-3 weeks, and the lesion becomes gradually surrounded by a fibrotic capsule. [49]

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