Evaluation of Brain Abscesses in Children

Interviewing the Patient and the Family

• Failure to thrive: For infants, determine if there are any signs of failure to thrive (i.e., poor growth, lack of appetite, or delay in development) (54).
• Risk factors of infection in history: Recognize any recent or chronic infections, especially of the head, ears, nose, or throat. Ask about any recent dental procedures, head trauma, or neurosurgical or otolaryngology procedure. Determine if there is a history of congenital disease, immune deficiency, and sick contacts (54).
• Signs of infection: Inquire about fevers, headache, nasal or ear drainage, and earache (54).

Examination

• LOC documentation: Note the general appearance of the child. Document whether the child is interactive, lethargic, or irritable.
• Head examination for signs of elevated ICP and otitis: Inspect and palpate the skull for tenderness, trauma, or swelling. Check the ears for drainage, and look at the mouth and throat for exudate, erythema, dental caries, or swelling. Measure head circumference, and note whether the fontanelles are bulging or if the sutures are splayed.
• Meningismus: If the child has concurrent meningitis, you may notice neck stiffness or photophobia.
• Cranial nerve examination for asymmetry: Perform a full cranial nerve examination, looking for asymmetry or dysfunction. In an infant, inspect for reactivity of the pupils and check for conjugate gaze.
• Focal long tract signs: Assess motor strength and sensation in all four extremities.
• Heart auscultation for signs of disease: Auscultate the heart for murmurs, clicks, or dysrhythmias. Observe for clues of right-to-left heart shunting such as cyanosis, clubbing, and tachypnea.

Laboratory Tests

No single routine laboratory or biological study yields findings that are pathognomonic for the diagnosis of brain abscesses in children (30).

• CBC, ESR, and C-reactive protein may be abnormal: Peripheral leukocytosis, an elevated ESR, and elevated C-reactive protein may be found in children with brain abscesses. It is not uncommon, however, for these levels to be normal, even in the setting of a brain abscess (55). ESR may be normal (especially in congenital cyanotic heart disease where polycythemia lowers the ESR) (60).
• Blood cultures rarely positive: Blood cultures are infrequently positive for bacteria, as these results depend on the source of the infection. Regardless,blood cultures should be obtained in all cases prior to antibiotic treatment, given that many abscesses originate from blood-borne bacterial seeding (29).
• CSF analysis nonspecific: Published reports provide a consensus that CSF findings are nonspecific (30). In those cases in which CSF has been obtained, there may be a mild mononuclear pleocytosis, slight elevation of protein, and a normal concentration of glucose; however, the culture tends to be sterile unless the abscess has ruptured into the ventricular system (31).
• Evaluate for mass prior to lumbar puncture: A mass effect associated with brain abscesses is a strong contraindication for lumbar puncture.

Radiologic Tests

Plain x-ray

• Chest x-ray: A chest x-ray (and chest CT scan if indicated) should be obtained to look for a pulmonary source.

CT scan

CT imaging has proved a valuable asset in the diagnosis of brain abscesses. This imaging modality allows localization of the abscess and demonstration of any associated edema or mass effect.

• 95%+ sensitivity but lower specificity: The sensitivity of the CT scan is between 95 and 99%, but the specificity is lower because of the difficulty in differentiating these lesions from other pathological processes such as tumors, cysticercosis, tuberculomas, or some vascular lesions (76, 88, 106, 123).
• Image skull base and sinuses if indicated: If there has been direct invasion from the sinuses or middle ear, the imaging of the head should include these regions (31).
• Ring enhancement surrounding hypodense center: Depending on the stage of the abscess, the lesion typically has a hypodense center with ring enhancement on contrast-enhanced studies.
• Early cerebritis stage: The area is not well defined, and a CT scan may demonstrate normal findings, a hypodense area, or minimal enhancement with contrast addition.

CT scan with contrast of early cerebritis: A cerebral abscess is shown early in its development. A small contrast-enhancing lesion is surrounded by low-density cerebral edema.

• Late cerebritis stage: On CT scans, the early part of this stage is represented by patchy enhancement that develops into an enhancing ring later in the stage.

CT scan with contrast of late cerebritis: Patchy enhancement and surrounding edema are present in the late cerebritis stage. (Courtesy of H Karabagli, MD)

• Early capsule formation stage: On CT scans, a thin-walled capsule will show enhancement with the addition of contrast agent.

CT scan with contrast of young abscess: This cranial CT scan shows a round spherical mass of abscess and edema in right hemisphere. (Courtesy of C Onal, MD)

• Late capsule formation stage: A thickened capsule is represented by a bright, enhancing ring on CT scan.

CT scan with contrast of mature abscess: Thickened capsule formation is represented by a bright, enhancing ring in the late capsule formation stage. (Courtesy of H Karabagli, MD)

MRI

MRI can be used to demonstrate more anatomical detail with superior resolution than CT scanning. Similar to that for a CT scan, this imaging modality’s specificity may be compromised in differentiating abscesses from other lesions with similar imaging characteristics. The advantages of MRI over CT scanning include better differentiation of edema from liquefactive necrosis, greater sensitivity for early satellite lesions, and more sensitivity in the detection of early cerebritis (3, 30).

• Edema more evident early cerebritis: In the early cerebritis stage, peripheral edema can be observed more evidently in MRI studies.
• Ring enhancement develops earlier: In the late cerebritis stage, ring enhancement can be visualized earlier in MRI studies compared with CT scanning.
• T1-weighted MRI hypointense center: Abscesses appear slightly hypointense on T1-weighted images (51). On contrast-enhanced T1-weighted images, the lesion has a hypointense center and ring enhancement (51).

T1-weighted gadolinium-enhanced axial MRI of young abscess: The lesion has a hypointense center and ring enhancement. (Courtesy of H Karabagli, MD)

T1-weighted gadolinium-enhanced axial MRI of mature abscess: Shown is a hypodense lesion with a enhancing ring (abscess capsule) of regular thickness. There is a slight amount of hypodensity anterior to capsule consistent with edema. (Courtesy of H Karabagli, MD)

T1-weighted gadolinium-enhanced coronal MRI of young abscess: Hypodense lesion with an enhancing ring (abscess capsule) of regular thickness is present. (Courtesy of H Karabagli, MD)

T1-weighted gadolinium-enhanced coronal MRI of mature abscess: Shown is the thicker capsule of a more mature abscess. (Courtesy of H Karabagli, MD)

T1-weighted gadolinium-enhanced sagittal MRI of multilobulated abscess: A right subcortical multilocular brain abscess is present with peripheral edema and rim enhancement. (Courtesy of C Onal, MD)

• T2-weighted images have hyperintense center: Abscesses appear hyperintense on T2-weighted images (51).

T2-weighted MRI of brain abscess: The abscess and the surrounding edema appear hyperintense. (Courtesy of H Karabagli, MD)

• FLAIR differentiates CSF from abscess: FLAIR images help to better delineate brain abscesses in the vicinity of CSF-containing spaces, as it suppress the CSF hyperintense signal (92).
• Diffusion-weighted MRI differentiates abscess from tumor: Diffusion-weighted MRI studies aid in the differential diagnosis of other ring-enhancing lesions such as glioblastoma, lymphoma, or metastases and an abscess. In contrast to necrotic or cystic brain tumors that appear hypointense on diffusion-weighted MRI, abscesses appear hyperintense on diffusion-weighted MRI. Diffusion-weighted MRI is especially useful in the early stages of the infectious process and is a very useful modality to aid in early diagnosis and treatment of brain abscesses (18, 35, 48, 63, 89, 107, 124). Restricted diffusion in brain abscesses has been assumed to be a consequence of inflammatory cells, necrotic debris, and the viscosity of the purulent material contained within the abscess; however, it has been shown that viable cell density is the main biological parameter responsible for restricted diffusion in brain abscesses (107).
• MR spectroscopy peaks bacteria specific: MR spectroscopy has been applied to the examination of cerebral abscesses. MR spectroscopy of brain abscesses showed none of the usual detectable resonances from normal brain parenchyma or brain tumor metabolites such as N-acetyl-aspartate, phosphorous creatine, and choline compounds. Instead, the abscesses showed resonances from lactate, acetate (both products of bacterial metabolism) lipids, and amino acids (101).
• Differentiating bacterial from fungal abscess: Diffusion-weighted MRI and MR spectroscopy can be helpful potentially to differentiate between fungal and bacterial sources (113).

Ultrasonography

• Neonate: In the neonate, bedside cranial ultrasonography is an alternative for radiological diagnosis of brain abscess (34).
• Endocarditis: If endocarditis is suspected, an echocardiogram should be obtained (31). An echocardiogram (Doppler and/or echocardiogram with agitated saline injection -bubble study) is used for suspected hematogenous spread, to look for patent foramen ovale or cardiac vegetations (60).

Nuclear Medicine Tests

• Indium-111 labeled leukocytes: In cases in which CT and/or MRI are inconclusive, Indium-111 radiolabeled leukocyte scanning can help clarify the diagnosis. The technique is easy and non-invasive and can provide information that might influence management. The main disadvantage is that optimal images are obtained 24 hours after injection (although positive images are sometimes obtained at 6 hours), and, therefore, this test is best suited to patients who do not require emergent surgery. The diagnostic accuracy has been reported to be approximately 96%, with a sensitivity and specificity of 100% and 94%, respectively (9, 118, 120).
• Thallium-201 SPECT: This test is useful for differentiating lymphoma from toxoplasmosis in AIDS patients. Thallium-201 is taken up by lymphoma but not by toxoplasma abscesses. SPECT thallium may also help differentiate tumor from abscess in non-AIDS patients, although false-positive results have been reported (118).

Electrodiagnostic Tests

• EEG: An EEG can be useful in the management of a patient whose clinical examination is not consistent with the disease process and who may be suffering from subclinical seizures (55).