Brain abscess

Diagnostic workup
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By John E Greenlee MD

Brain abscess should be considered in any patient presenting with recent onset of severe headache or with symptoms or signs of a rapidly developing space-occupying intracranial process. Brain abscess should also be kept in mind in the patient with new onset of focal or generalized seizures. A history of systemic infection, sinusitis, otitis, carious teeth, drug abuse, or risk factors for AIDS should increase diagnostic concern (Fritz and Nelson 1997). Fever is present in only about 50% of patients; even when present, it may be 38°C or less (Kastenbauer et al 2004; Brouwer et al 2014a; Brouwer et al 2014b). The peripheral white blood cell count is normal in 40% of patients and is elevated above 20,000 cells/mm3 in less than 10% of patients (Kastenbauer et al 2004). The erythrocyte sedimentation rate is usually minimally elevated but may be normal (Kastenbauer et al 2004). C-reactive protein levels are frequently elevated and do not correlate with the erythrocyte sedimentation rate (Schliamser et al 1988). Kamra and colleagues have reported 3 patients in whom unsuspected brain abscess with intraventricular rupture presented as meningitis poorly responsive to antibiotic treatment (Kamra et al 2002).

MRI with use of gadolinium enhancement is the diagnostic procedure of choice in suspected brain abscess (Smith 1992; Enzmann 1993; Tunkel et al 2000; Brouwer et al 2014a; Brouwer et al 2014b). Diffusion-weighted MRI or MR spectroscopy may allow differentiation between brain abscess and tumor with central necrosis (Reddy et al 2006; Fertikh et al 2007) and may also help differentiate between bacterial, tuberculous, and fungal abscesses (Kaminogo et al 2002; Luthra et al 2007; Nickerson et al 2012). Typically, brain abscesses will show increased signal on diffusion-weighted images and corresponding hypodensity on apparent diffusion coefficient (ADC) images (Brouwer et al 2014a). Diffusion tensor imaging may also provide a useful adjunctive MRI sequence to differentiate between abscesses and glial or metastatic tumors (Toh et al 2011; Nickerson et al 2012). Limited data also suggest that MRI with diffusion-weighted images may be of value in identifying and following ventricular rupture of abscesses (Rana et al 2002; Engh et al 2008). Contrast-enhanced CT may fail to detect lesions easily discernible on MRI but should be used if MRI is not available (Smith 1992). The sensitivity of contrast-enhanced CT may be increased if the scan is repeated 30 to 60 minutes after contrast infusion (Britt and Enzmann 1983; Enzmann et al 1983). Both MRI and CT will delineate the amount of edema surrounding the abscess and may also document the presence of accompanying sinusitis or otitis (Smith 1992).|{picture:dgba.bmp}{caption:Classic appearance of a brain abscess on MRI}{label:This 49-year-old male was told that he no longer needed SBE prophylaxis for dental procedures despite the presence of his patent foramen ovale. Three weeks after undergoing routine teeth cleaning, this patient developed a seizure. Axial MR imaging of a pathologically proven brain abscess in this patient reveals (A) marked restricted diffusion on diffusion-weighted images, (B) high T2 signal, and (C) FLAIR signal due to edema and a well circumscribed mass in the right frontal lobe. Once the capsule has formed (usually within 2 to 3 weeks), the walls of the mass are often (D) clearly delineated even without on T1 weighted imaging, and (E) the walls show brisk enhancement with contrast and demarcates the wall from the necrotic center. (Contributed by Dr. Diana Gomez-Hassan.)}|

Midazolam HCl (Versed), titrated in 0.5 mg increments to the desired level of sedation, (usually less than 5 mg total dose), may be required to prevent motion artifact in delirious or agitated patients. Careful physician monitoring of respiratory and neurologic status is essential if sedation is employed. Lumbar puncture is contraindicated in brain abscess: spinal fluid abnormalities are usually nonspecific, and the procedure itself is accompanied by a 10% to 18% risk of brain herniation and death (Chun et al 1986). The patient should be evaluated for remote sources of infection with appropriate cultures of blood and other fluids such as sputum, pus from sinuses, or material obtained at myringotomy.

In This Article

Historical note and nomenclature
Clinical manifestations
Clinical vignette
Pathogenesis and pathophysiology
Differential diagnosis
Diagnostic workup
Prognosis and complications
References cited