Brain Abscess

A brain abscess can result from

The bacteria involved are usually anaerobic and sometimes mixed, often including anaerobes, such as Bacteroides and anaerobic and microaerophilic streptococci Streptococcal Infections Streptococci are gram-positive aerobic organisms that cause many disorders, including pharyngitis, pneumonia, wound and skin infections, sepsis, and endocarditis. Symptoms vary with the organ... read more . Staphylococci Staphylococcal Infections Staphylococci are gram-positive aerobic organisms. Staphylococcus aureus is the most pathogenic; it typically causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis... read more are commonly involved after cranial trauma, neurosurgery, or endocarditis. Enterobacteriaceae may be isolated in chronic ear infections. After chronic suppurative otitis media Otitis Media (Chronic Suppurative) Chronic suppurative otitis media is a persistent, chronically draining (> 6 weeks), suppurative perforation of the tympanic membrane. Symptoms include painless otorrhea with conductive hearing... read more , anaerobic bacteria, streptococci, and gram-negative bacteria are common causes.

Fungi (eg, Aspergillus Aspergillosis Aspergillosis is an opportunistic infection that usually affects the lower respiratory tract and is caused by inhaling spores of the filamentous fungus Aspergillus, commonly present in... read more ) and protozoa (eg, Toxoplasma gondii Toxoplasmosis Toxoplasmosis is infection with Toxoplasma gondii. Symptoms range from none to benign lymphadenopathy, a mononucleosis-like illness, to life-threatening central nervous system (CNS) disease... read more , particularly in HIV-infected patients) can cause abscesses.

Symptoms result from increased intracranial pressure, mass effect, and sometimes focal brain injury. Classically, headache, nausea, vomiting, lethargy, seizures, personality changes, papilledema, and focal neurologic deficits develop over days to weeks; however, in some patients, these manifestations are subtle or absent until late in the clinical course.

Fever, chills, and leukocytosis may develop before the infection is encapsulated, but they may be absent at presentation, subside over time, or not develop.

When symptoms suggest an abscess, contrast-enhanced MRI with diffusion-weighted images or, if MRI is unavailable, contrast-enhanced CT is done. A fully developed abscess appears as an edematous mass with ring enhancement, which may be difficult to distinguish from a brain tumor Diagnosis Intracranial tumors may involve the brain or other structures (eg, cranial nerves, meninges). The tumors usually develop during early or middle adulthood but may develop at any age; they are... read more or occasionally infarction Diagnosis Ischemic stroke is sudden neurologic deficits that result from focal cerebral ischemia associated with permanent brain infarction (eg, positive results on diffusion-weighted MRI). Common causes... read more ; CT-guided aspiration, culture, surgical excision, or a combination may be necessary.

Culturing pus aspirated from the abscess can make targeted antibiotic therapy of the abscess possible. However, antibiotics should not be withheld until culture results are available.

Lumbar puncture is not done because it may precipitate transtentorial herniation and because cerebrospinal fluid (CSF) findings are nonspecific (see table Cerebrospinal Fluid Abnormalities in Various Disorders Cerebrospinal Fluid Abnormalities in Various Disorders ).

All patients receive antibiotics for a minimum of 4 to 8 weeks. Initial empiric antibiotics include one of the following:

Both are effective against streptococci, Enterobacteriaceae, and most anaerobes but not against Bacteroides fragilis. If clinicians suspect Bacteroides species (as in chronic sinusitis or otitis), metronidazole 15 mg/kg (loading dose) followed by 7.5 mg/kg IV every 6 hours is also required. If S. aureus is suspected (eg, after cranial trauma or neurosurgery or in endocarditis), vancomycin 1 g every 12 hours is used (with cefotaxime or ceftriaxone) until sensitivity to nafcillin (2 g every 4 hours) is determined. Response to antibiotics is best monitored by serial MRI or CT.

Drainage (CT-guided stereotactic or open) provides optimal therapy and is necessary for most abscesses that are solitary and surgically accessible, particularly those > 2 cm in diameter. If abscesses are < 2 cm in diameter, antibiotics alone may be tried, but abscesses must then be monitored with frequent serial MRI or CT (initially as often as every 2 to 3 days); if abscesses enlarge after being treated with antibiotics, surgical drainage is indicated.

Patients with increased intracranial pressure (assessed by signs and neuroimaging findings) may benefit from a short course of high-dose corticosteroids (dexamethasone 10 mg IV once, then 4 mg IV every 6 hours for 3 or 4 days).

Antiseizure drugs are frequently used to prevent seizures.

Rate of recovery depends on how successful the abscesses are eradicated and the patient's immune status.

If immunocompromised patients (eg, patients with uncontrolled HIV infection) have an abscess due to Toxoplasma gondii or a fungus, they may have to take antibiotics for the rest of their life.