(See also Introduction to Brain Infections Introduction to Brain Infections Brain infections can be caused by viruses, bacteria, fungi, or, occasionally, protozoa or parasites. Encephalitis is most commonly due to viruses, such as herpes simplex, herpes zoster, cytomegalovirus... read more .)
An abscess forms when an area of cerebral inflammation becomes necrotic and encapsulated by glial cells and fibroblasts. Edema around the abscess may increase intracranial pressure, as may the abscess itself.
Etiology of Brain Abscess
A brain abscess can result from
Direct extension of cranial infections (eg, osteomyelitis Osteomyelitis Osteomyelitis is inflammation and destruction of bone caused by bacteria, mycobacteria, or fungi. Common symptoms are localized bone pain and tenderness with constitutional symptoms (in acute... read more , mastoiditis Mastoiditis Mastoiditis is a bacterial infection of the mastoid air cells, which typically occurs after acute otitis media. Symptoms include redness, tenderness, swelling, and fluctuation over the mastoid... read more , sinusitis Sinusitis Sinusitis is inflammation of the paranasal sinuses due to viral, bacterial, or fungal infections or allergic reactions. Symptoms include nasal obstruction and congestion, purulent rhinorrhea... read more , subdural empyema Intracranial Epidural Abscess and Subdural Empyema Intracranial epidural abscess is a collection of pus between the dura mater and skull. Subdural empyema is a collection of pus between the dura mater and the underlying arachnoid mater. Symptoms... read more )
Penetrating head wounds (including neurosurgical procedures)
Hematogenous spread (eg, in bacterial endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more , congenital heart disease with right-to-left shunt, or IV drug abuse)
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 and Signs of Brain Abscess
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.
Diagnosis of Brain Abscess
Contrast-enhanced MRI or, if unavailable, contrast-enhanced CT
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 ).
Treatment of Brain Abscess
Antibiotics (initially cefotaxime or ceftriaxone plus metronidazole for Bacteroides species or plus vancomycin for Staphylococcus aureus based on suspicion, then as guided by culture and susceptibility testing)
Usually CT-guided stereotactic aspiration or surgical drainage
Sometimes corticosteroids, antiseizure drugs, or both
All patients receive antibiotics for a minimum of 4 to 8 weeks. Initial empiric antibiotics include one of the following:
Cefotaxime 2 g IV every 4 hours
Ceftriaxone 2 g IV every 12 hours
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.
Brain abscess can result from direct extension (eg, of mastoiditis, osteomyelitis, sinusitis, or subdural empyema), penetrating wounds (including neurosurgery), or hematogenous spread.
Headache, nausea, vomiting, lethargy, seizures, personality changes, papilledema, and focal neurologic deficits develop over days to weeks; fever may be absent at presentation.
Do contrast-enhanced MRI or, if MRI is unavailable, contrast-enhanced CT.
Treat all brain abscesses with antibiotics (usually initially with ceftriaxone or cefotaxime plus metronidazole if clinicians suspect Bacteroides species or plus vancomycin if they suspect S. aureus), typically followed by CT-guided stereotactic aspiration or surgical drainage.
If abscesses are < 2 cm in diameter, they may be treated with antibiotics alone but must then be monitored closely with MRI or CT; if abscesses enlarge after being treated with antibiotics, surgical drainage is indicated.
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