Brain abscess is a free or encapsulated collection of pus that usually occurs in the temporal lobe, cerebellum, or frontal lobes. It can vary in size and may present singly or multilocularly. Brain abscess has a relatively low occurrence. Although it can occur at any age, it’s most common in people ages 10 to 35 and is rare in older adults.
An untreated brain abscess is usually fatal; with treatment, the prognosis is only fair. About 30% of patients develop focal seizures. Multiple metastatic abscesses secondary to systemic or other infections have the poorest prognosis.
A brain abscess usually occurs secondary to some other infection, especially otitis media, sinusitis, dental abscess, and mastoiditis. Other causes include subdural empyema; bacterial endocarditis; human immunodeficiency virus infection; bacteremia; pulmonary or pleural infection; pelvic, abdominal, and skin infections; and cranial trauma, such as a penetrating head wound or compound skull fracture.
This condition also occurs in about 2% of children with congenital heart disease, possibly because the hypoxic brain is a good culture medium for bacteria. Common infecting organisms are pyogenic bacteria, such as Staphylococcus aureus and Streptococcus viridans. Penetrating head trauma or bacteremia usually leads to staphylococcal infection; pulmonary disease, to streptococcal infection. In up to 25% of patients, an original source isn’t discovered.
A brain abscess usually begins with localized inflammatory necrosis and edema, septic thrombosis of vessels, and suppurative encephalitis. This is followed by thick encapsulation of accumulated pus, and adjacent meningeal infiltration by neutrophils, lymphocytes, and plasma cells. Increasing pressure in the brain results in more damage.
Onset varies according to cause and location. Early signs and symptoms are characteristic of a bacterial infection and include headache, chills, fever, malaise, confusion, and drowsiness. Seizures, muscle weakness, and paresthesia can occur. The white blood cell count is elevated with a differential indicating infection. As the lesion enlarges, it produces symptoms similar to those of a brain tumor. At this time, symptoms correlate with a disturbance of function in the invaded lobe. Other features differ with the site of the abscess:
❑ temporal lobe abscess: auditory-receptive dysphasia, central facial weakness, hemiparesis
❑ cerebellar abscess: dizziness, coarse nystagmus, gaze weakness on the lesion side, tremor, ataxia
❑ frontal lobe abscess: expressive dysphasia, hemiparesis with unilateral motor seizure, drowsiness, inattention, mental function impairment, seizures.
A history of infection — especially of the middle ear, mastoid, nasal sinuses, heart, or lungs — or a history of congenital heart disease, along with a physical examination showing such characteristic indications as increased intracranial pressure (ICP), points to a brain abscess. An enhanced computed tomography (CT) scan and, occasionally, arteriography (which highlights the abscess by a halo) help locate the site.
Examination of cerebrospinal fluid can help confirm infection, but lumbar puncture is too risky because it can release the increased ICP and provoke cerebral herniation. A CT-guided stereotactic biopsy may be performed to drain and culture the abscess. Other tests include culture and sensitivity of drainage to identify the causative organism, skull X-rays, and a radioisotope scan.
Therapy consists of an antibiotic to combat the underlying infection and surgical aspiration or drainage of the abscess. However, surgery is delayed until the abscess becomes encapsulated (a CT scan helps determine this) and is contraindicated in patients with congenital heart disease or another debilitating cardiac condition. Administration of a penicillinase-resistant antibiotic, such as nafcillin or methicillin, for at least 2 weeks before surgery can reduce the risk of spreading infection.
Other treatments during the acute phase are palliative and supportive; they include mechanical ventilation and administration of I.V. fluids with a diuretic (urea, mannitol) and a glucocorticoid (dexamethasone) to combat increased ICP and cerebral edema. An anticonvulsant, such as phenytoin or phenobarbital, can help prevent seizures.
❑ The patient with an acute brain abscess requires intensive care monitoring.
❑ Frequently assess neurologic status, especially cognition and mentation, speech, and sensorimotor and cranial nerve function.
CLINICAL TIP: Early increases in ICP can be detected by using such diagnostic tools as the mini-mental status examination, Glasgow Coma Scale, and National Institutes of Health Stroke Scale. These highly sensitive tools facilitate recognition of early neurologic changes and may assist in retarding the increase of ICP. Once increased ICP results in abnormal pupils, depressed respirations, widened pulse pressure, and tachycardia or bradycardia, the cycle of increased ICP may be irreversible.
❑ Assess and record vital signs at least every hour.
❑ Monitor fluid intake and output carefully because fluid overload could contribute to cerebral edema.
❑ If surgery is necessary, explain the procedure to the patient and answer his questions.
❑ After surgery, continue frequent neurologic assessment. Monitor vital signs and intake and output.
❑ Watch for signs and symptoms of meningitis (including nuchal rigidity, headaches, chills, and sweats), an ever-present threat.
❑ Change the dressing often. Never allow bandages to remain damp. Reinforce the dressing, or change it as ordered. To promote drainage and prevent reaccumulation of the abscess, position the patient on the operative side. Measure drainage from Hemovac or other types of drains as instructed by the surgeon.
❑ If the patient remains stuporous or comatose for an extended period, give meticulous skin care to prevent pressure ulcers, and position him to preserve function and prevent contractures.
❑ If the patient requires isolation because of postoperative drainage, make sure he and his family understand why.
❑ Ambulate the patient as soon as possible to prevent immobility and encourage independence.
❑ To prevent brain abscess, stress the need for treatment of otitis media, mastoiditis, dental abscess, and other infections. Administer a prophylactic antibiotic, as needed, after a compound skull fracture or penetrating head wound.
Read excerpts from these other book chapters related to Abscess:
Copyright Details: Handbook of Diseases, Copyright © 2008 Williams & Wilkins.
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Title: Handbook of Diseases Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2003 ISBN: 1-58255-266-5 
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