Page 930 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 71: Bacterial Infections of the Central Nervous System 661

3 months is also suggested to monitor for abscess reexpansion or failure streptococci (25%-45% of cases), staphylococci (10%-15%), aerobic
to resolve. gram-negative bacilli (3%-10%), and anaerobes (33%-100%, when care-
ful culturing is performed); these organisms constitute the microbial
Surgical Therapy: Most patients require surgical management for opti- flora that are frequently isolated from patients with chronic sinusitis and
mal treatment of brain abscess. The two procedures judged equivalent cranial abscesses.
by outcome are aspiration of the abscess after burr hole placement and Spinal subdural empyema is a rare condition occurring secondary to
complete excision after craniotomy. 51,58,59 The choice of procedure must metastatic infection from a distant site. Staphylococcus aureus is the
64
be individualized for each patient. Aspiration may be performed using most frequent isolate, whereas streptococci are found less frequently.
stereotaxic CT guidance, which affords the surgeon rapid, accurate, and The term epidural abscess refers to a localized infection between the
safe access to virtually any intracranial point. Aspiration can also be dura mater and the overlying skull or vertebral column. Cranial epidural
64
used for swift relief of increased intracranial pressure. Incomplete drain- abscess can cross the cranial dura along emissary veins, so subdural
age of multiloculated lesions is a major disadvantage of aspiration; these empyema often is also present. Therefore, the etiology, pathogenesis,
lesions frequently require excision. Other risks of aspiration are that it and bacteriology of intracranial epidural abscess are usually identical
may allow the abscess to rupture into the ventricle, and that pus may to those described for subdural empyema (see above), with the initial
leak into the subarachnoid space, resulting in ventriculitis or meningitis. focus of infection in the middle ear, paranasal sinuses, or mastoid cells.
Complete excision after craniotomy is most often employed in In contrast, spinal epidural abscess usually follows hematogenous
patients in a stable neurologic condition. Surgery is also indicated for dissemination from foci elsewhere in the body to the epidural space or,
abscesses exhibiting gas on radiologic evaluation and for posterior fossa by extension, from vertebral osteomyelitis. 64-68 Hematogenous spread
abscesses. In patients with worsening neurologic deficits, including occurs in 25% to 50% of cases, secondary to infections of the skin
deteriorating consciousness or signs of increased intracranial pressure, (furuncles, cellulitis, or infected acne), urinary tract infections, peri-
surgery should be performed emergently. Excision is contraindicated in odontal abscesses, pharyngitis, pneumonia, or mastoiditis. Mild blunt
the early stages, before a capsule is formed. All brain abscesses larger spinal trauma (15%-35% of cases) may provide a devitalized site sus-
than 2.5 cm in diameter should be aspirated or excised for optimal ceptible to transient bacteremia. Infection of the epidural space has also
management. 52,60
been reported after penetrating injuries, extension of decubitus ulcers
Adjunctive Therapy: Intracranial pressure monitoring has become or paraspinal abscesses, back surgery, lumbar puncture, and epidural
important in the intensive care management of brain abscess patients anesthesia. Bacteremia may be an important predisposing factor because
who have cerebral edema (see Chap. 86). The use of these monitoring the incidence of spinal epidural abscess is increased in patients who
devices has diminished the likelihood of transtentorial herniation, brain use injection drugs or have intravenous catheters. The infecting micro-
stem compression, and further injury from cerebral ischemia. organism in the vast majority of cases is S aureus (50%-90% in vari-
Corticosteroids have been used as one method to manage increased ous series). Other isolates include aerobic and anaerobic streptococci
intracranial pressure, although their use remains controversial. These (8%-17% of cases) and gram-negative aerobic bacilli (10%-17%), espe-
52
agents may retard the encapsulation process, reduce antibiotic entry into cially E coli and P aeruginosa.
the CNS, increase necrosis, and alter the appearance of ring enhance- ■
ment on CT as inflammation subsides, thereby obscuring information CLINICAL PRESENTATION
from sequential studies. Steroids (at a dexamethasone dose for adults of Persons with subdural empyema can present in a rapidly progressive,
4 to 6 mg every 6 hours) are most useful in the patient with deteriorat- life-threatening clinical condition. 61-64 Symptoms and signs relate to the
ing neurologic status and increased intracranial pressure, for whom presence of increased intracranial pressure, meningeal irritation, or focal
steroids may prove lifesaving. When used to treat cerebral edema, ste- cortical inflammation. In addition, 60% to 90% of patients have evidence
roids should be used for the shortest time possible and withdrawn when of the antecedent infection (eg, sinusitis or otitis). Headache, initially
the mass effect no longer poses a significant danger to the patient. The localized to the infected sinus or ear is a prominent complaint and can
management of increased intracranial pressure is discussed in Chap. 86. become generalized as the infection progresses. Vomiting is common
as intracranial pressure increases. Early in the infection, about 50% of
patients have altered mental status, which can progress to obtundation
SUBDURAL EMPYEMA AND EPIDURAL ABSCESS if the patient is not treated. Fever with a temperature above 39°C is
■ EPIDEMIOLOGY AND ETIOLOGY present in most cases. Focal neurologic signs appear in 24 to 48 hours
and progress rapidly, with eventual involvement of the entire cerebral
The term subdural empyema refers to a collection of pus in the space hemisphere. Hemiparesis and hemiplegia are the most common focal
between the dura and arachnoid. This process accounts for about 15% signs, although ocular palsies, dysphasia, homonymous hemianopsia,
to 20% of all localized intracranial infections. 61-64 The disease was essen- dilated pupils, and cerebellar signs have been observed. Seizures (focal
tially lethal before the advent of antimicrobial therapy, with current or generalized) are observed in 25% to 80% of cases. Signs of menin-
methods of diagnosis and treatment, mortality rates are 10% to 20%. geal irritation (eg, meningismus) are found in approximately 80% of
The most common predisposing conditions are otorhinologic infec- patients, although fewer have Kernig or Brudzinski sign. If the patient
tions, especially infection of the paranasal sinuses, which are affected in remains untreated, neurologic deterioration occurs rapidly, with signs
40% to 80% of cases. The pathogenesis involves spread of infection to of increased intracranial pressure and cerebral herniation. Papilledema
the subdural space through valveless emissary veins in association with develops in fewer than 50% of patients. This fulminant picture may
thrombophlebitis or by extension of an osteomyelitis of the skull with not be seen in patients with subdural empyema after cranial surgery or
accompanying epidural abscess. The mastoid cells and middle ear are the trauma, in patients who have received prior antimicrobial therapy, in
source in 10% to 20% of patients, especially in geographic areas where patients with infected subdural hematomas, or in patients with infec-
many cases of otitis media are not treated promptly with antibiotics. tions metastatic to the subdural space.
Other predisposing conditions include skull trauma, neurosurgical Spinal subdural empyema usually manifests as radicular pain and
procedures, and infection of a preexisting subdural hematoma. The symptoms of spinal cord compression, which may occur at multiple
infection is metastatic in a minority of cases (∼5%), principally from levels. Clinically, this lesion is difficult to distinguish from a spinal
64
the pulmonary system. In infants, meningitis is an important predispos- epidural abscess (see the section Diagnosis below).
ing condition for the development of subdural empyema, which occurs The onset of symptoms in cranial epidural abscess may be insidi-
in about 2% of infants with bacterial meningitis. Different bacterial ous and overshadowed by the primary focus of infection (eg, sinusitis
64
species have been isolated from cranial subdural empyemas, including or otitis media). Headache is a usual complaint, but the patient may

section05_c61-73.indd 661 1/23/2015 12:48:38 PM