Cranial extradural abscess

General

Collection in the extradural space, which is only a potential space, is designated an abscess

Extradural abscesses are often located in the frontal region and are limited by sutures

Definition

Cranial extradural abscess is a suppurative infection that arises between the inner table of the skull and the dura as a result of contiguous spread from adjacent structures.

Numbers

Incidence unknown

3rd most common localized intracranial infection, following brain abscesses and subdural empyemas (77) ICNS

1.8% of all intracranial infections (78) ICNS

Affects all ages (77–79) ICNS

Aetiology (Calfee and Wispelwey, 1999)

Contiguous infections

Mainly
Sinusitis and otitis/mastoiditis -main (81–84) ICNS
Skull osteomyelitis
Dental infection: rare

Direct spread

Infection after neurosurgical procedures
Infection after head trauma with skull fracture and open wound.

With postoperative and posttraumatic extraaxial abscesses often present months to years following surgery or head trauma, respectively

Other

Congenital osseous defects of the anterior cranial fossa that facilitate communication between the epidural space and the paranasal sinuses

Pathogenesis

Pathology

Abscess expands as the pressure generated by the growing inflammatory mass dissects the dura away from the skull → epidural abscess is a slowly growing mass → insidious clinical presentation.

Intracranial extradural abscesses rarely dissect beyond the base of the skull because there the dura is even more tightly fixed.

Microbiology

Similar to subdural empyema

S. aureus
Streptococcus
Gram-negative bacilli
Tuberculosis

Streptococci and staphylococci (including Staphylococcus epidermidis and MRSA) are the leading pathogens in postoperative epidural abscess (7884)- ICNS.

Complication (Pradilla et al., 2009)

Skull osteomyelitis

Edema and cellulitis of the face and scalp

Expanding abscess

This may result from the development of thrombosis of the valveless emissary veins that run between the skull and meninges

Dural venous sinus thrombosis

It may result from direct penetration through the necrotic dura.

Purulent leptomeningitis
Subdural empyema
Brain abscess

If the dura mater is breached or with spread via dural venous anastomoses, empyema can progress into the subdural space or cause thrombophlebitis and cerebritis

Epidural abscess and subdural empyema. Enhanced computed tomographic scan demonstrates a large convexity, low-density subdural collection and a small anterior rim-enhancing epidural lesion (arrow).

Clinical features

Insidious onset and fever or headache may be the only clinical presentation.

Symptoms this may take weeks/months to develop (78).

May have subtle clinical signs and neurological deficits only occur when there is sufficient mass effect caused by the collection.

In 82 spontanoeus cases (78) ICNS

Fever (57%),
Frontal subgaleal abscess (Pott puffy tumor, 46%),
Periorbital edema (40%),
Headache (37%),
Meningismus (35%),
Seizures (11%)

Meningitis/brain involvement

In Postop cases (80) ICNS

Wound infection (95.7%),
Encephalopathy (44.7%)
Fever (34.8%)
Headache (17.4%)

LP

Not useful (78) ICNS

CSF findings are nonspecific
Cultures are usually negative
Considerable risk of neurologic deterioration following lumbar puncture because of transtentorial or foraminal herniation

A lumbar puncture should, therefore, not be performed in patients with suspected or proven epidural abscess.

Evaluation

Lentiform-shaped enhancing lesion and a thickened dural surface that reliably distinguishes epidural abscess from sterile epidural collection.

Thick medial rim enhancement, which represents inflamed displaced dura

Post op/post trauma abscess

Patients with postoperative and posttraumatic abscesses have underlying structural brain lesions that may lead to the persistence or the reaccumulation of these collections.
Postoperative abscesses occupy the cavity created by the craniotomy defect
Posttraumatic abscesses are often an iatrogenic complication of evacuation of a preexisting subdural or epidural hematoma
Difficult to differentiate posttraumatic/operative vs noninfected sterile effusions or chronic extraaxial hematomas.

A change in density of these collections on serial CT scans, associated with subtle mass effect on adjacent brain, may be the first indication of an intracranial infection.

CT+C

CT may also show bony destruction and fragmentation in patients with underlying skull osteomyelitis or mastoiditis.
The degree of rim enhancement is usually thicker and more irregular in an epidural abscess than in subdural empyema
An intracranial epidural abscess rarely demonstrates parenchymal abnormalities on CT

It is important to appreciate that an intracranial epidural abscess often coexists with a subdural empyema, so presence of the former should prompt a careful search for the latter.

T1: mildly hyperintense to CSF
T2: markedly hyperintense to CSF

Sterile effusions are isointense to CSF (92,94).

Posttraumatic abscesses

T1/T2 hypointense (94).

Advantage of MRI

In otorhinologically induced abscesses, MRI can accurately identify and delineate the collections (including small loculations) early in the stage of disease, when the findings on CT can be subtle (92).

This ability of MRI is attributable to the inherent high degree of contrast between the purulent collections and the subjacent calvaria, brain, and CSF, combined with the absence of streak artifacts from bone

DWI helps differentiate:

Subdural vs Extradual (Tsuchiya et al., 2003).

Subdural empyema high signal intensity
Extra dural abscess low or mixed signal intensity

In postoperative and posttraumatic abscesses:

Collections from sterile effusions VS chronic extraaxial hematomas
MRI shows a signal-intensity differences, a distinction that is usually subtle or undetectable on CT.

Treatment

Formal craniotomy or drainage through burr holes or an extended craniectomy), surgical therapy of underlying infections, and medical therapy.

Antibiotics

Empirical

Community-acquired epidural abscesses:

3rd-generation cephalosporin (e.g., ceftriaxone) + metronidazole

Postoperative or posttraumatic epidural cranial abscesses

Vancomycin + meropenem.

After culture results, the therapy should be modified according to the antibiogram.

Surgery

Aims

Drainage of the collection to prevent further accumulation and neurologic damage
Obtaining material for culture.

Options

Burr holes
Craniotomy
Craniectomy

Indicated

Osteomyelitis (Tsai et al., 2003).

Evidence Nathoo et al. (78) adequate drainage

Burr holes (21 of 70 patients treated surgically)
Limited craniectomies (39 of 70 patients)

Because the extradural pus collections were usually liquid and never loculated.

Prognosis

Postoperative infections (80)

18% 5-year case-fatality rate was attributed primarily to comorbidities rather than the intracranial infectious process

Nathoo (78) 82 patients,

78 patients recovered completely,
3 had a moderate disability, and
1 died (mortality rate, 1.2%)

Delays in diagnosis may result in irreversible neurologic deficits,

Prognosis is inversely related to the degree of encephalopathy at initial presentation.

Difference between Subdural empyema and Extradural abscess

Extradural abscess they have a sharp demarcation, slower progression rate, and an indolent course owing to the tight adherence of the dura mater to the skull.