Intracranial Epidural Abscess

Epidemiology

Far less common than spinal epidural abscess
Intracranial epidural abscess is the third most common type of focal intracranial infection, after brain abscess and subdural empyema
Historically, most cases of intracranial epidural abscess were associated with spread from contiguous cranial infections (such as otitis, mastoiditis, and sinusitis), but currently, neurosurgery is the most common etiology

Contiguous Focus of Intracranial Infection: direct extension into the epidural space
- Mastoiditis (see Mastoiditis)
- Otitis (see Otitis)
- Osteomyelitis (see Osteomyelitis)
- Sinusitis (see Sinusitis)
Fetal Monitoring Probes: used obstetrically
Neurosurgery: surgical invasion of the epidural space
Trauma: direct inoculation into the epidural space

Anatomic Relationships: the intracranial dura forms the inner lining of the skull (and is firmly adherent to the skull bone): in normal anatomy, the epidural space is only a virutal space
- Epidural space can be “opened” by invasion by tumor cells, blood, inflammatory masses (granulation tissue), or pus
- Due to firm adherence of dura to the skull bone, invasion and creation of the epidural space is typically a gradual process (with dissection of the dura away from the bone), forming a rounded and well-localized collection
- Spread from the intracranial space caudally into spinal epidural space is rare, as the dura is tightly adherent around the foramen magnum

Culture
- Microaerophilic/Anaerobic Strep: associated with sinusitis and otitis cases
- Propionibacterium (anaerobe): associated with sinusitis and otitis cases
- Peptostreptococcus (anaerobe): associated with sinusitis and otitis cases
- Gram-Negative Rods: occasionally isolated
- Haemophilus species
- Staph Epi/Staph Aureus: associated with neurosurgical cases
- Fungi: occasionally isolated
Head CT: typically rounded (lenticular) collection
- May be surrounded by inflammatory reaction
- May be calcified
CT-Guided Aspiration: may be performed
Brain MRI: preferred imaging modality

Slowly-Expanding Intracranial Mass
- Focal neurologic signs
- Increased intracranial pressure
Fever/Headache: common
Nausea/Vomiting: common
Purulent Drainage from Nose/Ear: may occur in sinusitis-associated cases

Burr Hole/Craniotomy for Drainage: usually required
- If dura is breached, may require dural repair with a fascial graft
Management of Sinusitis: sinus drainage may be adequate without surgery in some childhood sinusitis-associated cases without intracranial mass effect
Antibiotics: directed against the isolated organism