Intracranial epidural abscess

Epidural empyema refers to a collection within the epidural space either within the cranium or the spinal cord.

Epidemiology

Epidural empyemas are rare overall but together with subdural empyema account for around 20-33% of all intracranial infections. They can present in any age group and have no real gender predilection. 

Clinical presentation

Epidural empyema presents similar to other intracranial infections with:

• fever
• headache
• nuchal rigidity
• focal neurologic deficits or seizures may also occur in cases of large space-occupying empyemas

In patients with empyema of the spinal cord paraparesis or quadriplegia may be present.

Patients may also have active sinusitis, with epidural empyema being a potential complication of the condition.

Pathology

The most commonly isolated pathogens are Streptococci pneumoniae, Haemophilus influenzae, Staphylococcus aureus and Staphylococcus epidermidis.

In more than two-thirds of cases epidural empyema is a complication of sinusitis. Seeding can be via direct invasion through the sinus walls or haematogenous seeding through retrograde valveless bridging veins.

Another significant cause is mastoiditis which accounts as the cause in approximately 20% of cases. Epidural empyemas can also occur as a result of trauma, epidural injections or anaesthesia, open head or spinal trauma, neurosurgery or meningitis.

Radiographic features

CT

CT is less sensitive for the detection of epidural empyema compared to MRI. Features on CT include:

• extra-axial location
• isodense or hypodense to surrounding brain
• biconvex shape
• usually do not cross suture lines
• may cross the midline
• strong peripheral enhancement with contrast

MRI

Characteristics on MRI include:

• T1: hyperintense

• T1 C+ (Gd): strong peripheral contrast enhancement
• T2/FLAIR: isointense or hyperintense
• PD: isointense or hyperintense
• DWI: area of restricted diffusion

Treatment and prognosis

Prompt recognition and surgical evacuation of the collection is essential to the management of epidural empyema. It may be fatal in up to 15% of cases.

See also

• subdural empyema
• cerebral abscess
• spinal epidural abscess