epidural empyemas

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Intracranial epidural abscess, less commonly called epidural empyema, refers to a pyogenic collection within the epidural space of the head. Spinal epidural abscess is discussed separately.

Similarly to subdural empyemas, sinusitis is the most common cause of intracranial epidural abscesses.

On imaging, it tends to present as an epidural collection of biconvex shape, usually not crossing the suture lines, and with marked meningeal enhancement. On MRI, typically demonstrates restricted diffusion.

Epidemiology

Epidural abscesses 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 abscess 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

Patients may also have active sinusitis, with epidural abscess 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, an epidural abscess 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 abscesses can also occur as a result of trauma, epidural injections or anesthesia, open head or spinal trauma, neurosurgery or meningitis.

Radiographic features

CT

CT is less sensitive for the detection of epidural abscess 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 abscess. It may be fatal in up to 15% of cases.