Subdural empyema is a collection of pus that accumulates in the space between the dura mater and arachnoid mater. This is a life-threatening condition that should be diagnosed and treated urgently. In most cases, it emerges as a complication of paranasal sinusitis or otitis media.
Subdural empyema (SDE) is a life-threatening neurological condition that frequently has a rapid and aggressive course. This medical emergency is typically featured by the clinical triad of fever, sinusitis, and neurological deficits. Also, patients experience symptoms such as nausea, emesis, and headache , of which the latter is initially characterized as focal but then evolves to generalized. Moreover, the vast majority of patients exhibit meningeal signs such as nuchal rigidity and photophobia. Neurologic signs include hemiparesis, hemiplegia, gait abnormalities, dysphagia, and visual changes. Patients also develop seizures and mental status changes such as confusion, drowsiness, stupor, or even coma.
Remarkable findings on the neurologic exam include aphasia, contralateral motor deficits, gait ataxia, and possibly palsies of the oculomotor, trigeminal, and abducens cranial nerves. Ophthalmologic exam shows papilledema, which is reflective of elevated intracranial pressure. An altered mental status is also apparent.
It should be noted that the clinical presentation of subdural empyema closely resembles that of other forms of intracranial infections. Hence, the differential diagnoses are meningitis, viral encephalitis, brain abscess, and cerebritis  .
When evaluating an individual with a clinical picture suggestive of subdural empyema, the medical team should obtain a detailed history including any recent infections such as sinusitis, otitis media, respiratory infection, meningitis, or sinus/cranial surgery. Very importantly, a thorough physical exam must be performed. Finally, diagnostic studies are a crucial component of the workup.
Critical studies include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) , a complete metabolic panel (CMP), and blood cultures.
Magnetic Resonance Imaging (MRI) with gadolinium enhancement is the preferred diagnostic study  . The hallmark feature of subdural empyema on MRI is the appearance of a fluid collection surrounded by an enhanced rim. Moreover, MRI with diffusion-weighted imaging will provide information about intra-axial lesions . Overall, MRI is more sensitive than computed tomography (CT) for sinogenic intracranial infections .
Historically, CT testing has been considered important for the diagnosis of subdural empyema  and is the test of choice in patients with contraindications to MRI, those who are critically ill, or if MRI is not available or possible . CT scan displays subdural empyema as a hypodense region. While nonenhanced CT is insensitive, contrast-enhanced CT improves the diagnostic accuracy.
Other imaging techniques that may be used include cranial ultrasound, radionuclide brain scan, and angiography.