Subdural Empyema

Abstract

A subdural empyema is a collection of pus in the space between the dura and the arachnoid. Paranasal sinusitis is the most common predisposing condition associated with a subdural empyema. A subdural empyema may also complicate a neurosurgical procedure when there is direct infection of the subdural space during either drainage of a subdural hematoma or craniotomy. Once infection is established in the subdural space, evolution of an empyema tends to be remarkably rapid. The exudate can spread extensively throughout the subdural space. The majority of subdural empyemas develop over the convexity of the cerebral hemispheres. Aerobic, microaerophilic, and anaerobic streptococci are the predominant organisms isolated in empyemas, complicating sinusitis, otitis, and mastoiditis. Staphylococcus aureus and coagulase-negative staphylococci are found in subdural empyemas that complicate neurosurgical procedures. The initial signs and symptoms of subdural empyema are headache, which is initially localized to the side of the subdural infection but then becomes severe and generalized; fever; and nuchal rigidity. This is followed by a change in the level of consciousness progressing from confusion and somnolence to stupor and coma. Focal neurological deficits are present in 80–90% of patients. A subdural empyema is best demonstrated by magnetic resonance imaging with a gadolinium-enhanced, T1-weighted image, which demarcates the empyema from the brain, and a T2-weighted image, which demonstrates a crescent-shaped lesion of higher signal intensity than that of cerebrospinal fluid. The etiological organism of a subdural empyema is identified by Gram's stain and culture of pus obtained either via burr holes or via craniotomy. Neurosurgical evacuation of the empyema, through either burr hole drainage or craniotomy, is the definitive step in the management of this infection and should be done in an emergent manner. Empirical antibiotic therapy should be based on the likely etiological organism based on the primary source of infection.