Subdural empyema overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Subdural empyema, also referred to as subdural abscess, pachymeningitis interna and circumscript meningitis, is a life-threatening infection, first reported in literature approximately 100 years ago. It consists of a localised collection of purulent material, usually unilateral, between the dura mater and the arachnoid mater. It accounts for about 15-22% of the reported focal intracranial infections. The empyema may develop intracranially (about 95%) or in the spinal canal (about 5%), and in both cases, it constitutes a medical and neurosurgical emergency. The intracranial type tends to behave like an expanding mass, causing clinical symptoms, such as fever, lethargy, headache and neurological deficits. These, result from the extrinsic compression of the brain, caused not only from the inflammatory mass, but also from the inflammation of the brain and meninges. Because the subdural space has no septations, except in areas where arachnoid granulations attach to the dura mater, the subdural empyema tends to spread quickly, until it finds those boundaries. In children, subdural empyema happens most often as a complication of meningitis, while in adults it usually occurs as a complication of sinusitis, otitis media, mastoiditis, trauma or as a complication of neurological procedures. The most common pathogens in the intracranial type are anaerobic and microaerophilic streptococci however, others like Escherichia coli and Bacteroides may be present simultaneously. Spinal subdural empyemas, on the other hand, are almost always caused by streptococci or by staphylococcus aureus. The classic clinical syndrome includes acute fever, that rapidly progresses into neurological deterioration, which if left untreated will eventually lead to a coma and death. The diagnostic procedure of choice is the MRI with gadolinium enhancement. Since the clinical symptoms might be mild and unspecific initially, the rapid diagnosis and treatment are crucial. The sooner the proper treatment is initiated, the better the recovery will be. The treatment, for almost all causes, requires prompt surgical drainage and antibiotic therapy. With treatment, resolution of the empyema occurs from the dural side, and, if it is complete, a thickened dura may be the only residual finding.

Pathophysiology

Bacterial or occasionally fungal infection of the skull bones or air sinuses can spread to the subdural space, producing a subdural empyema. The underlying arachnoid and subarachnoid spaces are usually unaffected, but a large subdural empyema may produce a mass effect. Further, a thrombophlebitis may develop in the bridging veins that cross the subdural space, resulting in venous occlusion and infarction of the brain. If diagnosis and treatment are prompt, complete recovery is usual.

Epidemiology and Demographics

Subdural empyema, also referred to as subdural abscess, pachymeningitis interna and circumscript meningitis, is a life-threatening infection. It consists of a localised collection of purulent material, usually unilateral, between the dura mater and the arachnoid mater and accounts for about 15-22% of the reported focal intracranial infections The empyema may develop intracranially (about 95%) or in the spinal canal (about 5%), and in both cases, it constitutes a medical and neurosurgical emergency. Bacterial or occasionally fungal infection of the skull bones or air sinuses can spread to the subdural space producing a subdural empyema.

Causes

Subdural empyema, also referred to as subdural abscess, pachymeningitis interna and circumscript meningitis, is a life-threatening infection. It consists of a localised collection of purulent material, usually unilateral, between the dura mater and the arachnoid mater and accounts for about 15-22% of the reported focal intracranial infections The empyema may develop intracranially (about 95%) or in the spinal canal (about 5%), and in both cases, it constitutes a medical and neurosurgical emergency. Depending on the site of origin of the infection, as well as location of the empyema in the subdural space, there will be different causative agents. The rate of success of bacterial cultures from the surgically removed pus is 54-81%. Common agents of subdural empyema include: anaerobes, aerobic streptococci, staphylococci, Haemophilus influenzae, Streptococcus pneumoniae and other gram-negative bacilli. In children, subdural empyema most often happens as a complication of meningitis while in adults it usually occurs as a complication of sinusitis, otitis media, mastoiditis trauma or as a complication of neurological procedures.

Diagnosis

Symptoms

Symptoms include those referable to the source of the infection.

In the case of infants, common symptoms will include:

• altered mental status
• fever
• neck stiffness
• headache, nausea/vomiting, ocular palsies
• seizures

In the case of most adult patients, common symptoms are

• fever
• sinusitis
• headache
• neck stiffness

If untreated, my develop:

• focal neurologic signs
• lethargy
• coma

Laboratory Findings

Patients with subdural empyema usually have:

• elevated white blood cell count
• elevated erythrocyte sedimentation rate
• elevated C-reactive protein

Children with hyperglycaemia or diabetes have an increased risk of developing sinogenic intracranial empyema.

The CSF profile is similar to that seen in brain abscesses, because both are parameningeal infectious processes:

• increased white blood cell count
• increased protein level
• decreased glucose levels
• occasionally CSF results may be normal and sterile

Treatment

Medical Therapy

The clinical symptoms might be mild and unspecific initially. The rapid diagnosis and treatment are crucial, the sooner the proper treatment is initiated, the better the recovery will be. The treatment, for almost all causes, requires prompt surgical drainage (via burr hole procedure or craniotomy) and antibiotic therapy, which should be broad-spectrum initially, and adjusted to the organism , once results from the drained infected material are know. With treatment, including surgical drainage, resolution of the empyema occurs from the dural side, and, if it is complete, a thickened dura may be the only residual finding.