Subdural empyema overview

# Overview
Subdural empyema is a life-threatening infection, consisting of a localized collection of purulent material, usually unilateral, between the dura mater and the arachnoid mater. Subdural empyema may be classified according to location of the infection into 2 groups: intracranial and spinal, with intracranial being the more common of the two groups, accounting for 95% of subdural empyema patients. Subdural empyema accounts for approximately 15-25% of focal central nervous system infections. In 2014, the incidence of subdural empyema was estimated to be less than 1 case case per 100,000 individuals, with a male predominance. 
The most common pathogens in intracranial subdural empyema are anaerobic and microaerophilic Streptococci, compared to spinal subdural epmyema, which can be caused by either Streptococci or Staphylococcus aureus. If left untreated, subdural empyema frequently evolves into severe fever, headache, nausea, vomiting, seizures, coma, and subsequent mortality. Complications to subdural empyema include status epilepticus, neurological deficits, and thrombosis. Prognosis is generally good with antimicrobial therapy. Physical examination of patients with subdural empyema is usually remarkable for fever, facial pain, and altered mental status. MRI is the primary imaging study of epidural abscess, with CT scan as a secondary alternative. Treatment of subdural empyema requires a combined medical and surgical approach. In order to evacuate the pus, burr hole placement or craniotomy may be used to treat the subdural empyema. The preferred surgical mainstay of treatment for subdural empyema is craniotomy.

# Historical Perspective
In 1869, subdural empyema was first operated on by Francois Gigot de la Peyronie. The first detailed description of the disease was by Cyril Brian Courville in 1939.

# Classification
Subdural empyema may be classified according to location of the infection into 2 groups: intracranial and spinal.

# Pathophysiology
Subdural empyema is a localized collection of pus between the dura mater and arachnoid mater, occurring in either the intracranial space or the spinal canal. Subdural empyema generally follows the same progression for both intracranial and spinal subtypes, spreading via blood or from nearby infection. Bacterial infections of the skull 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.

# Causes
Common causes of subdural empyema include Streptococci, Staphylococci, and other Gram-negative bacilli. In children, the majority of cases of subdural empyema occur due to meningitis, while in adults the most common causes are sinusitis, otitis media, mastoiditis, and trauma.

# Differentiating Subdural Empyema from Other Diseases
Subdural empyema must be differentiated from other diseases that cause fever, headache, focal neurological signs, seizures, and altered mental status, such as subdural hematoma, brain abscess, and bacterial meningitis. These conditions may be distinguished from subdural empyema by their clinical findings, brain imaging findings, and laboratory studies.

# Epidemiology and Demographics
Subdural empyema accounts for approximately 15-25% of focal central nervous system infections. In 2014, the incidence of subdural empyema was estimated to be less than 1 case per 100,000 individuals. Prior to antibiotics, the case fatality rate of subdural empyema was estimated to be near 100%. However, with antibiotics, the current rate is estimated between 10-20%. The disease usually occurs in children and young adults (70% cases occurring in the second and third decades of life), being more frequent in men than women, possibly due to sex-related differences in sinus anatomy.

# Risk Factors
Common risk factors in the development of subdural empyema are meningitis, sinusitis, otitis, mastoiditis, immunodeficiency, head trauma, and lumbar puncture.

# Natural History, Complications, and Prognosis
If left untreated, subdural empyema frequently evolves into severe fever, headache, nausea, vomiting, seizures, coma, and subsequent mortality. Complications to subdural empyema include status epilepticus, neurological deficits, and thrombosis. Prognosis is generally good with antimicrobial therapy.

# Diagnosis

## History and Symptoms
If possible, a detailed and thorough history from the patient is necessary. Specific areas of focus when obtaining a history from the patient include prior neurosurgery, sinusitis, or mastoiditis. Common symptoms of subdural empyema include headache, altered mental status, vomiting, and seizures.

## Physical Examination
Physical examination of patients with subdural empyema is usually remarkable for fever, facial pain, and altered mental status.

## Laboratory Findings
Laboratory findings associated with subdural empyema are generally unspecific. Often, elevated inflammatory markers are present, including:
- Leukocytes
- Erythrocyte sedimentation rate
- C-reactive protein

## Lumbar Puncture
Lumbar puncture is not diagnostic of subdural empyema. Lumbar puncture is an invasive procedure which is contraindicated in case of suspicion of subdural empyema and increased intracranial pressure, due to risk of brain herniation, and mortality.

## X ray
Generally, x ray is not helpful in the diagnosis of subdural empyema.

## CT
Head CT scan may be helpful in the diagnosis of subdural empyema. CT scan is secondary to MRI for subdural empyema imaging. Findings on CT scan suggestive of subdural empyema include a crescentic shape, although collection pockets may appear bi-convex. A surrounding membrane that enhances intensely and uniformly following contrast administration is typically identified.

## MRI
MRI in the optimal imaging study in the diagnosis of subdural empyema. Findings on MRI suggestive of subdural empyema are similar to those on CT scan, and include a crescent or bi-convex shaped collection. A surrounding membrane that enhances intensely and uniformly following gadolinium enhancement is typically identified and may also demonstrate restricted diffusion.

# Treatment

## Medical Therapy
Subdural empyema is a medical emergency and requires prompt treatment. Treatment of subdural empyema requires a combined medical and surgical approach. Empiric antimicrobial therapy depends on the location of the infection (intracranial vs. spinal) and whether it was community-acquired or hospital-acquired. The clinical symptoms may be mild and unspecific initially.

## Surgery
Subdural empyema is a neurosurgical condition, which requires emergency surgical drainage and subsequent medical therapy. In order to evacuate the pus, burr hole placement or craniotomy may be used to treat the subdural empyema. The preferred surgical mainstay of treatment for subdural empyema is craniotomy. A wide craniotomy allows a wide exposure of the area, adequate exploration, and better evacuation of the infected material and decompression of the underlying cerebral hemisphere, thereby improving the outcome.

## Prevention
Effective measures for the primary prevention of subdural empyema include rapid treatment of inflammatory diseases of the head and prevention of trauma. Secondary prevention strategies following subdural empyema include treatment and management of existing infection.