Epidural abscess overview

# Overview
An epidural abscess is an infection that forms in the epidural space. Specifically, intracranial epidural abscess is limited on the inner side by the cranial dura mater and on the outer side by the cranial bone. Spinal epidural abscess is limited on the inner side by the spinal dura mater and on the outer side, by the spinal canal. Spinal epidural abscess is the more common type of epidural abscess. Staphylococcus aureus is responsible for approximately 2/3 of the reported cases. Prevalence is greatest between the fifth and seventh decades of life, with a male predominance. If left untreated, intracranial epidural abscess may cause headache, fever, and seizures. If left untreated, spinal epidural abscess may cause back pain, nerve root pain, and paralysis. Complications of epidural abscess include neurological deficits, meningitis, and sepsis. Generally, epidural abscess is a medical emergency and requires prompt treatment. If treated timely, the prognosis for epidural abscess is generally good. Physical examination of patients with epidural abscess is usually remarkable for fever, back pain, and generally well appearance, often contributing to misdiagnosis. MRI is the primary imaging study of epidural abscess, with CT scan as a secondary alternative. A combination of surgical drainage and prolonged systemic antibiotics (6-12 weeks, IV followed by PO) is the mainstay of therapy for either intracranial or spinal epidural abscess. Due to the importance of preoperative neurologic status, along with the unpredictable progression of neurologic impairment, for the neurological outcome of the patient, surgical therapy varies depending on the location of the abscess.

# Historical Perspective
In general, abscesses were first described by Hippocrates between 400-370 B.C. Despite scientific advances, both epidural abscesses remain a serious health condition, with significant risks for patients. However, diagnosis, management and outcome have been considerably improved due to more accurate imaging studies, better antibiotics, and improved surgical techniques.

# Classification
Epidural abscess may be classified according to the location of the infection into 2 groups: intracranial and spinal. Additionally, spinal epidural abscess can be further classified based on the duration of symptoms into either acute or chronic.

# Pathophysiology
Epidural abscess pathophysiology differs based on the location of the infection and responsible organism. The majority of intracranial epidural abscess cases occur as a complication of cranial surgical procedures and sinusitis. The majority of spinal epidural abscess cases occur as a result of spinal instrumentation, vascular access, and IV drug use.

# Causes
Common causes of intracranial epidural abscess include paranasal sinusitis, osteomyelitis of the skull, and extension of infection from concurrent otitis or mastoiditis. Common causes of spinal epidural abscess include spinal instrumentation, vascular access, and IV drug use. Irrespective of cause, epidural abscess is a life-threatening, but treatable, condition.

# Differentiating Epidural Abscess from Other Diseases
Intracranial epidural abscess must be differentiated from epidural hematoma, subdural empyema, brain abscess, tuberculous meningitis, and other intracranial mass lesions. Spinal epidural abscess must be differentiated from other conditions that cause back pain, weakness, and spinal tenderness, such as arthritis, osteoarthritis, intervertebral disc disease, vertebral osteomyelitis, primary or metastatic tumors, and musculoskeletal pain.

# Epidemiology and Demographics
In general, epidural abscess is rare. Intracranial epidural abscess is the more rare type of epidural abscess and the 3rd most common focal intracranial infection. Spinal epidural abscess is more common than intracranial epidural abscess, however it is still rare in the general population, accounting for 2.5 to 3 cases per 10,000 hospital admissions per year. Estimates of the incidence following central nerve block vary from 1 per 1,000 hospital admissions to 1 per 100,000 hospital admissions. Prevalence of epidural abscess is greatest between the fifth and seventh decades of life.

# Risk Factors
Common risk factors in the development of intracranial epidural abscess include trauma, neurosurgical procedures, and infections such as sinusitis, otitis, and mastoiditis. Common risk factors for the development of spinal epidural abscess include diabetes mellitus, trauma, and bacteremia.

# Natural History, Complications, and Prognosis
If left untreated, intracranial epidural abscess may cause headache, fever, and seizures. If left untreated, spinal epidural abscess may cause back pain, nerve root pain, and paralysis. Complications of epidural abscess include neurological deficits, meningitis, and sepsis. If treated timely, the prognosis for epidural abscess is generally good.

# Diagnosis

## History and Symptoms
A detailed and thorough history from the patient is necessary. Specific areas of focus when obtaining a history from the patient include immunodeficiency, intravenous drug use, spinal procedure, and trauma. Common symptoms of intracranial epidural abscess include headache, fever, and vomiting. Common symptoms of spinal epidural abscess include back pain, weakness, and persistent pins and needles.

## Physical Examination
Physical examination of patients with epidural abscess is usually remarkable for fever, back pain, and generally well appearance, often contributing to misdiagnosis.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of epidural abscess include elevated inflammatory markers, abnormal platelet count, and presence of Staphylococcus aureus. Laboratory results, while helpful, are not diagnostic of epidural abscess. Laboratory findings should supplement clinical and imaging findings to aid in the diagnosis.

## CT
Computed tomography may be helpful as a secondary method of imaging in the diagnosis of epidural abscess. If MRI is not available, CT scan may serve as the primary imaging technique. Findings on CT scan suggestive of intracranial epidural abscess include the appearance of a crescent-shaped, hypodense, extraaxial lesion or a lens.

## MRI
MRI may be helpful in the diagnosis of epidural abscess, as it is the preferred imaging study. Epidural abscess appearance varies depending on the location of the disease. On MRI, intracranial epidural abscess appears as a lentiform or crescent-shaped fluid collection. On T2-weighted images, epidural abscesses appear hyperintense compared to the cerebrospinal fluid. On T1-weighted images, epidural abscesses appear isointense or hypointense when compared to the brain. Following administration of gadolinium contrast, the dura mater is enhanced on T1-weighted images. On MRI, spinal epidural abscess is characterized by low or intermediate intensity on T1-weighted MR sequences and high or intermediate intensity on T2-weighted images.

## Other Imaging Findings
X ray is likely not helpful in the diagnosis of epidural abscess. Myelography may be helpful in the diagnosis of epidural abscess, however it is now considered obsolete.

## Other Diagnostic Studies
Lumbar puncture is likely not helpful in the diagnosis of epidural abscess. Cerebrospinal fluid study is not routinely performed because it offers little information, and has high associated risks. It should be analyzed only when myelography is performed.

# Treatment

## Medical Therapy
Epidural abscess is generally a medical emergency and requires prompt treatment. The treatment of epidural abscess generally involves a combined medical and surgical approach. Antimicrobial therapy for intracranial epidural abscess includes metronidazole, a third generation cephalosporin, and either penicillin or vancomycin. Antimicrobial therapy for spinal epidural abscess includes vancomycin, cefepime, ceftazidime, and meropenem.

## Surgery
A combination of surgical drainage and prolonged systemic antibiotics (6-12 weeks, IV followed by PO) is the mainstay of therapy for both intracranial and spinal epidural abscess. Due to the importance of preoperative neurologic status, along with the unpredictable progression of neurologic impairment, for the neurological outcome of the patient, surgical therapy varies depending on the location of the abscess. In intracranial epidural abscess cases, burr hole placement or craniotomy should occur as early as possible. In spinal epidural abscess cases, decompressive laminectomy and debridement of infected tissues should occur as early as possible.

## Primary Prevention
Effective measures for the primary prevention of epidural abscess include rapid treatment of inflammatory diseases of the head, prevention of trauma, and decreased IV drug use.

## Secondary Prevention
Secondary prevention strategies following epidural abscess include treatment and management of existing infection.