eMedicine Specialties > Infectious Diseases > Skin and Soft-Tissue Infections

Epidural Abscess

Author: Mark Raymond Wallace, MD, Infectious Disease Fellowship Director, Orlando Regional Healthcare; Clinical Professor of Medicine, Florida State University
Coauthor(s): Aadia Rana, MD, Research Fellow, Department of Medicine, Division of Infectious Diseases, The Miriam Hospital, Brown University School of Medicine; Gopala K Yadavalli, MD, Associate Program Director of Internal Medicine, Assistant Professor of Medicine, Division of Infectious Diseases, Case Western Reserve University School of Medicine and Louis Stokes Cleveland Veterans Affairs Medical Center
Contributor Information and Disclosures

Updated: Apr 20, 2009

Introduction

Background

An epidural abscess is a rare but potentially life-threatening disease that requires early detection and prompt management. It is defined as an inflammation that involves a collection of pus between the dura (the outer membrane that covers the brain and spinal cord) and the bones of the skull or spine. Spinal epidural abscess (SEA) and intracranial epidural abscess (IEA) are the two types of epidural abscess, and the difference is based on where they develop within the CNS and some variations in risk factors (see Pathophysiology) and symptoms (see History).

A loose association between the dura and vertebral bodies enables extension of spinal epidural abscess to numerous levels, frequently resulting in extensive neurological findings and often necessitating multiple laminectomies. The lumbar and thoracic spine are more commonly affected than the cervical spine.

Tight adherence of the dura to the skull limits expansion of intracranial epidural abscess, often resulting in dangerously increased intracranial pressure, which is a neurosurgical emergency.

Early recognition of these diseases and timely consultation with a neurosurgeon and infectious disease specialist is vital to optimizing the neurological outcome.

Pathophysiology

Spinal epidural abscess

Causes of spinal epidural abscess^1,2,3

• Ten to thirty percent of spinal epidural abscesses result from direct extension of local infection, usually vertebral osteomyelitis, psoas abscess, or contiguous soft-tissue infection.
• About half are due to hematogenous seeding. The most likely source is a soft-tissue process, but anything capable of causing bacteremia can result in spinal epidural abscess (endocarditis, urinary tract infection, respiratory tract infections, intravenous drug use, vascular access devices). Hematogenous seeding of the spinal epidural abscess can result in multilevel noncontiguous spinal epidural abscess.
• Fifteen to twenty-two percent of spinal epidural abscesses are due to invasive procedures or instrumentation. Spinal surgery, epidural anesthesia, steroid and pain-relieving injections, and placement of pain pumps are all associated with spinal epidural abscess. Short-term epidural anesthesia is obviously much less risky than a catheter left in place for days or permanently implanted.
• In some cases (up to 30% in some series), the source of the spinal epidural abscess is not identified.

Risk factors for spinal epidural abscess^4,5,1,2  

• The most common risk factor for spinal epidural abscess is diabetes mellitus, followed by spinal trauma (may be remote) or surgery, intravenous drug abuse, alcoholism, renal insufficiency, immunosuppression (including HIV infection and malignancy), and spinal/epidural injections.
• Intravenous drug use seems to represent an increasing risk factor in many series.

Anatomy of spinal epidural abscess^2,1

• Most abscesses occur posteriorly. An anterior location is often associated with vertebral osteomyelitis.
• The thoracic and lumbar areas are the most likely sites of involvement, with the cervical spine accounting for approximately 20% of cases.⁵
• Spread to multiple vertebral levels is common and occurs as the abscess extends up and down the spinal dural sheath. In some cases, this process involves most or all of the spine.

Mechanism of injury¹

• Direct compression of the cord is clearly a major factor.
• Vascular occlusion due septic thrombophlebitis and/or vasculitis is also a factor
• The exact mechanism of injury remains controversial.

Intracranial epidural abscess

• Because intracranial epidural abscess can cross the cranial dura along emissary veins, an accompanying subdural empyema is often present.⁶
• Risk factors for intracranial epidural abscess include prior craniotomy, head injury, sinusitis, otitis media, and mastoiditis.^7,6

Frequency

United States

The annual incidence of spinal epidural abscess has risen in the past 2-3 decades from 0.2-1 cases per 10,000 hospital admissions to 2.5-3 per 10,000 admissions.¹ The rising incidence of spinal epidural abscess has been attributed to the increasing prevalence of injection drug use, as well as to an increased performance of invasive spinal procedures.

The annual incidence of intracranial epidural abscess is difficult to determine but is recognized to be much less common than spinal epidural abscess.

International

Few data on epidural abscesses are available outside the United States, but the frequency appears to be similar to that in the United States.

Mortality/Morbidity

• Spinal epidural abscess: At the beginning of the 20th century, almost all individuals with spinal epidural abscess died. However, associated mortality rates have dropped significantly over the past 50 years, likely because of better diagnostic modalities. Nonetheless, despite advances in imaging and surgical care, the current mortality rate ranges from 2%-20%.^2,1,5 Not surprisingly, the mortality risk is greater in those with severe underlying comorbidities or uncontrolled sepsis. Differences in etiology (ie, iatrogenic vs noniatrogenic) do not affect the prognosis. The essential problem of spinal epidural abscess lies in the necessity of early diagnosis, as permanent neurological deficits and possible mortality can be avoided or reduced only with timely treatment.
• Intracranial epidural abscess: With antibiotic and surgical management, intracranial epidural abscess carries a good prognosis, with an attributable mortality rate of less than 10%.
• The neurological status of the patient at the time of diagnosis is the best predictor of neurological outcome, and morbidity is increased in both conditions when indicated surgery is delayed.^7,1,2

Sex

Most studies report that epidural abscess is more common in males than in females.

Age

• Spinal epidural abscess can occur at any age. The median age of onset of spinal epidural abscess is approximately 50-60 years.
• Intracranial epidural abscess is most common in the second and third decades of life.

Clinical

History

• Spinal epidural abscess^5,1
  • Most symptoms of a spinal epidural abscess are due to enlargement of the abscess and surrounding inflammation, which can lead to tissue compression and spinal cord ischemia. Onset of symptoms usually occurs within hours to days but may be more chronic in nature, presenting with weeks to months of symptoms. The microbiology often dictates the pace of progression.¹
  • Back or neck pain is the most common symptom in individuals with spinal epidural abscess, occurring in 70%-100% of cases.
  • The classic diagnostic triad of fever, spinal pain, and neurological deficits is present in only 10-15% of cases at first physician contact and must not be relied on for diagnosis.
  • If left untreated, the progression of symptoms is usually sequential and forms the basis for the staging of spinal epidural abscess (see Staging): (1) back pain; (2) radicular irritation; (3) motor weakness, sphincter dysfunction, sensory changes; and, finally, (4) paralysis. Note that this progression may occur very rapidly, and some symptoms may be skipped.
  • The patient's neurological status at the time of diagnosis is the most accurate predictor of outcome and prognosis.
• Intracranial epidural abscess^7,6
  • The symptoms of intracranial epidural abscess are generally more acute but may be difficult to discern from the inciting process (eg, sinusitis, postoperative infection). When intracranial epidural abscess is combined with a subdural empyema, as is often the case, the course is compressed.
  • Signs and symptoms are due to both infection and the slowly expanding intracranial mass. Fever, headache, malaise, lethargy, nausea, and vomiting may be present. Intracranial epidural abscesses due to sinus infections can cause purulent drainage from the nose or ear.
  • Patients without a history of recent cranial manipulation who develop intracranial epidural abscess present with encephalopathy and focal neurological deficits. Most patients who have undergone craniotomy (67%) tend to be afebrile at presentation, and their neurological deficits are often less severe and less acute, with more than 90% showing evidence of wound infection.

Physical

• Findings associated with spinal epidural abscess from multiple studies include the following:¹
  • Fever (range, 13%-95%; median, 32%) (However, note that many patients with spinal epidural abscess are afebrile.)
  • Spinal tenderness (range, 17%-98%; median, 58%)
  • Weakness of the extremities (range, 26%-87%; median, 40%)
  • Sensory abnormalities (range, 13%-45%; median, 36%)
  • Paralysis (range, 5%-39%; median, 27%)
  • Reflex abnormalities (up to 40% of cases) (Early hyperreflexia may give way to diminished or absent reflexes.)
  • Respiratory compromise (with cervical lesions)
• Findings associated with intracranial epidural abscess include the following:^7,6
  • Fever (However, fewer than half of patients are febrile, so this symptom is unreliable.)
  • Headache (50%-73%)
  • Altered mental status (44%-50%)
  • Sinus tenderness (32%-90%)
  • Focal neurological deficits
  • Evidence of wound infection (>90% of patients who have undergone craniotomy)
  • Seizure (4%-63%)

Causes

The microbiologic causes of spinal epidural abscess and intracranial epidural abscess are considered separately.

• Staphylococcus aureus infection causes most cases of spinal epidural abscess. This is followed in frequency by streptococcal and Enterobacteriaceae infections. Coagulase-negative staphylococcal infections are observed almost exclusively in the context of recent spinal instrumentation or other medical procedures. The most common organisms that cause spinal epidural abscess include the following:^5,1
  • S aureus (60%; increasingly often methicillin-resistant S aureus [MRSA])
  • Enteric gram-negative bacilli, especially Escherichia coli (10%)
  • Coagulase-negative staphylococci (3-5%), primarily involving spinal instrumentation or epidural anesthesia/injections
  • Bacteroides species and other anaerobes (2%)
  • Pseudomonas species (2%)
  • Streptococci, including Streptococcus viridans, group B streptococci, and pneumococcus (10%)
  • Mycobacteria, usually Mycobacterium tuberculosis (<1% in Western countries but more common in developing countries)
  • Less-common organisms -Acinetobacter , enterococci, Actinomyces species, Nocardia species, Brucella species, and fungi, including Candida, Coccidioides, Aspergillus, Blastomyces, and Sporothrix species
  • Polymicrobial (possibly 5%-10%)
  • Unknown (6%-10%)
• In intracranial epidural abscess, upper-respiratory bacterial pathogens predominate in sinus-associated disease, whereas nosocomial pathogens are of concern in cases that develop after craniotomy. The most common causative organisms include the following:
  • Staphylococci, both coagulase-positive and coagulase-negative
  • Streptococci, including anaerobic and microaerophilic species
  • Aerobic gram-negative bacilli
  • Propionibacterium acnes
  • Other anaerobes
  • Can be polymicrobial

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