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Epidural and Subdural Infections

Author: J Stephen Huff, MD, Associate Professor, Emergency Medicine and Neurology, Department of Emergency Medicine, University of Virginia Health Sciences Center
Contributor Information and Disclosures

Updated: May 11, 2009

Introduction

Background

Epidural and subdural infections are similar in that both are suppurative infections that may cause clinical problems by extrinsic compression of CNS structures. They differ in almost all other ways. Both are uncommon and are often discovered in the course of investigation for other, more common, clinical entities.

Approximately 90% of epidural infections are located along the spinal neuraxis and cause symptoms referable to the spinal cord. Intracranial epidural infection frequently is associated with a subdural infection. In contrast, 95% of subdural infections are located intracranially with a predilection for frontal lobe involvement.¹

For purposes of this discussion, epidural infection is considered synonymous with spinal epidural abscess, and subdural infection is considered synonymous with intracranial subdural empyema.

Pathophysiology

Epidural infection, by definition, involves the epidural space between the bone and dura. This is a true space in the spinal canal that posteriorly is filled with epidural fat, small arteries, and a venous plexus. Infections tend to spread over several vertebral levels. Anteriorly, the spinal epidural space is a potential space because the dura adheres tightly to the vertebral body. Abscesses are more frequent in the larger posterior epidural space.

Hematogenous spread with seeding of the epidural space is the suspected source of infection in most children and is thought to occur in many adult cases as well. Reported sources of seeding are numerous and include endocarditis, infected indwelling catheters, urinary tract infections, abdominal infections, and others. Direct extension of infection from vertebral osteomyelitis occurs in adults but rarely in children. A source of infection is not identified in many patients. Spinal epidural abscess following epidural steroid injection and epidural catheter placement has been reported.²

Subdural infections (eg, subdural empyema) occur beneath the dura. Infection spreads over the brain and may penetrate into the parenchyma of the brain or may cause diffuse cerebral edema.

Frequency

United States

Epidural abscesses seem to be increasing in frequency, possibly related to an increase in intravenous drug abuse or an increase in spinal operative procedures. Reported incidence ranges from 0.2-1.2 cases per 10,000 hospital admissions up to 12.5 cases per 10,000 admissions at a tertiary care center.⁴ A recent population study of spontaneous epidural abscess in Olmsted County, Minnesota, found the incidence to be 0.88 cases per 100,000 person-years.⁵

No clear estimate of frequency for subdural empyema exists, but it is uncommon. Subdural empyema is said to account for 15-25% of pyogenic intracranial infections. Extrapolating from frequency figures for brain abscess yields roughly 1-2 cases per 10,000 admissions to a tertiary care center.

Mortality/Morbidity

• Spinal epidural abscesses are, in themselves, not fatal. However, with complications and associated conditions, mortality rates of 5-23% are reported.¹ Paraplegia or quadriplegia is a frequent sequela. Disability seems related to severity and duration of symptoms prior to institution of therapy.
• Most case series of subdural empyema report mortality in the 30% range. Some reviews note a declining mortality rate in recent years.⁶ About 40% of survivors develop a seizure disorder. This disorder was uniformly fatal in the preantibiotic era.

Sex

• No predilection exists with epidural abscess.
• In subdural empyema, men are 3-4 times more commonly affected than women.

Age

• Spinal epidural abscess may be found in all age groups; on average, patients are older than 50 years. Intravenous drug users with spinal epidural abscesses are, on average, aged 35 years.
• Subdural empyema may occur at any age but is most frequent in the second and third decades of life.

Clinical

History

• Spinal epidural abscess
  • Early presentations may be subtle, and diagnosis may be difficult, if not impossible, at early stages.
  • History of fever is often but not invariably present.
  • Localized back pain may be present.
  • Neurologic deficit is consistent with a spinal cord syndrome.
  • History may suggest a source or cause of infection (eg, soft tissue infection, intravenous drug abuse, recent epidural injections, neurosurgical procedures or other instrumentation).
  • Duration of symptoms is typically a few days but may extend over weeks. Symptom onset may also be abrupt.
  • Radicular pain consistent with nerve root irritation may be present and confound evaluation, particularly if the pain occurs in the abdomen or the chest.
  • Progressive sensory disturbances in the extremities, weakness, and incontinence suggest progression to spinal cord involvement.
  • An immunosuppressive condition, such as diabetes, alcoholism, or HIV infection, is often present.
• Subdural empyema
  • Headaches may be initially unilateral but then become generalized.
  • Fever and vomiting may be present.
  • Focal or generalized seizures may be present.
  • Tempo of clinical course usually is fulminant with rapid deterioration.
  • Uncommon indolent courses may follow neurosurgical procedures.
  • A history of recent sinusitis or otitis media may be present.
  • Antibiotic therapy may lessen systemic symptoms.

Physical

Both spinal epidural abscess and subdural empyema may manifest generalized signs and symptoms of infection such as fever, sepsis, or septic shock.

• Spinal epidural abscess
  • Localized tenderness to percussion or palpation over the involved region may be present.
  • Signs of spinal cord dysfunction, such as loss of sphincter tone, sensory loss, or localized motor weakness, may be present.
  • Reflexes may vary from hypoactive or absent to brisk and spastic.
• Subdural empyema
  • Focal neurologic deficit or focal seizures may be present in a patient with signs of meningeal irritation.
  • Altered mental status is present in most patients.
  • Focal neurologic signs, such as hemiparesis or aphasia, may precede further alteration in consciousness.
  • Papilledema is absent in most patients, reflecting a short duration of increased intracranial pressure.

Causes

• Spinal epidural abscess
  • Most cases arise from hematogenous seeding of the epidural space from a distant source of infection.
  • Another etiology is extension of infection from adjacent vertebral osteomyelitis.
  • Penetrating trauma, recent neurosurgical procedures, or recent epidural injections or catheter placements are other causes.
  • Staphylococcus aureus is the most frequent bacteriologic cause, with methicillin-resistant S aureus (MRSA) being increasingly reported.
• Subdural empyema
  • Most cases are extensions of infections from the paranasal sinuses.
  • Otitis media or mastoiditis also may extend into the subdural space.
  • Recent neurosurgical procedures and penetrating trauma cause other cases.
  • Hematogenous spread of infection from a pulmonary source also has been reported.

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