Epidural Abscess: Spinal and Cerebral
Spinal Epidural Abscess
Spinal epidural space is also known as extradural space or peridural space. Epidural space is attached to foramen magnum at the cephalic end and at the caudal end it ends with sacrococcygeal membrane. It is the outermost anatomical space in spinal canal of vertebral column. Circular epidural space is tightly covered by dura mater from inside and contains lymphatics, spinal nerve root, loose fatty tissue, arteries and epidural venous plexus.
Cerebral Epidural Abscess
Cerebral epidural space is anatomically non-existent as dura is closely adhering to skull. Cerebral epidural space is a non-existent potential space, which may emerge with separation of dura from skull in case of abscess formation or appearance of epidural hematoma.
Abscess is collection of pus consisting of dead cells, bacteria, and debris. Abscess occupies space and may cause space occupying lesion and symptoms. Size of abscess determines the space occupied in compact skull and spinal canal. Symptoms could be severe and life threatening. Prompt diagnosis and treatment is essential to prevent death in few cases. It is a rare disease, 0.5 to 1.2 cases per 10,000 hospital admissions per year.
Epidemiology of Epidural Abscess
Epidural abscess is a rare disease. Fifty percent of cerebral and spinal epidural abscess occurs mostly by hematological spread. Thirty percent of epidural abscess is secondary to local spread from infection or abscess within bones, muscles and soft tissue. While remaining 20% epidural abscess occurs during invasive procedures or by spread of abscess metastasis from infected pockets where foreign body are located like invasive implants and intravenous ports or catheter.
Invasive procedures such as intraoperative epidural injection causes epidural abscess with rate of 1 in 2000 cases but on the contrary placement of epidural catheter has a higher rate of epidural abscess like 4.3 cases in 100 cases.
Rate of epidural abscess in hospital admission has increased in last 20 years. One of the main reasons for increased abscess rate is because of increased rate of invasive procedures. In U.S., increase was from 0.5 to 1 case per 10,000 hospital admissions to 2.5 to 3 cases per 10,000 admissions.
Eighty percent of spinal epidural abscess are seen in thoracic and lumbar areas, while cervical epidural abscess accounts for approximately 20% of cases. In various epidemiological studies, diabetes was found to be most common risk factor with occurrence rate of 18- 54 % cases and second most common risk factor was intravenous drug abuse with occurrence rate of 7 - 40%. In some studies, 10% of cases had history of trauma a short period prior to abscess development. Trauma may have caused local extension of infection or hematological spread from hematoma caused by trauma and got infected.
Classification and Types of Epidural Abscess
Classification of epidural abscess:
- Intracranial epidural abscess located within the skull.
- Spinal epidural abscess within vertebral column.
Pathophysiology of Epidural Abscess
Epidural abscess may be located in spinal canal or within skull. Cerebral abscess can be life threatening depending on size and volume. Abscess may be as a result of staphylococcus aureus bacteria as a most common pathogen. S. aureus bacterial infection is observed in infected pocket of device and in hospital infections such as MRSA abscess. Other bacterial infections are Pseudomonas, E. Coli, Brucella and Mycobacterium tuberculosis. Rarely in a few cases the cause of abscess is found to be fungus infection.
Pathophysiology of Cerebral Epidural Abscess:
Cerebral 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 the bones of the skull. Cerebral epidural abscess can cause increased intracranial pressure and ischemic changes of vital centers of brainstem and subcortical nuclei. Space between dura and skull is narrow and outer expansion is limited by thick skull. If abscess developed, the expansion is within the brain tissue and results in early clinical symptoms. Moderate sized abscess can be life threatening. Abscess formation depends on local infection and spread from other sources as described in causes and risk factors.
Pathophysiology of Spinal Epidural Abscess:
Spinal Epidural space is outside dura matter. Dura is attached to foramina magnum at cephalic end. True epidural space is detected only on lateral and posterior side of spinal canal. The epidural space is widest in sacral dermatome and narrow in neck. Spinal epidural abscess in most cases spreads in caudal and cephalic direction. Enlarged spinal epidural abscess causes compression or ischemia of spinal cord. As abscess expands, pressure is transferred to blood vessels, nerves and spinal cord.
Spinal cord receives blood from three longitudinal arteries called anterior spinal artery and two posterior spinal arteries. In addition, there are several other small arteries branched from surrounding arterial supply spinal cord. Ischemic changes of spinal cord are compression of these arteries by massive abscess in epidural space. Alternatively, ischemic changes are also occurring following embolism or thrombosis of these arterial vessels. Pressure or ischemia of nerves in foramina causes segmental neurological impairment causing segmental sensory or motor deficiency. Ischemia or severe pressure of spinal cord in thoracic or lumbar segment will be clinically presented as paraplegia. Cervical epidural abscess can generate increased pressure over spinal cord in neck and initiate symptoms of quadriplegia.
Abscess may spread several levels of vertebral column needing multi level laminectomy surgery. Most common cause of spinal abscess is hematological spread from chronic mastoiditis, boil, hair follicle infection, meningitis, osteomyelitis and otitis media. Most of the spinal epidural abscess occurs in thoracic epidural space. Epidural abscess may be direct spread of infection from osteomyelitis in adults and children. In majority of cases, severe spinal cord injury was observed secondary to compression of blood vessel and ischemia rather than pressure from mass effect. The exact mechanism of injury either by compression of spinal cord or ischemia remains controversial. Recovery after surgery is prolonged and may end with some sensory and motor neurological deficiency. Injury to spinal cord is often secondary to thrombosis of leptomeningeal vessel and spinal artery than compression of spinal cord.
When intracranial epidural abscess is combined with a subdural empyema, as is often the case, the course is compressed.
Causes and Risk Factors of Epidural Abscess
Causes of Spinal and Cerebral Epidural Abscess:
Direct Extension - 30% of abscess by direct spread.
- Local Infection
- Vertebral Column
- Psoas Abscess.
Hematogenous Spread - 50% of abscess can be multilevel and noncontiguous.
- I.V. Drug Abuser.
- Otitis Media.
- Respiratory Tract Infection.
- Urinary Tract Infection.
- Vascular Access Device Infection.
- Infection of Implanted Device - e.g. defibrillator, intrathecal pump, spinal cord stimulator.
Invasive Procedure - 20% of abscess introduced by invasive procedures.
- Spinal Instrumentation Surgery.
- Epidural Anesthesia.
- Spinal Anesthesia.
- Placement Epidural Catheter.
- Placement of Spinal Cord Stimulator.
Risk Factors of Epidural Abscess
- Systemic Diseases
- Compromised Immunity.
- Diabetes Mellitus.
- HIV Infection.
- Infectious Disease
- Chronic Sinusitis Mastoiditis.
- Otitis Media.
- Respiratory Tract Infection.
- Urinary Tract Infection.
- Drug Induced
- Steroid Treatment.
- Infected Pocket of Instrumentation and Implant
- Spinal Fusion Surgery.
- Spinal Cord Stimulator - Spinal and Cerebral.
- Epidural Catheter Placement.
- Shunt Placement.
- Fracture of Skull.
- Vertebral Body Fracture.
Signs and Symptoms of Epidural Abscess
Sex - More common in males than in females.
Age - Spinal epidural abscess is most common in working age between 50 and 60 years. Cerebral epidural abscess is common between age 20 and 30 years.
General Symptoms of Epidural Abscess:
- Generalized Weakness.
Signs and Symptoms of Cerebral Epidural Abscess
Symptoms of Cerebral Epidural Abscess
- Fever is common in most of the cases.
- 67% of cases undergoing craniotomy are afebrile in the initial phase.
- Nausea and Vomiting.
- Disturbed consciousness and change in mental status.
- Surgical Pain - Becomes worst.
- Onset of Symptoms - Acute and Sudden.
- Symptoms like encephalopathy - Alteration in mental status, confusion, memory loss, amnesia, loss of alertness, loss of orientation, disruption of perception, psychomotor skills are disrupted, change in emotional status, confusion and delirium.
Signs of Cerebral Epidural Abscess
- Difficulties with coordination and movement.
- General weakness of the muscles in both the arms and legs that worsens.
- Purulent discharge from ear, if associated with ear infection (otitis media).
- Signs of encephalopathy and focal neurological deficiency as described in symptoms.
- Evidence of wound infection.
Early symptoms of Cerebral Epidural Abscess
- Vomiting and Fever.
Signs and Symptoms of Spinal Epidural Abscess
Onset of early symptoms usually occurs within hours to days. If initial symptoms are ignored, later symptoms such as pain, headache, nausea and vomiting become chronic. 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.
Symptoms of Spinal Epidural Abscess
- Back Pain.
- Bladder and bowel incontinence - Difficulty urinating (urinary retention), inability to control your bowels or bladder.
- Neurological symptoms depend on the location of the abscess and may include:
- Decreased ability to move any part of the body.
- Loss of sensation in any area of the body, or abnormal changes in sensation.
- Weakness feeling very tired and sluggish.
Signs of Spinal Epidural Abscess
- Spinal Tenderness.
- Weakness of the extremities.
- Reflex abnormalities (Early hyperreflexia may give way to diminished or absent reflexes.).
- Respiratory compromise (with cervical lesions).
- Spinal epidural abscess: Bowel and bladder incontinence.
- Difficulty urinating (urinary retention).
- Pain at the site of recent surgery that gets worse (especially if fever is present.
Early Symptoms of Spinal Epidural Abscess
- Spinal Tenderness.
Sequential progression of symptoms if untreated - 4 stages. Progression occurs rapidly, and symptoms may skip or overlap.
- Moderate to severe back pain: Sudden in onset and rapid increase of intensity in short duration.
- Sensorineural deficiency: Radicular pain, tingling and numbness.
- Motor neuro deficiency: Weakness, sphincter dysfunction.
- Paraplegia: Paralysis.
Prognosis of Epidural Abscess
Prognosis depends on early diagnosis. Mild to moderate symptoms are ignored and treated with medication available on pharmacy shelf. Early diagnosis and investigation helps to treat disease appropriately with appropriate treatment. Outcome of early diagnosis and treatment is extremely good. Late treatment after established symptoms such as numbness, weakness and paralysis and numbness may prevent mortality but patient may sustain numbness, weakness or paraplegia.
Complications of Epidural Abscess
Complications of Cerebral Epidural Abscess:
- Brain Abscess.
- Brain Damage.
Complications of Spinal Epidural Abscess:
- Psoas Abscess.
- Chronic Back Pain.
- Spinal Cord Abscess.
Cerebral epidural abscess is much less common than spinal epidural abscess. Present mortality rate of spinal epidural abscess is 2 to 20% as described in different studies. Prior to World War II, several deceased patients were undiagnosed of spinal and cerebral epidural abscess. Many of these patients had postmortem and found to have significant epidural abscess. Over last 40 years, diagnostic modalities for epidural abscess have improved with MRI, CT scan and myelogram. Mortality rate has reduced significantly (2 to 20%) during last 30 to 40 years.
Mortality rate is higher in immunosuppressed patients. Morbidity and mortality is also greater if patient has underlying multiple risk factors. Early diagnosis and timely early treatment has reduced mortality. Morbidity and mortality is higher if at the time of diagnosis patient has developed sensory and motor deficiency.
Differential Diagnoses for Epidural Abscess
Differential Diagnoses for Cerebral Epidural Abscess:
- Brain Abscess.
- Arteriovenous Malformation.
Differential Diagnoses for Spinal Epidural Abscess:
- Herniated Disk.
- Osteomyelitis of Vertebra.
- Psoas Abscess.
- Fever of Unknown Origin.
Tests to Diagnose Epidural Abscess
Tests may include:
- Blood culture and antibiotic sensitivity studies.
- Complete blood count (CBC) - Leukocytosis (increased white blood cell count) was present in only 68% of cases in one series.
- CT Scan of head or spine.
- MRI of head or spine.
- Erythrocyte sedimentation rate was consistently elevated.
- Thrombocytopenia observed in adult and thrombocytosis seen in children.
- Lumbar puncture - Analysis of CSF, culture and antibiotic sensitivity studies.
- Aspirated pus - Tested for pathogens, bacterial culture and antibiotic sensitivity studies.
- Myelography - Demonstrates the presence of a space-occupying lesion. Invasive study is avoided since patient is already infected with abscess formation.
Treatment for Epidural Abscess
The goal of treatment is to cure the infection and reduce the risk of permanent damage.
Antibiotics for Epidural Abscess:
- I.V. for at least 4 - 6 weeks, initial selection of antibiotics against against S. aureus. Later antibiotics are selected after culture and antibiotic sensitivity studies.
- I.V. for 6 to 12 weeks, patient are treated for longer time when not responding to initial treatment.
- Oral antibiotics follow I.V. antibiotics for another 4 to 8 weeks in few cases.
- Choice of antibiotics depends on sensitivity studies and side effects. Antibiotic therapy guided by symptomatic relief, favorable changes in ESR, CAT scan and MRI. Abscess caused by tuberculosis may respond to appropriate antibiotics and surgery may not be necessary.
Percutaneous Drainage of Abscess:
- Mostly performed in children to prevent extensive surgery and postsurgical complication. In most of the cases, needle placement in abscess done under CT guidance.
Surgery for Epidural Abscess:
- Drain abscess.
- Reduce pressure: Craniotomy, laminectomy.
Conservative Treatment for Epidural Abscess:
- Physical therapy
Corticosteroid Therapy for Epidural Abscess:
- Very rarely use in epidural abscess.