Epidural Abscess

Definition

 

Pus collection in the epidural space

 

Epidemiology

 

Usually haemotogenous seeding

 

Very rare

- 37 / 1 000 000 patients with LBP

- 1 /10 000 admissions

- most common in old men

 

Average age 68 years

 

3/4 males

 

Rare in paediatrics

 

Mortality > 12%

 

Risk Factors

 

IV drug abuse

Remote infection / UTI

Alcoholics

Invasive spinal procedures / Epidurals

Spinal instrumentation

Immunosuppression

- DM / RA / CRF / Transplant / CA /HIV

Blunt trauma / vertebral fracture

 

Relhsaus et al Neurosurg Rev 2000

- meta-analysis of 900 cases epidural abscess

- most common risk factors DM / trauma / IVDU / alcoholism

- 5% had had an epidural

- skin infection / abscess most common cause

 

Pathology

 

Site

- thoracic spine

- cervical & lumbar spine less common

- spans average of 4 vertebrae

 

May be anterior or posterior to thecal sac

- dorsal thoracolumbar spine 

- ventral 2° vertebral OM / more common in cervical spine

 

Microbiology

- S aureus 60%

- Streptococcus 10%

- E coli 20% (IVDU, UTI)

- TB

- often unknown

 

Bacterial Route

 

1.  1/2 Haematogenous 

- remote infection

- UTI / Drug abuse 

 

2.  1/4 Direct Spread

- vertebral osteomyelitis

- abscess usually anterior

 

3.  Following Spinal instrumentation / Surgery/ Epidural injection

 

4.  Adjacent foci

 

Abscesses

- psoas / pelvic / retropharyngeal / perinephric

 

1/4 Unknown

 

Spinal Cord Injury

 

1. Direct Compression

- mass effect of pus

- ? causes early symptoms

- pus usually tracks freely in epidural space

 

2. Vascular Occlusion

- decreased arterial flow or epidural vein thrombosis

- responsible for clinical features later in course

- probably more important 

 

Stages

 

1.  Back pain and fever

2.  Radicular irritation

3.  Weakness / sensory deficit / sphincter incontinence

4.  Paralysis

 

Clinical Features

 

Classical triad of

1. Back pain & tenderness

2. Fever

3. Elevated ESR

 

Symptoms

 

Back pain is hallmark

- 95% / usually very severe / may have nerve root pain

- develops over 72-96 hours

 

Cord compression < 50%

- weak / numb / urinary Retention

 

Signs

 

Fever

- present in 2/3

- may be absent with chronic abscess or antipyretics

 

Local Signs

- tenderness

- pain on movement

 

Neurological deficit

- weakness / sensory loss / urinary retention

- may be ambulatory weak / non ambulatory paralysed

- meningitis

 

Investigations

 

ESR

- almost always elevated

- usually~ 100

 

WCC

- usually elevated 

 

Blood Culture

- often identifies organism

 

MRI

 

Investigation of choice

- T1:  Low signal intensity mass 

- T2:  High signal intensity mass

- 85% sensitivity

 

Cervical Epidural Abscess T2 MRICervical Epidural Abscess T1 MRI

 

Gadolinium enhancement T1

- peripherally or homogenous / typical of all abscess on MRI

- increases sensitivity to 95%

 

Assess levels

- multi level epidural pus 

- need multilevel laminectomy and passage of catheter to aid washout

 

Also assess

- vertebral body osteomyelitis

- cord pathology

- other DDx (HNP, tumour, cord infarct) 

 

Bone Scan

 

For non specific symptoms

- fever / malaise

- pyrexia of unknown origin (PUO)

- guides further investigation

 

DDx

 

Initial diagnosis incorrect in 80% patients

- delayed diagnosis typically

 

Mechanical LBP

Vertebral OM

Meningitis

Vertebral metastasis

HNP

Transverse Myelitis

 

Management

 

Issue

 

Mainstain of treatment is diagnosis and treatment before neurology develops

- this gives patient best prognosis

 

Delayed diagnosis most common problem

- 70% patients present with fever and back pain

 

Poor Prognosis

 

Delay in diagnosis

Neurology

Cervical / high thoracic

Diabetes

Immunocompromise

 

Non Operative Management

 

Indication

 

Poor surgical candidates

Complete paralysis > 3/7

No neurology

 

Technique

 

CT guided biopsy

- obtain cultures / guide antibiotic

- aspiration and drainage of collection

 

Antibiotics

 

Treat broad spectrum initially (flucloxacillin + gentamicin)

- 60% S aureus

- 30% Gram negative

- duration of therapy 4 - 8 weeks

 

Operative Management

 

Aims

- decompress cord

- debridement / drainage 

- MCS of organism

- stabilise spine if needed

 

Options

 

1.  Posterior laminectomy

- posterior abscess with no anterior body OM

- washout +++

- leave drain in

 

2.  Anterior vertebrectomy and stabilisation

- severe vertebral OM

 

Prognosis

 

No significant improvement despite medical advances

 

Karikari et al Neurosurgery 2009

- 104 patients treated over 10 years

- mortality 17% in non operative / 23% in operative

- 30% with dorsal abscess were quadriplegic / paraplegic

- 7% in the ventral abscess group

- 11% improvement in non operative group

- 25% improvement in operative group