Infection

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

 

 

Postoperative Infection

Incidence

 

Decreasing incidence in recent decades most likely attributable to preoperative antibiotics

 

Ris

 

Conventional discectomy </= 1%

Fusion 2%

Fusion & instrumentation 5-6%

 

Instrumentation doubles infection rate in lumbar fusion

 

Risk factors 

 

Diabetes 

Poor nutritional status

Rheumatoid arthritis

Steroid use 

History of previous infection

Previous wound irradiation

 

MRI

 

Cervical Post op Abscess

 

Options

 

Aggressive wound debridement of devitalised tissue with adequate drainage mandatory

- may leave open & packed

- antibiotic loaded beads 

- removal of hardware may leave spine unstable

 

Postoperative discitis

SymptomsT45 discitis

 

Period of pain relief after disc surgery

- followed by increasing back pain & occasional leg pain

 

Pain may be disproportionate to physical findings

 

Low grade fever common

 

SLR & femoral stretch tests elicit pain in some cases 

 

Bloods

 

Normal WCC common 

ESR & CRP elevated 

 

Xray / MRI

 

Discitis XrayDiscitis MRI

 

MRI with Gadolinium

 

Investigation of choice

- well vascularized inflammatory tissue enhances on T1

 

MRI Gadolinium Post Operative Discitis T1MRI Gadolinium Post Operative Discitis T2

 

Osteomyelitis changes include

- confluent hypointensity of involved bodies on T1

- hyperintensity of involved bone and disc on T2

- loss of distinction of involved bone & disc

- abnormal disc appearance

 

Management

 

Medical management

 

CT guided aspirate if culture required

- appropriate antibiotics

- brace

 

Surgical Indications

 

Failure non operative management

Epidural abscess

Deformity

 

Post Op Discitis with Deformity

 

Options

 

1.  Percutaneous Discectomy and Drainage

 

Li et al Arch Orthop Trauma Surg 2011

- 31 patients with post-operative discitis

- half had positive cultures, other half sterile

 

2.  Laminectomy and Drainage

Spinal Tuberculosis

Epidemiology

 

Most common site for skeletal TB

- usually haematogenous spread

- can be direct from lung

 

3 patterns

 

1.  Peridiscal (50%) - originating in metaphyseal region

2.  Central - high incidence of vertebral collapse

3.  Anterior - instability less common with less bony destruction

 

Pathology

 

Affects multiple contiguous vertebrae

- starts anterior 1/3 vert body

- doesn't stay within body

- spreads along fascial planes

- spreads under ALL

 

More likely to produce kyphosis

 

Disc sequestered rather than destroyed

 

Posterior elements frequently involved unlike pyogenic

 

Xray

 

Short kyphotic deformity

- known as Gibbus Deformity

 

DDx

 

May be mistaken for neoplasia

 

Similar Xray appearance 

- brucellosis, hydatid disease

- fungus (aspergillosis / Cryptococcus / candidiasis)

 

Prognosis

 

Age influences risk of paralysis

 

Cervical in patient younger than 10 years

- 17% risk of cord injury

 

Cervical in patient older than 10 years 

- up to 81% risk of paralysis

 

Management

 

Non operative

 

British Medical Research Council

- 77% settled with drug treatment alone

- no patients with neurology / paralysis

- drug treatment for 12/12

- spontaneous fusion can be expected

 

Operative

 

Indications for Surgery

 

1.  Deformity

- kyphosis

- >50% verterbral body destruction

 

2.  Neurology

 

3.  Biopsy

 

4.  Failure nonoperative treatment

 

Technique

 

Hong Kong Procedure

- debridement of infected bone

- decompression of spinal canal

- correction of kyphotic deformity using structure grafting

- instrumentation

 

Vertebral Osteomyelitis

Epidemiology

 

M:F =2:1

 

30-40 years

 

20% diabetic

 

50-80% identifiable source

 

Site

 

Lumbar (50%) > Thoracic > Cervical (<10%)

 

Pathogenesis

 

1.  Haematogenous

- arterial rather than venous

 

Risk factors

- UTI (40% of all cases)

- IVDU

- elderly

- respiratory infection

- immunocompromised

- DM

 

2.  Direct spread

- pelvis or psoas

- percutaneous or open spinal procedures

 

Organism

 

Staph aureus 60%

 

Streptococcus

 

Gm negative

- Ecoli, Proteus

- UTI / GUT procedures

 

Salmonella in sickle cell

 

Pseudomonas in IVDU

 

TB / Fungus

- in immunocompromised

- may require life long therapy

 

Patients

 

Elderly

IVDU

Immunocompromised

- steroids

- transplant

- DM, RA

 

Pathology

 

Initial focus at end plates

- septic emboli to end arterial circulation

- series of inter-metaphyseal artery allows infection of contiguous vertebrae

- spreads by direct extension to adjacent vertebrae unlike TB

 

Disc destruction

- disc is avascular 

- allows infection to spread here as well

- forms collection / abscess

 

Deformity

- due to body and disc destruction

- kyphotic

 

Neurology

- compression from epidural abscess

- infarction of regional supply to cord

- pathological fracture fragments

- kyphosis

 

Clinical Presentation

 

Back pain / tenderness + fever + elevated ESR

 

Diagnosis often delayed 4-6/12 due to vague symptoms

 

90% back pain

- insidious, non-mechanical, night pain

- localised tenderness

 

50% fever

 

< 10% neurological deficit

 

Bloods

 

ESR elevated > 90%

- most sensitive test

 

WCC elevated 35%

 

Blood culture's

- often negative

- especially if low virulence

 

Urine culture

 

Malnutrition

- albumin / lymphocyte count

 

X-ray 

 

Changes 4-6/52

 

Findings

- loss of disc height

- end plate irregularities/erosions

- vertebral destruction

- contiguous vertebrae

- collapse usually without severe kyphosis of TB

 

CT

 

Soft tissue involvement

Good for TB 

 

Cervical Osteomyelitis CT

 

Bone Scan

 

Localise area of problem if diagnostic dilemma

 

MRI 

 

Vertebral Osteomyelitis MRICervical osteomyelitis

 

Investigation of choice

- 95% accurate

- diagnose vertebral osteomyelitis

- look for epidural abscess

 

Early

- T1 loss of distinction between disc and end plate

- T2 loss of normal disc intranuclear cleft

- specific for infection

 

Gadolinium T1

- ring enhancement

 

DDx

 

Tumour 

- preservation of disc

 

TB 

- no increased T2 in disc

 

CT guided biopsy 

 

Indication

- If organism unknown

 

Technique

- aspiration if abscess

- bone biopsy otherwise

 

Results

- culture 75% of microbes prior to antibiotics

- only 25% after antibiotics given

 

Open biopsy

 

Indication

- if no CT available / unsuccessful

 

Technique

- posterior approach

- specimen obtained through pedicles 

- T-spine through costotransversectomy

 

Results

- culture aerobic / anaerobic / AFB / fungus

- diagnostic in > 80% cases

 

TB VS Pyogenic

 

Pyogenic                         TB

Single focus                      Multisegments involved

Symmetric collapse           Kyphosis

Spread bone                     Fascial planes

Disc destroyed                  Disc sequestered

Anterior column                All 3 columns (posterior inv)

Epidural abscess               Paravertebral abscess

More acute                       Insidious

 

Management

 

Non-Operative

 

Principles

 

1.  Important to delay antibiotics until cultures taken

- BC's

- urine M/C/S

- CT biopsy

 

2.  After biopsy

- most settle with antibiotics

- 6-8 weeks IV treatment (until ESR norm)

- continue orals 3-6/12

 

3.  Immobilisation important

- Bed rest

- TLSO

 

4.  Adequate nutrition important

- serum albumin

- WCC

- transferrin

 

5.  Spontaneous fusion occurs in 60%

 

Operative Management

 

Indications

 

1.  Biopsy for diagnosis and M/C/S

 

2.  Failure medical management

- systemically unwell

 

3.  Neurological deficit

 

4.  Deformity / instability

 

Anterior approach & corpectomy

 

1.  Adequate debridement crucial

 

2.  Autograft preferred

- iliac crest, fibula, rib

- can use allograft 

 

3.  Instrumentation

- anterior +/- supplemental posterior

 

Results

 

Lu et al Neurosurgery 2009

- review of 36 patients treated with corpectomy + titanium cage

- nearly all patients required anterior + posterior instrumentation

- 2 infection recurrences, 1 each with autograft and allograft

- all had neurological improvement

- 81% pain free