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British Medical Books Health Issues Computerized Tomography

Pathology

  • metaphyses & cartilaginous end plates - starting areas for blood-borne infections
  • in adults > 30 years the intervertebral disc receives its nutrition from tissue fluids rather than from direct blood supply

Blood supply

  • arterial supply to the vertebrae
    • vertebral artery, intercostal artery, or lumbar arteries provide nutrient vessels that enter the vertebral body
    • posterior spinal branch arteries enter the spinal canal through each neural foramen & separate into ascending and descending branches that anastomose with similar branches at each level
  • intervertebral disc is centrally avascular & dependent on diffusion for its nutrition
  • pelvic veins drain into the spinal venous plexus - frequent metastasis of pelvic tumours & infections to the spine

Mechanism

  • iatrogenic infection - usually through surgical manipulation directly or percutaneously
  • local spread from contiguous structures
    • from the colon via subphrenic abscesses
  • arterial spread of pyogenic bacteria
    • most common method
    • originates in the end plate of the vertebra or in the vertebral body itself
    • spreads to the disc secondarily as the infection progresses
      • bacterial infections rapidly attack the intervertebral disc
      • TB & non bacterial infections preserve intervertebral disc

Aetiology

Organism

  • Staphylococcus aureus & S.epidermidis most common in pyogenic infection (60%)
    • increase in the resistant strains of the organism
  • intravenous drug users commonly infected w/ Pseudomonas aeruginosa
  • Mycobacterium tuberculosis is the most common nonpyogenic infecting agent

Cause

  • spinal surgery is the most common cause of iatrogenic disc infection
  • genitourinary infection most common predisposing factor for blood-borne infection
  • respiratory and dermal infections are less frequently implicated
  • decreased natural immune response
    • diabetes, alcoholism, rheumatoid arthritis
    • chronic renal disease
    • AIDS

Site

  • vertebral end plate > disc space > epidural abscess formation > paraspinal abscess
  • thoracic & lumbar spinal vertebrae - most common areas of pyogenic infection
  • thoracolumbar junction - TB

Diagnosis
Physical Examination

History

    • recent infection is not uncommon
    • immune-suppressing disease

Symptoms

  • pain most common 85%
    • w/ changes in position, ambulation
    • intensity varies from mild to extreme
  • other symptoms - anorexia, malaise, night sweat, intermittent fever & weight loss
  • spinal deformity late presentation of the disease
  • paralysis is complication - rarely is the presenting complaint

Signs

  • temperature elevation usually minimal
  • localised tenderness
  • paraspinal spasm
  • limitation of motion of the involved spinal segments
    • torticollis
    • bizarre posturing
  • other possible findings
    • Kernig's sign, hamstring spasm & generalised weakness
    • abscess formation
  • neurologic signs
    • most frequent w/ infections in the cervical & thoracic areas

Investigations

Bloods

  • FBC, diff.count
  • ESR, CRP
  • culture
  • skin testing

X-ray

  • from 2 weeks to 3 months after the onset of the infection
    • disc space narrowing, vertebral end plate irregularity or loss of N contour of the end plate
    • periosteal reaction & hypertrophic (sclerotic) bone formation
    • paravertebral soft tissue masses
  • late findings - vertebral collapse, segmental kyphosis & bony ankylosis

Radionuclide scanning

  • effective in identifying spinal infection
  • techniques include
    • technetium 99 (Tc-99m) bone scan
    • gallium 67 (Ga-67) scan
    • indium 111-labelled leukocyte (In-111 WBC scan)
  • false-positive results in neoplastic, non-infectious inflammatory lesions

Computed tomography

  • identifies paravertebral soft tissue swelling & abscesses
  • monitor changes in the size of the spinal canal
  • findings w/ CT scanning are similar to those with plain roentgenograms
    • lytic defects in the subchondral bone
    • destruction of the end plate with irregularity or multiple holes
  • post-myelogram CT
    • defines compression of the neural elements by abscess or bone impingement

MRI

  • accurate & rapid method for identifying spinal infection
  • identifies infected & normal tissues & best determines the full extent of the infection
  • does not differentiate between pyogenic & nonpyogenic infections
    • need for diagnostic biopsy

T1-weighted images

    • << signal intensity in the vertebral bodies & disc spaces
    • margin between the disc and the adjacent vertebral body cannot be differentiated

T2-weighted images

    • signal intensity >> in vertebral disc & << in vertebral body
    • paravertebral abscess - areas of increased uptake

Diagnostic biopsy

  • best method of determining infection
  • appropriate antibiotics can be administered
    • administration of AB before biopsy may result in a negative biopsy
  • needle biopsy w/ roentgenographic or CT scan control or open biopsy

Differential Diagnosis

  • primary & metastatic malignancies
  • metabolic bone diseases w/ pathologic fractures
  • infections in contiguous & related structures
    • psoas muscle, hip joint, abdominal cavity & genitourinary system
  • R.A., ankylosing spondylitis & Charcot spinal arthropathy

Non operative treatment

  • usual Rx
  • bed rest & immobilisation
    • body cast or removable body jacket
  • antibiotic treatment
  • according to the positive stains or MC/S
  • time for discontinuing antibiotic therapy
    • iv. antibiotics for about 6 weeks & followed by oral
    • until the ESR returns to normal
    • failure of improvement in the ESR or continued persistence of symptoms should initiate re-evaluation of the therapy, and possibly repeat biopsy or even open biopsy for cultures or to remove sequestered and infected material

Prognosis

    • most spinal infections resolve symptomatically and roentgenographically w/in 9-24/12
    • recurrence of the infection & periods of decreased immune response are always possible
    • delayed complications of kyphosis, paralysis & myelopathy

Indications for surgery

  • progressive neurology on conservative rx.
  • instability of spinal column

Specific infections

Pyogenic Infections

  • males > females
  • adults > children
    • peak ages between 45-65 years
  • most common organism reported is S. aureus

Infections in children

  • syndrome of discitis(vertebral osteomyelitis)
  • average age of onset 6-7 yrs
  • characterised by fever & >> ESR
  • followed by disc space narrowing on plain X-rays
    • frequently difficulty in walking, malaise, irritability
    • most culture reports are positive for S. aureus
    • in children younger than 6 years of age may be viral in origin

diagnosis difficult initially

    • plain roentgenograms usually negative
    • may be a mild febrile reaction, but patients do not appear systemically ill
    • only an elevated ESR
    • best test either MRI scanning or a combination of bone scanning & gallium scanning
    • blood cultures helpful if obtained during the initial febrile period of the illness

treatment

    • bed rest and immobilisation
    • diagnosis confirmed w/ blood cultures - intravenous AB
    • surgical procedures rarely are required

Disc space infection in adults

  • in adults intervertebral disc avascular - can't occur by a blood-borne route

surgical manipulation

    • incidence of disc space infection after disc surgery range from 1% to 2.8%
    • after discography 1% w/ single-needle technique 0.5% with the double-needle tech
    • infecting organism is S. aureus

diagnosis difficult and is almost always delayed

    • pain most common complaint
    • diagnostic studies - ESR, bone scan & gallium scan positive 4-6 weeks after surgery
    • MRI the best way to identify
    • biopsy - closed or open
  • Rx: specific or empiric antibiotics

Epidural space infection

    • low reported incidence - increased in immunosuppressed patients
    • morbidity and mortality are high
    • may complicate a primary disc space infection
    • the infection frequently spans three to five vertebral segments, even whole canal
    • S. aureus is the most common

clinical findings

  • several distinct differences:
    • a more rapid development of neurologic symptoms (days instead of weeks)
    • a more acute febrile illness
    • signs of meningeal irritation, including radicular pain w/ positive straight leg-raising test and neck rigidity
    • MRI is critical to the determination
  • treatment
    • surgical drainage and appropriate antibiotic therapy

Brucellosis

    • results in a noncaseating, acid-fast, negative granuloma
    • caused by a gram-negative capnophilic coccobacillus
    • individuals involved in animal husbandry and meat processing

symptoms

    • polyarthralgia, fever, malaise, night sweats, anorexia & headache
    • psoas abscesses are found in 12% of patients
    • bone involvement, most frequently the spine, occurs in 2-30% of patients

X-ray

    • steplike erosions of the margin of the vertebral body require 2 months to develop
    • disc space thinning and vertebral segment ankylosis by bridging
  • CT scans and MRI - may show soft tissue involvement
  • brucella titers of 1:80 or greater; confirmatory cultures

treatment

  • antibiotic therapy for 4 months and close monitoring of the brucella titers

Fungal infections

    • noncaseating, acid-fast, negative infections
    • usually occur as opportunistic infections in immunocompromised patients
    • development of symptoms usually is slow
    • pain is less prominent as a physical symptom than in other forms of spinal osteomyelitis
    • laboratory and roentgenographic findings are similar to those of pyogenic infections

Diff.dg

    • tubercular infection
    • tumours
  • direct culture by biopsy is the only method of absolute determination
  • Aspergillus and cryptococcal infections are of special note