◊Most common pediatric spine problem!

Etiology:

1. Bloodborne bacterial invasion of vertebrae infecting disk via communicating vessels through endplate
   • Vertebral osteomyelitis + diskitis may be the same entity!
2. Invasive procedure / trauma: surgery, diskography, myelography, chemonucleolysis
3. Extension of adjacent infection

Organism:

1. pyogenic: Staphylococcus aureus (>50%), gram-negative rods (in IV drug abusers / immunocompromised patients)
2. nonpyogenic: tuberculosis, coccidioidomycosis
   • TB has a propensity to extend beneath longitudinal ligaments with involvement of multiple vertebral levels

Pathogenesis: infection starts in disk (still vascularized in children) / in anterior inferior corner of vertebral body (in adults) with spread across disk to adjacent vertebral endplate

Age peaks: 6 months to 4 years; 10–14 years; 6^th–7^th decade

• over 2–4 weeks gradually progressing irritability, malaise, low-grade fever; refusal to bear weight; myelopathy
• neck / back / referred hip pain, limp, focal tenderness
• elevated sedimentation rate, WBC count often normal
• positive blood culture (in 58%)

Location: L3-4, L4-5, unusual above T9

Distribution: 2 adjacent vertebrae + intervening disk

Plain film (positive 2–4 weeks after onset of symptoms):

• decrease in disk space height (earliest sign) = intraosseous herniation of nucleus pulposus into vertebral body through weakened endplate
• indistinctness of adjacent endplates with destruction
• endplate sclerosis (during healing phase beginning anywhere from 8 weeks to 8 months after onset)
• bone fusion (after 6 months to 2 years)

CT (SAG / COR reformatted images more sensitive!):

• early loss of disk height
• endplate irregularities ← destruction
• vertebral body collapse
• paravertebral inflammatory mass / abscess
• epidural soft-tissue extension with deformity of thecal sac

MR (preferred modality; 93% sensitive, 97% specific, 95% accurate):

• Very sensitive modality early on in disease process!
• ↓marrow intensity on T1WI in 2 contiguous vertebrae
• signal intensity of disk decreased on T1WI + increased on T2WI compared to skeletal muscle
  • Fluid-sensitive sequence with fat suppression!
• progressive destruction of vertebral body
• in early stage preserved disk height with variable intensity on T2WI (often increased)
• in later stages loss of disk height with increased intensity on T2WI (= intradiskal fluid)

CEMR:

• focal enhancement of involved disk + adjacent vertebral endplates ± bone marrow

NUC (41% sensitive, 93% specific, 68% accurate on ^99mTc-MDP + ^99mTc WBC scans):

• positive before radiographs
• increased uptake in vertebral endplate adjacent to disk
• bone scan usually positive in adjacent vertebrae (until age 20) ← vascular supply via endplates; may be negative after age 20

Dx: needle biopsy (77% positive) before IV antibiotics

Cx:

1. epidural / paravertebral abscess ← extension of infection
2. kyphosis

Rx: immobilization in body cast for ~ 4 weeks

DDx: neoplastic disease (no breach of endplate, disk space often intact)