Spondylodiscitis (vertebral osteomyelitis) is infection of the vertebral body and intervertebral disc. The most common pathogen is S.aureus (40-60%) reaching via hematogenous spread. The lumbar spine is most commonly affected (50-60%), followed by thoracic (30%) and cervical (10%). MRI is the gold standard diagnostic modality and becomes positive 2-3 weeks before CT. Characteristic MRI findings: T1 low signal in two adjacent vertebral end-plates (replacement of fatty marrow by inflammatory edema), T2/STIR high signal, disc T2 signal increase and enhancement (normal disc does not enhance — the most critical distinguishing finding), end-plate destruction, and paravertebral/epidural collection. CT shows end-plate erosion, disc space narrowing, and paravertebral soft tissue mass. Differentiation from degenerative Modic type I changes is the most challenging differential in clinical practice — diffusion-weighted imaging (DWI) and enhancement patterns aid in differentiation. Diabetes, IV drug use, immunosuppression, chronic renal failure, and recent spinal procedures are major risk factors.
Age Range
40-75
Peak Age
60
Gender
Male predominant
Prevalence
Uncommon
The development mechanism of spondylodiscitis is based on the vascular anatomy of vertebrae and discs. The end-plate regions of vertebral bodies show rich arterial supply — the subchondral arterial network (metaphyseal arteries) runs near end-plates and terminates with arteriolar end-loops. Blood flow in these regions is slowed and turbulent — creating ideal conditions for bacterial settlement during bacteremia. Bacteria arriving via hematogenous spread (most commonly S.aureus, followed by Streptococcus, E.coli, Pseudomonas) settle in the subchondral area and initiate an inflammatory response. Neutrophil infiltration, proinflammatory cytokines (TNF-alpha, IL-1, IL-6), and bacterial toxins destroy end-plate cartilage and subchondral bone — seen as end-plate erosion on CT. The infection crosses the cartilage end-plate to reach the disc: unlike normal conditions, proteolytic enzymes destroy the nucleus pulposus and annulus fibrosus, and the disc shows T2 signal increase (increased water content + inflammatory exudate unlike normal disc). Disc enhancement results from inflammatory neovascularization — the normal adult disc is avascular, but infection triggers new vessel formation. This disc enhancement is the most critical MR finding for differentiating spondylodiscitis from Modic I. T1 end-plate signal decrease reflects replacement of normal fatty marrow (short T1 = bright) with inflammatory edema (long T1 = dark). Epidural and paravertebral collections form from spread of infection to surrounding soft tissues — extending along ligaments and fasciae.
Normal adult disc is avascular so disc does not enhance — disc enhancement indicates inflammatory neovascularization and is the most specific finding for differentiating spondylodiscitis from Modic I.
On T1-weighted sequences, normal fatty marrow signal is lost in two adjacent vertebral end-plates — end-plates appear hypointense (dark). Signal loss typically extends from end-plate toward the vertebral body center. End-plate contour is irregular or lost (destruction). Disc space may be narrowed. This is the earliest MR finding of spondylodiscitis, becoming positive 2-3 weeks before CT.
Report Sentence
T1 signal loss is observed in the end-plates of ...-... vertebral bodies with loss of normal fatty marrow signal; consistent with spondylodiscitis.
On contrast-enhanced T1-weighted sequences, the intervertebral disc shows enhancement — since normal adult disc is avascular, disc does not normally enhance. Disc enhancement is the most specific MR finding of spondylodiscitis and is critically important for differentiation from Modic type I changes. Enhancement is also seen in end-plates. Paravertebral/epidural collection may show rim enhancement.
Report Sentence
Enhancement is observed in the intervertebral disc at ...-... level (normal disc does not enhance), consistent with spondylodiscitis.
CT shows irregular erosion and destruction of vertebral body end-plates — end-plate contour is irregular and destroyed. Disc space is narrowed. Paravertebral soft tissue mass or collection may accompany. In advanced stages, vertebral body collapse (pathological fracture) may develop. CT demonstrates bone destruction better than MRI.
Report Sentence
Irregular erosion of ...-... vertebral body end-plates, disc space narrowing, and paravertebral soft tissue changes are observed, consistent with spondylodiscitis.
On T2-weighted sequences, the infected disc shows hyperintense signal — unlike normal degenerative disc, signal is homogeneously increased. T2/STIR hyperintensity is also seen in end-plates. STIR sequence most sensitively demonstrates inflammatory edema with fat suppression.
Report Sentence
T2 signal increase in the intervertebral disc at ...-... level and T2/STIR hyperintensity in adjacent end-plates are observed, favoring inflammatory/infectious etiology.
DWI diffusion restriction (bright signal, low ADC) in epidural or paravertebral collection confirms purulent content (abscess) — critical for differentiating from phlegmon or reactive fluid. Diffusion restriction may also be seen in end-plates and disc, aiding in differentiation from Modic I.
Report Sentence
Marked diffusion restriction is observed in the paravertebral/epidural collection on DWI (ADC: ... × 10⁻³ mm²/s), favoring purulent collection (abscess).
Criteria
Most common form (80-90%). S.aureus, E.coli, Streptococcus. Early disc involvement, end-plate destruction.
Distinct Features
Rapid onset, fever, leukocytosis, disc space narrowing, small paravertebral collection
Criteria
M.tuberculosis. Disc relatively preserved, large cold abscess, subligamentous spread, skip lesions.
Distinct Features
Insidious onset, anterior vertebral destruction, gibbus deformity, calcified abscess wall, endemic region
Criteria
Infection developing after spinal surgery/procedure. Direct inoculation mechanism. Usually within 2-4 weeks.
Distinct Features
Infection findings around surgical site, may overlap with postoperative changes, contrast MRI critical
Distinguishing Feature
TB preserves disc, large cold abscess, anterior destruction, subligamentous spread, skip lesions; pyogenic spondylodiscitis involves disc early, small collection, skip lesions rare
Distinguishing Feature
Isolated epidural abscess shows no disc/vertebra involvement (may accompany as complication of spondylodiscitis); spondylodiscitis has dominant end-plate and disc involvement
Distinguishing Feature
Vertebral hemangioma T1 bright (fat), polka-dot CT, no disc involvement, no destruction; spondylodiscitis T1 low (edema), end-plate destruction, disc involvement
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthLong-term antibiotic therapy (6-12 weeks) is the cornerstone of spondylodiscitis treatment. Blood cultures (50-70% positivity) and CT-guided disc/vertebra biopsy when needed are performed for pathogen isolation. Urgent surgical drainage may be required in the presence of epidural abscess due to neurological deficit risk. Surgical stabilization is performed for vertebral instability. Treatment response is monitored with MRI — decreased enhancement and disc signal normalization are healing indicators. Contrast-enhanced MRI is mandatory for differentiation from Modic I.
Long-term antibiotic therapy (6-12 weeks IV + oral) is the cornerstone of spondylodiscitis treatment. Pathogen isolation through blood cultures and CT-guided biopsy is important. Urgent surgical drainage may be required in the presence of epidural abscess due to neurological deficit risk. Surgical stabilization is performed for vertebral collapse and instability. Diabetes, IV drug use, immunosuppression, and recent surgery are risk factors.