What are the guidelines for follow-up CT scans in patients with spondylodiscitis?

Guidelines for Follow-Up CT Scans in Spondylodiscitis

MRI remains the imaging modality of choice for follow-up of spondylodiscitis, with CT scans primarily serving as a complementary tool for specific indications. 1

Initial Diagnostic Approach

• MRI with and without contrast is the primary diagnostic modality for spinal infections, with 96% sensitivity, 94% specificity, and 92% accuracy 1
• The MRI protocol should include T1, T2 with fat suppression or STIR sequences, followed by T1 sequences with contrast in axial and sagittal planes 1
• [18F]FDG PET/CT could be the preferred modality for detection of spondylodiscitis within 14 days of symptom onset 2
• In patients with spinal hardware, [18F]FDG PET/CT is recommended, preferably performed 3-4 months after surgery 2

Role of CT in Spondylodiscitis Management

• CT provides valuable information on endplate irregularities, erosions, destruction, and extension to adjacent soft tissues 2
• CT is particularly useful in pre-surgical planning and follow-up of instrumented spine 1
• When spinal fracture is suspected and conventional radiography is negative, CT should be performed 2
• CT findings supportive of infection include endplate irregularities, erosions, destruction, and presence of collections, though these may be absent early in the disease 2

Follow-Up Imaging Guidelines

• Clinical and laboratory parameters (ESR and CRP) should be the primary means of monitoring treatment response 1, 3
• Imaging abnormalities often persist despite favorable clinical and biological response to antibiotic treatment 3
• Persistent imaging abnormalities are not necessarily associated with relapses, neurological sequelae, or persistent pain 3
• Follow-up imaging is not routinely necessary when bacterial spondylodiscitis responds favorably to treatment 3

Specific Indications for Follow-Up CT

• To evaluate spinal stability and fusion status, especially in surgically treated patients 4
• To assess hardware complications in patients with spinal instrumentation 5
• When MRI is contraindicated or unavailable 2
• To guide biopsy procedures when microbiological diagnosis is needed 1, 6

Common Patterns in Follow-Up Imaging

• Decreased disc height is a consistent and early sign that remains stable during follow-up 3
• Vertebral edema, present in 100% of cases initially, may persist in 67% at 3 months and 15% at 6 months 3
• Discal abscesses, initially present in 65% of cases, may persist in 42% at 3 months and 18% at 6 months 3
• Epidural abscesses, present at diagnosis in 30% of cases, typically resolve by 3 months 3

Pitfalls to Avoid

• Relying solely on imaging findings for treatment decisions, as clinical and laboratory parameters are more reliable indicators of treatment response 3
• Unnecessary follow-up imaging when clinical and laboratory parameters indicate favorable response 3
• Delaying treatment while waiting for imaging studies if neurological deficits are present 1
• Using CT as the primary diagnostic tool for epidural abscess due to its low sensitivity (6%) 1

Special Considerations

• Approximately 10% of cases may have non-contiguous multilevel infections, which should be considered in the diagnostic workup 2
• In cases of diagnostic uncertainty, PET-CT with FDG may be useful, especially if MRI is inconclusive or contraindicated 1
• [18F]FDG PET/CT has been shown to change management in 52% of patients with spondylodiscitis 2