What are the indications for a CT (computed tomography) scan in patients with suspected neck infections?

Indications for CT in Neck Infections

CT with IV contrast is indicated for suspected neck infections when there are risk factors, abnormal laboratory values, neurological deficits, or when MRI is unavailable or contraindicated. 1, 2

Primary Imaging Recommendations

First-Line Imaging

• MRI without and with IV contrast is the preferred initial imaging modality for suspected neck infections due to:
  • Superior sensitivity (96%) and specificity (94%) 1, 2
  • Excellent tissue characterization and anatomic delineation 1
  • Better visualization of paraspinal and epidural inflammation 1
  • Superior detection of abscesses, fistulas, and soft tissue involvement 2

When CT with IV Contrast is Indicated

1. When MRI is unavailable or contraindicated 1, 2
2. Presence of risk factors:
   • Diabetes mellitus
   • IV drug use
   • Cancer
   • HIV
   • Dialysis 1
3. Abnormal laboratory values (elevated ESR, CRP, leukocytosis) 1
4. Neurological deficits or cauda equina syndrome 1
5. Presurgical planning for suspected infection-related spine instability 1
6. For image-guided biopsy 1
7. When MRI findings are equivocal 1

CT Protocol Considerations

• Always use IV contrast for suspected neck infections 2

  • Increases conspicuity of paraspinal soft tissue abnormalities
  • Enhances visualization of abscess walls
  • Helps detect epidural collections
  • Aids in assessment of thecal sac compression 1

• Do not perform non-contrast CT before contrast-enhanced CT as it adds no diagnostic value 1, 2

Diagnostic Value of CT in Neck Infections

• Sensitivity: 79% for spine infections; lower (6%) for epidural abscesses 1, 2

• Specificity: 100% for spine infections 1

• Accuracy: 63% overall for differentiating abscess from cellulitis 3

• CT is superior for detecting:

  • Early bone changes (within first 2 weeks of infection)
  • Osteolysis and bone erosions
  • Endplate irregularities
  • Spinal canal bony sequestrum 1
  • Gas formation (important for identifying anaerobic infections) 4

Limitations of CT

• Low sensitivity (6%) for epidural abscesses 1
• Limited accuracy (63%) in differentiating abscess from cellulitis 3
• Inferior to MRI for soft tissue characterization 5

Special Considerations

• Gas formation on CT strongly suggests anaerobic infection and is an independent predictor of complications 4

• Specific neck spaces involved correlate with likely pathogens:

  • Submandibular space: Streptococcus species
  • Peritonsillar/parapharyngeal space: Klebsiella pneumoniae (53.1%)
  • Carotid space: Klebsiella pneumoniae (40%) 4

• Predictors of complications requiring more aggressive management:

  • Chronic kidney disease
  • Diabetes mellitus
  • Multiple space infection
  • Gas formation on CT 4

In summary, while MRI without and with IV contrast remains the gold standard for imaging neck infections, CT with IV contrast plays a crucial role when MRI is unavailable or contraindicated, and offers complementary information about bone involvement and gas formation that can guide antibiotic selection and surgical planning.