CT Neck for Nerve Impingement When MRI is Contraindicated
When MRI is contraindicated, order CT myelography—not contrast-enhanced CT and not non-contrast CT—as the appropriate alternative for evaluating cervical nerve impingement. 1
Why CT Myelography is the Correct Choice
CT myelography achieves 81% diagnostic accuracy for cervical radiculopathy lesions, compared to only 50% for non-contrast CT and 88% for MRI. 1, 2, 3 This makes CT myelography the clear second-line choice when MRI cannot be performed. 3
Key advantages of CT myelography over plain CT:
- Provides superior visualization of the thecal sac and small nerve roots at higher spatial resolution than even MRI 3
- Excellent depiction of foraminal stenosis and nerve root compression, which are the primary pathologies causing radiculopathy 3
- Combines the soft tissue contrast of intrathecal contrast with the bony detail of CT 1
Why Plain CT (With or Without IV Contrast) is Inadequate
Non-contrast CT detects only 50% of cervical radiculopathy lesions—missing half of clinically significant pathology. 1, 2, 3 This unacceptably low sensitivity makes it inappropriate as a substitute for MRI. 3
Critical limitations of plain CT:
- CT excels at visualizing bone (osteophytes, facet joints, uncovertebral joints) but is significantly less sensitive than MRI for detecting nerve root compression from disc herniations 1, 2
- Adding IV contrast to CT does not improve detection of nerve impingement—contrast enhancement does not aid in visualizing neural compression from degenerative disease 1
- CT should be reserved only for detailed bony assessment (e.g., ossification of posterior longitudinal ligament, surgical planning), not for primary evaluation of radiculopathy 2, 3
Procedural Considerations for CT Myelography
Be aware of the invasive nature of this study:
- Approximately 30% of patients experience unexpected adverse reactions to intrathecal contrast injection 3
- About 14% of patients report maximum pain scores (10/10) during the procedure 3
- CT myelography should be reserved strictly for cases where MRI is truly contraindicated (pacemakers, non-MRI-compatible implants, severe claustrophobia), not merely inconvenient 3
Clinical Decision Algorithm
| Clinical Scenario | Imaging Choice | Diagnostic Accuracy |
|---|---|---|
| MRI available and no contraindications | MRI cervical spine without contrast | 88% [1,2] |
| MRI contraindicated (pacemaker, implants, claustrophobia) | CT myelography | 81% [3] |
| Need for detailed bony assessment only (OPLL, surgical planning) | CT without contrast | N/A for nerve impingement [2] |
| ❌ Never use for radiculopathy work-up | Plain CT (with or without IV contrast) | Only 50% [3] |
Common Pitfalls to Avoid
- Do not order contrast-enhanced CT thinking it will improve nerve visualization—IV contrast does not enhance detection of degenerative nerve compression 1
- Do not substitute plain CT for MRI when evaluating radiculopathy, as it misses up to half of relevant pathology and necessitates repeat imaging 3
- Do not order CT myelography as a first-line test—it is invasive with significant patient discomfort and should only be used when MRI is impossible 3
When Plain CT Has a Role
Plain CT without contrast is appropriate only in these specific scenarios:
- Post-surgical patients with hardware complications (assessing fusion integrity, hardware position) 1, 2
- Evaluation of ossification of posterior longitudinal ligament (OPLL) diagnosed on radiographs 4, 2
- Pre-operative surgical planning requiring detailed bony anatomy 2
In all these cases, CT is being used for bony assessment, not for evaluating nerve impingement itself. 2