Can a CT (Computed Tomography) myelogram be used to identify a cerebrospinal fluid (CSF) leak?

CT Myelography for CSF Leak Detection

CT myelography is an effective diagnostic tool for identifying cerebrospinal fluid (CSF) leaks, playing an important role in the subsequent imaging workup of spontaneous intracranial hypotension (SIH) after initial brain and spine imaging. 1

Role of CT Myelography in CSF Leak Detection

CT myelography serves as a valuable technique in the diagnostic algorithm for CSF leaks, particularly when initial imaging is inconclusive. The American College of Radiology recommends a stepwise approach:

1. Initial imaging: Brain MRI with and without contrast, followed by complete spine MRI with fluid-sensitive sequences 2
2. Secondary imaging: CT myelography when initial imaging is inconclusive or to better characterize leak location 1

Types of CT Myelographic Techniques

Conventional CT Myelography

• Involves intrathecal injection of contrast followed by CT scanning
• Can detect epidural contrast collections suggestive of dural defects or leaking meningeal diverticula 1
• Provides useful information on how subsequent dynamic studies should be performed 1

Dynamic CT Myelography

• More advanced technique for detecting subtle or high-flow leaks
• Involves an initial scan followed by delayed phase scans in immediate succession 1
• Particularly valuable when other examinations are unsuccessful 3
• Can precisely localize fast CSF leaks that might be missed by conventional techniques 4
• Different positioning options:
  • Prone positioning: Successful for most ventral leaks 4
  • Lateral decubitus positioning: Valuable when prone studies are unrevealing, especially with dorsal/lateral epidural fluid collections 4

Advantages of CT Myelography

• High spatial resolution for precise leak localization
• Can detect various types of leaks:
  • Dural tears
  • CSF-venous fistulas
  • Leaking meningeal diverticula 1, 3
• Newer technologies like photon-counting detector CT myelography show promise for detecting previously occult CSF-venous fistulas 5

Limitations and Considerations

• Requires lumbar puncture for contrast administration
• Involves radiation exposure (mean dose-length product of 1347 mGy·cm in one study) 3
• Iopamidol is commonly used as contrast with specific dosing guidelines:
  • Adults: 2000-3000 mg iodine (10-15 mL of 200 mgI/mL solution for myelography)
  • Formulations >300 mgI/mL should not be used intrathecally in adults 6
• Patients should be well-hydrated before and after the procedure 6

Special Techniques for Challenging Cases

• For high-flow leaks, dynamic CT myelography provides high temporal and spatial resolution 7
• For cryptogenic leaks (where previous imaging didn't show the dural breach), modified dynamic CT myelographic techniques can locate the precise leak point 3
• For post-operative paraspinal fluid collections, direct pseudomeningocele contrast injection can be considered as an alternative to conventional CT myelography 8

Best Practices for CT Myelography

• Inject contrast slowly (over 1-2 minutes) to avoid excessive mixing with CSF 6
• Maintain patient's head elevated above highest level of spine during positioning 6
• Allow at least 48 hours (preferably 5-7 days) between repeat examinations 6
• Post-procedure, maintain patient in head-up position for 24 hours 6

CT myelography remains a crucial diagnostic tool in the workup of suspected CSF leaks, particularly when initial MRI findings are inconclusive or when precise localization is needed for targeted treatment.