How do you diagnose a cerebrospinal fluid (CSF) leak in low pressure hydrocephalus?

Diagnosing CSF Leaks in Low Pressure Hydrocephalus

The most effective approach to locate a CSF leak in low pressure hydrocephalus is to begin with high-resolution CT (HRCT) of the skull base, followed by MRI brain with contrast, and then proceed to specialized studies like CT cisternography or digital subtraction myelography if needed. 1

Initial Imaging Approach

Step 1: High-Resolution CT (HRCT)

• HRCT of the skull base is the first-line imaging study with 92% sensitivity for detecting CSF leaks 1, 2
• Focus on:
  • Sinonasal region for rhinorrhea
  • Temporal bone for otorrhea
  • Bony defects in the skull base
• HRCT alone is sufficient if only one osseous defect is identified and corresponds with clinical symptoms 1
• No additional preoperative imaging is necessary when a single skull base defect is identified 1

Step 2: MRI Brain with Contrast

• MRI head without and with IV contrast should be performed if HRCT is inconclusive 1, 2
• Look for characteristic findings of intracranial hypotension:
  • Pachymeningeal enhancement
  • Venous sinus engorgement
  • Brain sagging/descent
  • Subdural fluid collections/hygromas
  • Pituitary enlargement with convex superior surface 1, 2

Advanced Imaging for Leak Localization

When Initial Imaging Is Inconclusive:

CT Cisternography

• Indicated when multiple potential CSF leak sites are identified on HRCT 1
• Involves intrathecal administration of iodinated contrast
• Useful for active leaks but less sensitive for slow or intermittent leaks 1

MR Cisternography

• Second-line noninvasive option with 87% sensitivity 1
• Particularly useful when meningoencephalocele is suspected
• Uses high-resolution T2-weighted or steady-state free precession sequences 1

Radionuclide (DTPA) Cisternography

• Reserved for cases where sufficient fluid cannot be collected for β2-transferrin testing 1
• Sensitivity ranges from 76% to 100% for confirming the presence of a leak 1
• Involves intrathecal administration of radiotracer (DTPA labeled with indium-111) 1
• Limited for accurate localization due to pledget movement in nasal cavity 1

Digital Subtraction Myelography

• Highly sensitive for detecting subtle or intermittent leaks 1, 2
• Particularly useful for detecting CSF-venous fistulas
• Involves continuous real-time fluoroscopic imaging of the spine 1

Special Considerations for Low Pressure Hydrocephalus

• In low pressure hydrocephalus with CSF leaks, there is often a blocked communication between the ventricles and subarachnoid space 3
• The leak creates artificially lowered pressure in the subarachnoid space 3
• Complete spine MRI with fluid-sensitive sequences should be performed to evaluate for spinal sources of CSF leak 2
• 3D isotropic heavily T2-weighted sequences provide high spatial resolution for detecting subtle leaks 1

Important Caveats

• Normal initial brain MRI does not exclude CSF leak (approximately 20% may be normal) 2
• Negative initial spine imaging does not exclude CSF leak (46-67% may be normal) 2
• Laboratory confirmation with β2-transferrin or β2-trace protein testing of fluid sample is standard for confirming CSF leak 2
• No radionuclide cisternography or CT cisternography study typically produces positive results without previous visualization of a defect on HRCT 4

By following this systematic imaging approach, the source of CSF leak in low pressure hydrocephalus can be accurately identified, allowing for appropriate targeted treatment to address both the leak and the hydrocephalus.