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

Screening for CSF Leak in Low Pressure Hydrocephalus

MRI of the brain with intravenous contrast and MRI of the whole spine should be performed as first-line investigations for screening CSF leaks in low pressure hydrocephalus. 1

Initial Diagnostic Approach

First-Line Imaging

1. Brain MRI with IV contrast

   • Essential to identify imaging signs of intracranial hypotension 1
   • Look for:
     • Pachymeningeal enhancement
     • Brain sagging
     • Venous engorgement
     • Subdural collections
     • Pituitary enlargement
     • Tonsillar descent

2. Whole spine MRI

   • Should include:
     • Fat-suppressed T2-weighted sequences (STIR)
     • T2-weighted sagittal images (3-4mm thickness)
     • T2-weighted axial images (3-4mm thickness)
     • High-resolution heavily T2-weighted 3D sequences (CISS, FIESTA, bFFE, SPACE) 1
   • Helps identify:
     • Epidural fluid collections
     • Meningeal diverticula
     • CSF-venous fistulas

Laboratory Testing

• Beta-2 transferrin testing of fluid samples is the gold standard laboratory test for confirming CSF leak 2

Advanced Imaging When Initial Studies Are Negative

If initial MRI studies are negative but clinical suspicion remains high:

1. CT Myelography

   • Dynamic CT myelography plays an important role in subsequent imaging workup 1
   • Positioning depends on suspected leak location:
     • Prone positioning for ventral dural defects
     • Decubitus positioning for suspected meningeal diverticulum or CSF-venous fistula 1

2. Digital Subtraction Myelography

   • Particularly useful for detecting CSF-venous fistulas 1
   • Involves continuous real-time fluoroscopic imaging
   • May require two separate contrast injections when performed in decubitus position 1

3. DTPA Cisternography

   • Can detect CSF leaks with similar accuracy to conventional CT myelography 1
   • Limited by lower spatial resolution
   • Sensitivity ranges from 76-100% 1

Special Considerations for Low Pressure Hydrocephalus

In low pressure hydrocephalus specifically:

• CSF leaks may be the cause of negative-pressure or low-pressure hydrocephalus, especially after cranial base approaches 3
• These cases present with symptoms of high intracranial pressure and ventriculomegaly despite measured low or negative pressures 3
• A blocked communication between the ventricles and subarachnoid space is often present 3

Management Algorithm

1. Initial screening:

   • Brain MRI with contrast + whole spine MRI
   • If positive: Proceed to targeted treatment
   • If negative: Continue to step 2

2. Secondary screening (if high clinical suspicion remains):

   • Review imaging with neuroradiologist
   • Consider differential diagnoses
   • Refer to specialist center for multidisciplinary team discussion 1

3. Tertiary screening:

   • Dynamic CT myelography or digital subtraction myelography
   • Consider decubitus positioning for suspected CSF-venous fistula 1

Pitfalls and Caveats

• Normal brain and spine MRI does not rule out CSF leak - approximately 20% of initial brain MRIs and 46-67% of initial spine imaging may be normal in patients with clinically suspected spontaneous intracranial hypotension 1
• CSF pressure can be normal in patients with spontaneous intracranial hypotension 1
• Lumbar puncture should not routinely be performed solely to confirm diagnosis of spontaneous intracranial hypotension 1
• CSF-venous fistulas and slow meningeal diverticular leaks are often subtle findings that may require advanced imaging techniques 1
• In low pressure hydrocephalus specifically, the CSF leak creates artificially lowered pressure in the subarachnoid space, requiring subatmospheric external ventricular drainage for treatment 3