Intracranial Hypotension/Low Cerebrospinal Fluid Pressure Headache

The low CSF pressure or volume may relate to hypovolemia, overshunting of CSF, or a CSF leak. When the patient is upright, there is traction on the anchoring pain-sensitive structures of the brain, with brain descent or “sagging” in its cranial vault. Symptoms localizing to the cranial nerves and brainstem are thought to be due to traction or compression of these structures, although the hearing changes may relate to alteration of pressure in the perilymphatic system of the inner ear. CSF leaks may occur after any trauma to the meninges, including a lumbar puncture, an epidural injection, or spinal surgery. They may also occur spontaneously through weak meningeal diverticula or weak dura, as can be seen in connective tissue disorders. When the CSF leak is identified, it is most often at the level of the spinal cord, but rarely, intracranial leaks may occur through defects in the cribriform plate or sinuses. These patients may have clear nasal drainage, indicative of CSF rhinorrhea.

Patients with an orthostatic headache should be evaluated with a magnetic resonance image (MRI) of the brain with contrast, looking for diffuse pachymeningeal enhancement, descent of the cerebellar tonsils (mimicking a Chiari I malformation), crowding of the posterior fossa, decreased ventricle size, descent of the optic chiasm, reduction of the prepontine space, pituitary enlargement, engorgement of cerebral venous sinuses, and subdural fluid collections. A normal MRI brain does not rule out low CSF pressure headache and may be normal in up to one third of cases. If the clinical history is suggestive, other testing may be useful to identify the presence of a CSF leak. A radioisotope cisternogram involves injecting a radionuclide into the CSF and monitoring how fast it ascends and diffuses around the brain. A CSF leak can be demonstrated directly by radiotracer accumulation in the extra-arachnoid space or indirectly by a delay in radiotracer ascent to the cerebral convexities. If CSF rhinorrhea is suspected, nasal pledgets are placed with the cisternogram to determine if there is radioactivity in the nasal secretions. Beta-2 transferrin, which is present in CSF, may be detected in CSF rhinorrhea. Lumbar puncture may not be necessary for the diagnosis of low-pressure headache. When performed, this may show a normal-to-low (<60 mm H₂O) opening pressure and normal-to-high CSF protein. Mild pleocytosis (WBC 10-50) may also occur.

Most headaches due to low CSF pressure are self-limited. Conservative measures, such as bed rest, caffeine, and increased fluid intake, are advocated as first-line treatments. A persistent headache may require an epidural blood patch. If the site of the leak is known, the blood patch can be relatively targeted toward this site. In spontaneous CSF leaks, MRI of the spine might show fluid collections outside the arachnoid space, engorgement of the epidural venous plexus, or meningeal diverticula. The presence of a meningeal diverticulum does not, of course, guarantee that it is the site of CSF leak. The most reliable method for detecting the actual site of the leak is to identify extravasation of CSF into the paraspinal soft tissues, which is best seen on a computed tomography (CT) myelogram. When more conservative measures fail, surgical intervention may be considered.

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