Clinical Pearls & Morning Reports
Spontaneous intracranial hypotension is a condition characterized by a lower-than-normal volume of cerebrospinal fluid (CSF) because of leakage of CSF through the dural membrane at one or multiple sites. The loss of CSF results in displacement of cerebral structures, causing headache and other neurologic symptoms. Read the NEJM Review Article here.
Q: What are some of the causes of spontaneous intracranial hypotension?
A: A CSF leak within the spinal column is the most common identifiable cause of spontaneous intracranial hypotension. Imaging of the spine and intraoperative observations have identified three types of spontaneous spinal CSF leaks. One type is due to a linear tear in the dura located ventral to or posterolateral to the spinal cord. A second type is associated with leakage at sites of simple meningeal diverticula (Tarlov cysts) or with diffuse dilatations of the dural sac, as occurs in ankylosing spondylitis. The third type, which is still being characterized, has been attributed to a spinal CSF–venous fistula. An underlying connective-tissue disorder may facilitate a rent in the dura that results in spontaneous intracranial hypotension, but with the exception of Marfan’s and Ehlers–Danlos syndromes, such disorders are rarely identified. Spinal osteophytes or calcified disk herniation may abrade or penetrate the dura, causing a dural tear, and typically result in ventral spinal leaks.
Q: Describe features of the headache associated with spontaneous intracranial hypotension.
A: The cardinal symptom of spontaneous intracranial hypotension is a headache that worsens on standing and subsides with lying down (orthostatic headache). A few patients have a nonpositional or even reverse orthostatic headache (worse when the patient is recumbent). The headache is usually holocephalic or bilaterally suboccipital but may be unilateral and occasionally has a throbbing component that simulates migraine.
A: The diagnostic criteria for spontaneous intracranial hypotension in the International Classification of Headache Disorders, third edition, include evidence of typical findings on magnetic resonance imaging (MRI) of the head, CSF leak on spinal imaging, or low CSF pressure as measured by lumbar puncture. Gadolinium-enhanced MRI is most often used and typically shows enhancement of the pachymeninges (dura), as well as features of subdural fluid collections, engorgement of venous structures, pituitary enlargement, sagging of the brain, or reduction in the volume of the optic-nerve sheath subarachnoid space. Pachymeningeal enhancement is the most common and recognizable feature on imaging and has been attributed to secondary dilatation of the venous system in the cranial dura as a result of the lowered volume of CSF within the intracranial space (the Monro-Kellie doctrine). The site of spinal CSF leakage can be determined in most patients but depends on the thoroughness of the investigation. Low CSF pressure, or pressure at the low end of the normal range, is not necessary for a diagnosis of spontaneous intracranial hypotension, since patients may have normal or even elevated CSF pressure.
A: Depending on the severity of the symptoms, a practical approach includes a short course of conservative measures over a period of a few days or weeks, consisting of bed rest, high oral fluid intake, caffeine, and an abdominal binder. The main therapeutic maneuver in patients whose condition is not improved with conservative measures is an epidural “blood patch,” whereby autologous blood obtained by venipuncture is injected into the lumbar spinal epidural space. It is not necessary to identify the site of the CSF leak in order to achieve good results with a blood patch in the lumbar spine. For patients with persistent symptoms after blood patching, specialized spinal imaging with digital-subtraction myelography or dynamic CT myelography may be necessary to localize the site of the CSF leak. This allows for treatment with directed epidural blood patching or glue injections to seal the site of the CSF leak or for microsurgical repair of the leak.