Myth 1: SIH Is Defined by Low CSF Pressure
Although SIH is commonly defined as a low opening pressure (<6 cm H2O), normal CSF pressure is a common presentation and should not be overlooked. CSF pressure increases with time, despite the presence of active leaks. Kranz and colleagues suggest that it is CSF volume, rather than pressure, that is the underlying mechanism of SIH, and that the integrity of the relationship between CSF volume and CSF pressure varies with changes from supine to upright posture and with loss or removal of CSF.
Myth 2: SIH Presents Only As an Orthostatic Headache
The classic presentation of SIH is a headache that worsens in an upright position and is often relieved by lying down. It is often accompanied by tinnitus, neck pain, and intrascapular pain. However, Kranz et al found a number of other presentations common to SIH, including "second half of the day" headaches, headaches that evolve into nonpositional headaches, and headaches that disappear while other symptoms of CSF leakage (such as tinnitus and vertigo) persist. Some headaches are even nonorthostatic at origin.
Myth 3: Normal Brain Magnetic Resonance Imaging Scans Exclude SIH
Magnetic resonance imaging (MRI) is an important diagnostic tool for SIH, which is often characterized by the presence of diffuse, smooth enhancement of the dura and may include sagging midbrain, dilated dural venous sinuses, and hyperemia of the pituitary gland, as well as occasional subdural effusions. The absence of all these findings, however, should not rule out a diagnosis of SIH, the authors found, because they were absent in from 17% to 39% of cases studied.2 More important, MRI signs often did not correlate with low CSF pressure. They recommended further CSF pressure measurements if MRI is not supportive in suspected SIH.
Myth 4: Dural Enhancement Suggests a Multipathogen Workup
Dural enhancement is highly specific to SIH; however, those unfamiliar with SIH imaging may consider ordering other tests to rule out infectious, granulomatous, and neoplastic disorders. Kranz and colleagues considered this a common diagnostic error, resulting in needless and often extensive testing of the CSF in search of less likely pathogens. Instead, clinicians should look for 2 cardinal features that are exclusive to a diagnosis of SIH: smooth dural enhancement and diffusion. If both are present, then other pathogens need not be investigated.
Myth 5: Chiari I Is a Feature of SIH
Descent of the midbrain detected on MRI in SIH is often mistaken for Chiari I, a congenital malformation of the brain that does not appear suddenly, as brain sagging in SIH does. It is important to differentiate between these 2 presentations, however, as they are treated differently. Brain sagging in SIH is a direct result of CSF leakage, and a suboccipital craniectomy, the standard treatment to relieve pressure caused by Chiari I, will not stop the CSF leak. Because both conditions may present with cerebellar tonsillar ectopia, the authors recommend examination of the third ventricular floor and mamillopontine distance for signs of sagging, a clear indication of SIH.
Myth 6: Tarlov Cysts Are the Underlying Cause of All CSF Leaks
It is important to identify the source of the CSF leak to target treatment. Although Tarlov cysts may appear similar to normal cervical and thoracic perineurial cysts that are seen on imaging in SIH, they are rarely, if ever, a cause of CSF leakage. Spontaneous dural damage to the meningeal diverticula triggering herniation are a primary cause of CSF leaks, along with ventral dural tears caused by calcified osteophytes and CSF-venous fistula.
Myth 9: The Epidural Blood Patch Immediately Cures SIH
The first line of treatment for CSF leaks is epidural blood patching used to treat postdural puncture headache (PPH). Although response time in PPH is usually immediate, it often takes longer in SIH. This may be related to the lag time between onset of a spontaneous CSF leak and the treatment, as PPH is often diagnosed soon after puncture and the source is known. Because a spontaneous CSF leak can go undetected for some time, the intracranial and paraspinal veins may engage in compensatory mechanisms and CSF production rates may be altered, all of which may continue even after epidural patch treatment. For these reasons, Kranz and colleagues recommend counseling patients with SIH to expect improvement within a week of treatment.
Myth 10: One Treatment for SIH Is All It Takes
The authors reported a high perception among clinicians that a single epidural blood patch treatment is all that is needed to completely resolve SIH. In reality, initial success rates from the patch vary significantly, from 30% to 70%. The procedure often needs to be repeated to achieve remission, and relapse occurs in some patients. In difficult-to-treat cases, such as those with high-flow leaks, surgical intervention may be necessary.
Myth 7: Spinal Images Are Not Likely to Reveal the Source of the CSF Leak
Kranz et al found that between 2 investigations, computed tomography (CT) myelogram or spinal MRI reported the presence of CSF leaks 51% to 55% of the time, although a third study only showed results in 26% of cases. The authors argue that detection rates are high enough to be valuable to supporting a diagnosis of SIH, and especially to targeting treatment considerations (including epidural patching and surgery), by helping to locate the source.
Myth 8: Skull-Based Leaks Are a Cause of SIH
Not all CSF leaks cause SIH. Because leaks to CSF may spontaneously occur in 2 locations (at the base of the skull or along the spine), they produce 2 different clinical syndromes that are mutually exclusive. Those that produce SIH usually occur in the cervical spine, the "zero-pressure point" in the spine where the pressure in the CSF transitions from negative to positive. These points are most likely to leak when standing upright, causing the headache, and to be relieved on lying down.
Leaks occurring at the base of the skull are likely to produce symptoms involving the middle or inner ear and headaches that are not orthostatic. Skull-based CSF leaks were found to have no direct association with SIH, but were directly associated with idiopathic intracranial hypertension. Skull-based imaging, therefore, is not of value in SIH.
Once believed to be rare, spontaneous intracranial hypotension (SIH) is currently estimated to occur at a rate of 5/100,000 individuals. The incidence of SIH, a secondary cause of headache resulting from cerebrospinal fluid (CSF) leaks, has been increasing in recent years as the condition is better recognized in clinical practice. In a 2018 review,1 Kranz et al debunks common myths and misperceptions of SIH that interfere with clearly identifying the condition.
Compiled by Linda Peckel
- Kranz PG, Gray L, Amrhein TJ. Spontaneous intracranial hypotension: 10 myths and misperceptions. Headache 2018;58:948-959.
- Kranz PG, Tanpitukpongse TP, Choudhury KR, et al. Imaging signs in spontaneous intracranial hypotension: Prevalence and relationship to CSF pressure. Am J Neuroradiol. 2016;37:1374-1378.