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Spontaneous Intracranial Hypotension
Introduction
The intracranial pressure is controlled by the production, flow, and absorption of the cerebrospinal fluid. If there is an alteration in these processes leading to an alteration in the CSF pressure, there is a manifestation of neurologic symptoms that is most commonly a headache. Spontaneous intracranial hypotension (SIH) presents with postural headache and low cerebrospinal fluid (CSF). The underlying cause is usually a CSF leak.[1]
In the majority of the cases, brain magnetic resonance imaging (MRI) will show diffuse meningeal enhancement. However, a few cases have been reported in which the patient had a non-orthostatic headache, normal CSF pressure, and no meningeal involvement on MRI. Historically, different terms have been used to describe this process, such as spontaneous or idiopathic low CSF pressure headache, liquorrhea, low CSF volume headache, CSF hypovolemia, CSF volume depletion, hypoliquorrhoeic headache, and CSF leak headache.[2]
Etiology
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Etiology
A CSF leak can be congenital or traumatic due to dural defects. These defects are usually present in the form of fistulas or tears, which result in CSF leaks. Spontaneous intracranial hypotension is actually due to a decrease in volume of the CSF instead of the old notion that SIH is due to a barometric drop in CSF pressure.[3] There are various factors that can lead to leakage of CSF, like the absence of dura around the nerve root sheaths, congenital connective tissue disorders causing structural abnormalities, osteophyte protrusions, and the herniation of the spinal disc. Focal weakness in the dura can be found around the thoracic and lumbar spine. These arachnoid diverticula are especially prone to CSF leaks.[4][5][6] Trauma, surgery, and over drainage of the CSF shunt can also cause spontaneous intracranial hypotension.[7]
Epidemiology
The incidence of spontaneous intracranial hypotension is around 5 in 100,000. The ratio between females and males is 2:1, indicating that it is more common in females. Even though children and old adults are affected by SIH, the peak incidence of SIH is around 40 years.[8]
Pathophysiology
The leakage of CSF from the craniospinal vault is thought to be the cause of spontaneous intracranial hypotension. Normally, the weight of the brain is nearly 1500 grams in air. This weight is decreased to about 48 grams in a pool of CSF due to the buoyancy provided by the fluid.[9] When CSF volume decreases due to leaking or other causes, it precipitates the sagging of the brain in the cranial vault. This sagging causes traction on the sensory nerves of the meninges and the bridging veins, leading to headaches.[10] Postural headache is due to the fact that the traction on the meninges is increased in an upright position leading to increased intensity of headache when standing. Low CSF pressure in the cranial vault is compensated by an increase in vasodilation of the cerebral vessels. This phenomenon causes headaches due to increased brain volume.[11]
Another hypothesis for the underlying mechanism of precipitation of headache in spontaneous intracranial hypotension is that there is an increase in compliance at the lower end of CSF spinal space whenever there is a spinal CSF leak. The lack of equilibrium in the craniospinal elasticity precipitates orthostatic headaches. Other supporting evidence for this hypothesis is the fact that orthostatic headaches are more common with spinal CSF leakage as compared to cranial CSF leakage (e.g., with CSF otorrhea or CSF rhinorrhea).[12]
Connective tissue disorder can also be the underlying cause of the development of spontaneous CSF leaks. The connective tissue abnormality, which includes abnormalities of fibrillin or elastin, can cause dural weakness, which eventually plays a role in causing spontaneous low CSF pressure due to cryptic CSF leaks.[13] Meningeal diverticula are often a finding in patients with Marfan syndrome. They are implicated in the development of CSF leaks, thus making connective tissue disorders an associated disease.[14][15]
There are different events that can incite a rupture of spinal epidural cysts, a tear of the dural nerve sheath, or the rupture of perineural cysts.[16] These events can be as benign as a sudden sneeze, sports activity, a twist, fall, orgasm, sexual intercourse, or some other type of benign trauma.
In rare cases, a CSF venous fistula can develop between the subarachnoid space and their adjacent spinal epidural veins. There is direct drainage of CSF from subarachnoid space into spinal epidural veins without the formation of any dural defect.[17]
History and Physical
Patients with spontaneous intracranial hypotension usually present with postural headaches.[16] However, in some cases, there are other neurological symptoms that are more pronounced. These include nausea, neck pain, vomiting, neck stiffness, anorexia, diaphoresis, diplopia, photophobia, hiccups, unsteady gait, hyperacusis, tinnitus, blurred vision, and dysgeusia, etc.[8][18][19]
The headache associated with spontaneous intracranial hypotension can be sudden or gradual in onset, generalized or focal, and often a throbbing or dull type of headache. The severity of the headache is also variable ranging from mild to incapacitating.[8][20] The headache is relieved within minutes of lying down. In cases with asymmetric CSF leak, only lying on one side will result in the resolution of the headache.[21] The headache can be exacerbated by sneezing, coughing, erect posture, movement of the head, and high altitude.[22]
Evaluation
Brain and spinal MRI should be included in the initial workup if spontaneous intracranial hypotension is suspected. CSF pressure measurement can also provide a major hint. The temporal relation of postural headache with trauma or surgery also points to the diagnosis of spontaneous intracranial hypotension. Brain MRI, both with and without contrast, is useful. The presence of dispersed uniform pachymeningeal enhancement is diagnostic in most cases.[23] Other common findings on imaging include subdural hematoma and hygromas, engorgement of venous sinuses, contracting size of the cisterns and ventricles, increased diameter of the brainstem, and pituitary enlargement, etc.[24] The appearance of “sagging” of the brain along with the herniation of cerebellar tonsils is also common. This is also accompanied by the sinking of the brainstem, which can make it look like Arnold Chiari 1 malformation.[25]
A retrospective study of 165 patients with spontaneous intracranial hypotension showed that 31 had a subdural hematoma, and 103 had imaging findings of pachymeningeal enhancement on MRI. Brain MRI, CT myelography, and MR myelography can help in localizing the CSF leaks in the patients. MRI localized the leaks in 152 of 165 patients, MR myelography localized the leaks in 111 of 117 patients, and CT myelography was able to identify CSF leaks in 43 of 48 patients with spontaneous intracranial hypotension. Moreover, 149 of 165 patients had CSF leaks at multiple levels, with the majority (63.9 %) present in the cervicothoracic region.[26]
Spinal MRI can play a big role in spotting the point where CSF leakage is occurring. Moreover, it can help in establishing the diagnosis. The findings on spine MRI might include the epidural leakage of the fluid, presence of meningeal diverticula, fluid collection in the extra-meningeal cavity, and the shrinking of the dural sac in addition to distended epidural venous plexus.[27]
The diagnostic criteria for spontaneous intracranial hypotension in the International Classification of Headache Disorders (3rd Edition) include the following points:[28]
1) Headache that can fulfill criterion number 3
2) Presence of low CSF pressure
3) A chronological relation of headache with CSF leakage or low CSF pressure
4) Findings are not explained by any other disease or phenomenon
Treatment / Management
The choice of treatment of spontaneous intracranial hypotension depends on the severity of the symptoms. If the headaches are acute and uncomplicated with severity ranging from mild to moderate, conservative management is advised.[29] The strategies involved in conservative treatment aim to curtail the CSF leak. Strict bed rest, plenty of caffeine intake, avoiding sitting upright, and the addition of analgesics are included in conservative management. High intake of salt, oral, or IV hydration help in restoring the volume of the CSF, which in turn alleviates the symptoms.[11](B3)
If the symptoms persist even after 1 to 2 weeks of conservative management or the headache is associated with debilitating features, the first-line therapy would be an epidural blood patch (EBP). EBP is also indicated in patients with a connective tissue disorder, an aggressive method of injury leading to the symptoms, or when the symptoms are present for more than 2 weeks at the point of diagnosis.[30][31] (B3)
The hypothesis proposed for EBP effectiveness is that it can produce a tamponade of the CSF leak causing the resolution of the symptoms in the short term. Also, in the long term, it causes deposition of fibrin and the formation of scar tissue around the leaks providing long-term management.[11](B3)
Epidural fibrin glue and surgical correction of the leaks are the next treatment options if the patient is not managed effectively even after repeated epidural blood patch trials. Epidural fibrin glue is effective in nearly one-third of the patients who were not managed with EBP trials. Moreover, it is a good alternative treatment in comparison to surgical correction of the CSF leaks. However, both epidural fibrin glue seal and surgical correction of the CSF leaks require the identification of the points where CSF leak is occurring.[8][32](B3)
The failure of nonsurgical therapies warrants the surgical correction of the CSF leaks.[7] This requires the identification of the point of CSF leaks with CT myelography or MR myelography. The meningeal diverticular leaks are ligated with sutures or metallic clips.[8] Sutures, in addition to the use of fibrin glue, placement of muscle pledget, or gel foam, can help in managing the dural defects and tears.[33](B3)
Patients who fail adequate treatment with EBP, with no identification of points of CSF leaks, are treated with continuous epidural infusion of dextran or saline. This helps in replenishing the CSF volume, which can, in turn, alleviate the symptoms.[34](B3)
Differential Diagnosis
There are a few conditions that present similarly to spontaneous intracranial hypotension. Postural tachycardia syndrome can present as an orthostatic headache. But in such cases, there is no associated leakage of CSF.[35]
The over drainage of the CSF shunts can also manifest as a clinical picture that is similar to spontaneous intracranial hypotension.[23] Moreover, orthostatic headaches, along with a dry tap, do not always indicate that there is a CSF leak or spontaneous intracranial hypotension. A case was reported in which there were orthostatic headaches that started after a dry tap. However, the MRI revealed a lumbar intradural mass, which was eventually resected. The mass was identified as myxopapillary ependymoma.[36]
Prognosis
In a few cases, there is evidence of the resolution of spontaneous intracranial hypotension in a time frame of 2 weeks.[37] Some patients will continue to suffer from the symptoms even after the resolution of CSF leaks.[38]
In others, the condition can go on for months or even years in rare cases. If intermittent CSF leaks are occurring with intervals of weeks or months, they can produce intermittent headaches with no symptoms in between.
In nearly 10 percent of patients afflicted with spontaneous leakage of the CSF, the condition will reoccur despite the proper treatment.[8]
Complications
During EBP, autologous blood ranging from 10 to 20 cc is infused into the epidural space.[11][39] If the initial trial is unsuccessful, volume ranging from 20 to 100 cc is used. This higher ratio of volume can lead to back pain or radiculopathy. Other adverse effects associated with EBP include fever and leg paresthesias.[8]
A rare complication of spontaneous intracranial hypotension is coma. This is due to the sagging of the brain. Closure of the CSF leak is the solution to regaining consciousness in coma associated with spontaneous intracranial hypotension.[40]
Deterrence and Patient Education
Patients should be educated about the disease. Before performing a lumbar puncture, it is ideal to educate the patient about possible complications, including spontaneous intracranial hypotension. The basis of successful conservative management is dependent on better patient education. Educational handouts and online sources can be recommended to patients to help them better understand the disease. This will eventually result in better compliance with recommendations by healthcare professionals.[8]
Enhancing Healthcare Team Outcomes
Spontaneous intracranial hypotension can cause debilitating symptoms. Moreover, it is crucial for the healthcare provider to keep a high level of clinical suspicion to be able to diagnose the disease timely. The diagnosis, treatment, and management of the patient are dependent on excellent teamwork and coordination between an interprofessional team that includes internists, neurologists, radiologists, and neurosurgeons, etc. Moreover, nurses can play an important role in educating the patient about the disease.[8]
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