Spontaneous intracranial hypotension.

ABSTRACT: Spontaneous intracranial hypotension (SIH) is an increasingly recognized syndrome. Postural headache with typical findings on magnetic resonance imaging (MRI) are the key to diagnosis. Delay in diagnosing this condition may subject patients to unnecessary procedures and prolong morbidity. We describe a patient with Sill and outline the important clinical and radiographic features of this syndrome. Headache due to SIH is similar to headache occurring after lumbar puncture. Patients with postural headaches should have brain MRI before lumbar puncture. Meningeal abnormalities with typical clinical features are helpful in establishing the diagnosis. When correctly diagnosed, SIR management, in most cases, is easy and highly effective.

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SPONTANEOUS or idiopathic intracranial hypotension is rare. Careful history taking and a high level of suspicion are essential to diagnosing this syndrome. Imaging studies, especially MRI, are helpful in confirming the diagnosis and ruling out any other conditions. This condition is usually treatable with simple measures, though failure to recognize it may subject the patient to unnecessary procedures, workup, and treatments. To familiarize physicians with SIH, we present the following case.

CASE REPORT

A 44-year-old right-handed, previously healthy woman went to her primary care physician after having daily headaches for 2 weeks. There was no history of headaches or precursors of migraine. The acute onset of severe headache occurred initially while the patient was working at her office job. The headache began as a pain over the vertex of the head and rapidly became holocephalic. Pain began abruptly and peaked within 15 minutes, She described no aura, visual change, or neurologic symptoms. She described nausea but did not vomit. She definitely described the headache as being relieved by assuming a recumbent position for a few minutes, only to return 15 minutes after assuming an upright position. There was no history of skin rash, tick bites, head trauma, or fever, and family history was negative for headaches. Workup, including computed tomography (CT) of the brain done for evidence of bleeding, was unremarkable. Initial treatment with a nonsteroidal anti-inflammatory drug (NSAID) resulted in minimal improve ment. Three days later, the patient went to her local emergency room because of severe headache worsened by sitting or standing, as well as nausea, anorexia, and decreased fluid intake. Physical examination revealed an ill-appearing woman with mild nuchal rigidity. Blood pressure was normal without orthostasis, and she was afebrile. General medical examination was within normal limits. Neurologic examination revealed normal cranial nerves without papilledema, and her vision was intact. Strength, sensations, and coordination were normal. There was minimal hyperreflexia, though plantar responses were flexor bilaterally. No other pathologic reflexes were elicited. Serum chemistry values, peripheral blood count and differential count, and the erythrocyte sedimentation rate were normal. Magnetic resonance imaging of the brain with gadolinium showed cerebellar tonsillar descent suggestive of Chiari type I malformation and diffuse meningeal enhancement (Fig 1). Lumbar puncture showed an opening pressure of 60 mm. H2 0, with cerebrospinal fluid (CSF) that was clear but drained slowly. Laboratory analysis showed a cell count of 4/mm3 (normal, 0 to 4/mm3), all lymphocytes, no red blood cells, protein value of 45 mg/dL (normal, 30 to 45 mg/dL), and glucose value of 57 mg/dL (normal, 45 to 60 mg/dL). Results of cultures and cytologic examination were negative. Findings on radionuclide cisternography with technetium-labeled diethylenetriamine-pentaacetic acid were normal with no evidence of GSF leak. The patient was admitted, placed on complete bed rest, and given high flow-rate intravenous normal saline and intravenous caffeine sodium benzoate. Her condition improved over the course of 3 days, and she was discharged home. Improvement continued with several additional days of bed rest, increased fluid, and caffeine intake, and symptoms did not recur. Repeated MRI 1 month after discharge showed cerebellar tonsillar ascent and complete resolution of abnormal meningeal enhancement (Fig 2). At 9-month follow-up, the patient report ed no headache or systemic symptoms.

DISCUSSION

The clinical syndrome of SIH shares many similarities to the post-lumbar puncture headache that most physicians are familiar with. (1-7) As the name implies, it occurs in the absence of lumbar puncture or central nervous system (CNS) trauma and may be related to the spontaneous dural tears. (1,2) The International Headache Society (8) recognizes the absence of a definitive pain description for the headache associated with the SIH. In its criteria of 1998, the International Headache Society (8) published the following classification of low CSF pressure (7.2), which includes CSF fistula headache: "Posttraumatic, postoperative or idiopathic fluid leak demonstrated by measurement of glucose concentration in leaking fluid, or by leakage of spinally injected dye or radioactive tracer" with characteristics of post-lumbar puncture headache (Table).

According to Khurana, (1) Schaltenbrand first described this syndrome in 1938 using the term "spontaneous or essential aliquorrhea," emphasizing that it occurs spontaneously, and his terminology implies he attributed the symptoms to the absence of CSF in these patients. Later, the term "hypoliquorrhea" was used. (1) Spontaneous intracranial hypotension is rare, with a prevalence of approximately 1:50,000 persons, and it is more common in women, with female-male ratio of 3:1. (9) Patients with connective tissue diseases or Chiari malformation may be more susceptible to SIH syndrome. (1-5) Postural headache is the cardinal feature of the syndrome and should alert the treating physician to the diagnosis. (1-4) Typically, patients have a sudden onset of headache that is characteristically relieved by lying flat for a few minutes and recurs with resuming an upright position. (2-5) Other conditions that may cause positional headaches (eg, colloid cyst of the third ventricle, rare cases of migraine headaches) are re adily ruled out by MRI findings. (1) The headache in patients with SIH is usually holocranial, though it might be localized to the frontal or occipital head regions. (4) Patients may have additional symptoms, including double vision due to sixth cranial nerve palsy, photophobia, nausea, vomiting, hearing changes, taste changes, malaise, and mental confusion. (2, 4, 5) The mechanism of headache is unclear, but pain could be related to stretching pain-sensitive structures in the cranial vault when the patient is upright because of decreased support by the CSF, which normally keeps the brain floating. (3)

Confirming the diagnosis of low intracranial hypotension syndrome requires imaging studies and CSF pressure measurements, in addition to clinical history. (1, 4) Magnetic resonance imaging with gadolinium is critical in diagnosing this syndrome and to rule out any other underlying conditions and should be obtained as soon as the syndrome is suspected and before measuring CSF pressure. (10-12)

Gadolinium MRI typically shows diffuse non-nodular pachymeningeal enhancement. (10-12) The mechanism behind pachymeningeal enhancement is related to volume depletion. Decreased CSF volume causes a compensatory increase in blood volume. This is reflected mainly in the venous system and the meningeal veins. (13) There is enhancement of the pachymeninges because they have no blood-brain barrier, contrary to the leptomeninges, which have an intact blood-brain barrier and no enhancement. (14, 15) Diffuse MRI meningeal enhancement can be seen in other conditions, including meningitis, encephalitis, neurosarcoidosis, and meningeal carcinomatosis. (16) Other findings on MRI include occasionally seen subdural fluid collection and descent of the brain. (2, 11) In some patients with SIH, chronic CSF drainage results in sagging and hemiation of the cerebellum and medulla through the foramen magnum simulating Chiari I malformation (similar to our patient's condition). However, other findings on MRI (diffuse meningeal enha ncement) readily differentiate patients with SIH and torisillar descent from patients with idiopathic Chiari I malformation. Abnormalities seen on MRI (meningeal enhancement and tonsillar descent) clear or improve substantially with clinical improvement of the headache. (10, 11) In patients with persistent symptoms, spinal MRI, radioisotope cisternography, and computed tomographic myelography can be used to identify the site(s) of CSF leakage, (9, 17) though as in our patient radioisotope cisternography may not show any abnormalities. Nasal packing should be done when radioisotope cisternography is used to rule out CSF leakage through the cribriform plate. (1, 5)

Carefully performed lumbar puncture is critical in confirming the diagnosis and in ruling out any underlying cause for the meningeal enhancement. (1, 4) If STH is clinically suspected, MRI should be done before obtaining the lumbar puncture, since lumbar puncture by itself may cause meningeal enhancement. (10-12) In many cases, there will be no spontaneous CSF drainage if CSF pressure is <60 mm [H.sub.2]O. (11) Results of CSF studies are normal otherwise, with occasional mild lymphocytic pleocytosis and an elevated protein value, (5) a finding that may be related to local disruption of the blood-brain barrier. (3-5)

Recently, a few cases of intracranial hypotension without headache have been described. (14) These cases were seen in few elderly patients after CSF shunt procedure and were diagnosed by typical MIRI findings and CSF opening pressure, without evidence of CNS infection or inflammation. (14)

Failure to recognize Sill may subject patients to unnecessary procedures. In many reports, patients with this syndrome have had unnecessary procedures such as repeated lumbar punctures (to rule out infection), meningeal biopsy, and multiple courses of drug therapy before the correct diagnosis was discovered. (4, 5) Once the diagnosis of SIH is established, measures to increase CSF production and increase intracranial pressure should be used to improve the headache. (3,5) Similar treatment approaches are used in patients with headache after lumbar puncture. (3) Most patients improve spontaneously or with conservative symptomatic therapy with bed rest and increased fluid intake. (1-3) Caffeine given orally (18) or intravenously (19) is reported to be effective in 75% to 85% of patients with post-lumbar puncture headache. Caffeine is frequently used as first-line therapy in patients with SIH. (16-18) The mechanism by which caffeine increases CSF production is unclear. Caffeine is an adenosine receptor antagonist that decreases cerebral blood flow and secondarily increases CSF production. (19) Theophylline is another adenosine receptor blocker that has been used with some success. (20) Analgesics are usually not effective in treating low-pressure headaches. (1-3) In one study, sumatriptan was found to be ineffective in patients with low-pressure headaches, after failure of conservative management. (21) Steroids have been empirically used, with variable results. (3-5,15) In a minority of patients, symptoms persist and necessitate more aggressive therapy. (3) Epidural autologous blood patch is effective in relieving low intracranial pressure headaches, (22-24) though previous estimates of epidural blood patch efficacy were overgenerous. Persistent symptomatic relief can be expected in 61% to 75% of patients. (22) In some cases, treatment has been effective even after many months of the onset of headaches. (23) Radio-logic improvement in addition to clinical improvement after epidural blood patch has been reported. (24) Complications due to epidural blood patch include infection, chemical inflammation, paresthesias in the lower limbs, neck stiffness, and radicular pain. (25,26) Another treatment method is continuous epidural saline infusion. (27) Although initially effective, epidural saline infusion is associated with a high incidence of headache recurrence. (22) The majority of patients with SIH respond to conservative and medical therapy, but a few will require a more aggressive diagnostic and therapeutic approach. Using spinal MRI, computed tomographic myelography, and radioisotope cisternography may help determine the site(s) of CSF leak. Intraoperative intradural exploration with saline or dye injection intradurally has been used to identify accessible CSF leakage sites, which can be at any part of the spinal cord. (1,5,9) Surgical repair of the leak is rarely used and only if medical therapy fails and there is a clear and accessible source of the CSF leak. (5,9)

In summary, SIH is a unique medical syndrome with characteristic clinical history and findings on imaging studies. Failure to recognize this syndrome may subject the patient to unnecessary medical treatments and procedures. When diagnosed, excellent outcome can be achieved by symptomatic therapy in most patients.

TABLE. Diagnostic Criteria for Headache After Lumbar Puncture *

Bilateral headache developed less than 7 days after lumbar puncture.
Headache occurs or worsens less than 15 minutes after assuming the
 upright position, and disappears or improves less than 30 minutes
 after resuming the recumbent position.
Headache disappears within 14 days after lumbar puncture.


* 7.2.1 Post-lumbar puncture headache.

From the Headache Classification committee of the International
Headache Society. (8)

References

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(18.) Camann WR, Murray RS, Mushlin PS, et al: Effects of oral caffeine on postdural puncture headache. a double-blind, placebo-controlled trial. Anesth Analg 1990; 70:1181-1184

(19.) Chio A, Laurito CE, Cunningham FE: Pharmacological management of postdural puncture headache. Ann Pharmacother 1996; 30:831-839

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RELATED ARTICLE: KEY POINTS

* Spontaneous intracranial hypotension is characterized by postural headache that worsens when patients sit or stand and then diminishes on recumbency.

* When the diagnosis is suspected, magnetic resonance imaging of the brain should be obtained before attempting a lumbar puncture.

* Most patients respond well to supportive therapy with increasing fluid intake, bed rest, and oral or intravenous caffeine intake.

* Epidural blood patch and rarely surgical intervention may be used in refractory cases.

From the Department of Neurology, University of North Carolina at Chapel Hill.

Reprint requests to Megdad Zaatreh, MD, Yale University, Department of Neurology, PO Box 208018, New Haven, CT 06520-8018.