Author: Danielle Miller, MD (EM Resident Physician, PGY-2, NUEM) // Edited by: Colin McCloskey, MD // Expert Commentary: Brian Sellers, MD
Citation: [Peer-Reviewed, Web Publication] Miller D, McCloskey C (2016, July 19). A Highly Gifted Juice: Opening Pressure In Idiopathic Intracranial Hypertension [NUEM Blog. Expert Commentary by Sellers B]. Retrieved from http://www.nuemblog.com/blog/highly-gifted-juice/
An Evidence Based Approach To Opening Pressure in CSF Analysis and its Role in Idiopathic Intracranial Hypertension
A 27 year-old obese female with a past medical history of migraines presents with the worst headache of her life. A non-contrast head CT shows no mass and no blood. A lumbar puncture (LP) is performed to rule out SAH and to measure opening pressures. The intial opening pressure is 44 with a closing pressure of 21. The CSF is negative for blood. A diagnosis of idiopathic intracranial hypertension (IIH) is suspected.
The History Of The Lumbar Puncture
Cerebrospinal fluid was originally identified by Swedish mystic Emanuel Swedenborg in 1736, who described the fluid as a “spirituous lymph’ and “highly gifted juice.” 
The first LP was performed in the late 19th century by Heinrich Iraneus Quincke and Walter Essex Wynterin. At that time, the mortality rate of the procedure was high as a result of being performed on sick patients and involvinga large incision with a scalpel down to the spinal cord . As early as the 20th century, scientists started to measure opening pressures .
Does positioning matter?
Yes, the patient must be lying in lateral decubitus to essentially zero the manometer. The head should be in line with the right atrium, which should be in line with the spinal needle. Technically, the legs should be extended to minimize falsely elevated values. Opening pressures in the seated position are elevated by approximately 25 cm H20 .
Seriously, leg extension?
Studies suggest that hip flexion may increase CSF opening pressure by increasing intra-abdominal pressure . A study in 1991 found that a flexed position increased opening pressures by 6–8 cm H2O . However, a more recent study in 2001, found differences of only 1–2 cm H2O .
Does BMI affect opening pressures?
Yes, there is a correlation between BMI and opening pressure, but the values are clinically insignificant, with ranges still remaining 10 cm H20 to 25 cm H20 .
What Disease States Should I Worry About With A High Opening Pressure?
Processes that block CSF reabsorption by the arachnoid granulations or increase/obstruct the venous outflow pathway:
Idiopathic intracranial hypertension (IIH)
Cerebral venous sinus thrombosis
Intracranial or spinal mass
Scarring inflammation (sequelae of meningitis, SAH)
Any process that increase venous pressures:
Superior vena cava syndrome
Elevated right heart pressures
Medications (tetracyclines, nitrofurantoin, and nalidixic acid), amiodarone, cyclosporin, systemic and topical steroids, and the oral contraceptive pill 
Do you need a high opening pressure to diagnose IIH?
Yes and no, IIH is diagnosed with the Dandy criteria:
Signs & symptoms of increased intracranial pressure such as headache, visual changes, tinnitus, or papilledema
No other neurologic deficits or evidence of impaired consciousness
Elevated intracranial pressure with normal CSF analysis.
A neuroimaging study that shows no etiology for intracranial hypertension
No other cause of intracranial hypertension apparent 
However, if a patient does not have an elevated opening pressure, the patient can still have IIH, given that intracranial pressure (ICP) fluctuates throughout the day.
Why is opening pressure high in IIH?
The true pathophysiology is unknown. Recent studies have suggested that cerebral venous outflow abnormalities lead to elevated intracranial venous pressures, which leads to increased ICP, and thus higher opening pressures. Causes of outflow abnormalities include venous stenosis or venous hypertension. However, none of the studies can determine if the venous abnormalities are the cause of IIH or merely secondary to the disease process itself .
So will the LP that was just performed in the ED on the patient with suspected IIH really alleviate the patient’s headache?
Maybe. Use of LP in symptom management is controversial. CSF returns to pre-tap levels in approximately 82 minutes. Thus, the LP has a short-lived effect on symptom management [11,12].
What are treatment options for patients with IIH that present to the ED with headache?
Acetazolamide (Diamox) 250-500 mg BID is recommended and works by decreasing CSF flow. However, because the medication’s effect does not occur until 99.5% of choroid plexus carbonic anhydrase is inhibited, in the acute setting, this may not provide immediate relief .
Furosemide (Lasix) can also treat IIH. Lasix alleviates the headache through diuresis and reducing sodium transport into the brain, thus reducing ICP. Outpatient management generally begins at 20 mg BID dosing .
What are the practice patterns for obtaining an opening pressure in the ED?
There is no data on ED practioners’ frequency of obtaining opening pressure as a part of the LP procedure.
The patient is admitted to neurology for MRI to exclude secondary causes of increased intracranial pressure. MRI is negative. She returns home with neurology follow-up for likely diagnosis of idiopathic intracranial hypertension.
Take Home Points
Lumbar puncture should be performed in the lateral decubitus position to properly obtain an accurate opening pressure if there is concerned for increased ICP. Leg extension may provide a more accurate reading however this is at the expense of increasing procedural difficulty and is not advised currently with the available data.
An opening pressure in adults > 25 cm H20 is abnormal and a broad differential diagnosis should be considered before the diagnosis of idiopathic intracranial hypertension is made.
The use of CSF removal for symptomatic control of IIH is controversial and may not be necessary in the emergency department setting. Starting medications such as acetazolamide and furosemide for IIH should be done in consultation with neurology once other causes of increased ICP have been ruled out.
In emergency medicine practice, most cases of IIH (pseudotumor cerebri) are diagnosed as described in this case – incidentally. The emergent need for LP is quite rare, focusing on time sensitive conditions (meningitis, subarachnoid hemorrhage). The literature regarding the emergent need for LP to rule out IIH is somewhat unclear. For example, I once had a primary care provider send a patient to the ED for “an emergent diagnostic LP to rule out pseudotumor.” His patient presented as an outpatient with blurred vision, a new gradual onset headache, and had recently started an anti-acne medication containing Vitamin A (OCP’s, Vitamin A, tetracycline, and thyroid disorders can all cause IIH). The data/reasoning behind sending this patient to the ER for an emergent LP is murky at best. Could the primary care provider simply have dilated the eyes and look for papilledema? Used an ultrasound if he did not trust his exam? Referred the patient urgently to IR or neurology? Many will opt to simply refer the patient to the ED.
One study shows that patients who experience worsening visual field defects despite medical therapy, or have the presence of visual acuity loss attributed to papilledema, do have improvement in vision following surgical therapy (optic nerve sheath fenestration, shunting, venous sinus stenting) .
Therefore, it seems reasonable that a patient at high risk for IIH who has new visual acuity or field deficits should receive an urgent or emergent LP in combination with an evaluation for papilledema (dilation or ultrasound) in order to properly expedite further care. The time frame within which this needs to occur (urgent vs emergent) is not currently clear. For my personal practice in the community, if your pre-test probability for IIH is high, and your vision is worsening, you will usually get an LP, unless I can arrange for close specialist re-evaluation within 24 hours.
Brian Sellers, MD
Department of Emergency Medicine
Northwestern Medicine Lake Forest Hospital
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