Idiopathic Intracranial Hypertension (IIH) Workup

Updated: Oct 08, 2021
  • Author: Mark S Gans, MD; Chief Editor: Andrew G Lee, MD  more...
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Workup

Laboratory Studies

Although routine blood tests are not essential, it is advised that patients with IIH should have a baseline complete blood count, electrolytes, bicarbonate and coagulation profile (PT,PTT).

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MRI and CT Scanning

As mentioned above, patients with bilateral disc swelling should undergo urgent neuroimaging studies to rule out an intracranial mass or a dural sinus thrombosis.  This applies to all patients as even "typical" IIH patients may harbor intracranial pathology.

Brain MRI with gadolinium enhancement and MRV is the study of choice in patients with IIH, in that it provides sensitive screening for hydrocephalus, intracerebral masses, meningeal infiltrative or inflammatory disease, and dural venous sinus thrombosis. Flattening of the globes, an empty sella, distended optic nerve sheaths and slit like ventricles are common neuroradiology findings in IIH. [30]

In addition to a brain MRI, MRV is now becoming the standard of practice in IIH to rule out a dural venous sinus thrombosis. Sagittal T1-weighted images provide excellent views of the superior sagittal sinus, and these should be included in routine brain MRI's. Extraluminal narrowing of the transverse sinuses is a common neuroradiologic finding in IIH. [30]

Brain CT scanning is less expensive than MRI and is usually adequate to rule out an intracranial lesion. However, MRI and MRV are more effective in ruling out a mass lesion and a dural sinus thrombosis, respectively. CT scanning with contrast enhancement may be necessary in patients with contraindications to MRI (ie, pacemakers, metallic clips/foreign bodies).

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Lumbar Puncture

Once an intracranial mass lesion is ruled out, a lumbar puncture is indicated. The opening pressure should be measured with the patient relaxed in the decubitus position to prevent a falsely elevated pressure reading. If any specific difficulty is encountered that may have caused such a false elevation, the clinician performing the procedure must communicate this to the ophthalmologist. Unfortunately, some patients demonstrate a transiently normal pressure despite harboring IIH.  An opening pressure of greater than 25 cm H2O is considered high, however patients with typical presenting symptoms of IIH and normal opening pressures may be considered to have "probable" IIH. [31]

Besides the value of the opening pressure, the clarity and color of the CSF should be noted. In addition, the CSF should be forwarded for cell count, cytology, culture, and measurement of glucose, protein, and electrolyte concentrations. All of these findings are normal in patients with IIH.

In obese patients, finding landmarks may be difficult; consequently, the tap is often performed with the patient seated. The normal CSF pressure at the foramen magnum in the seated position is nearly 50cm H2O from the lumbar entry point in persons of average height. Thus, an opening pressure of 50cm H2O mm water is extremely high for the lateral decubitus position but may be normal for the sitting position. If possible, the patient should be moved to the lateral decubitus position before the pressure is measured.

Another approach to lumbar puncture in obese patients involves fluoroscopic guidance in the radiology department. Prone positioning on the x-ray table and increased abdominal pressure in this position may falsely elevate the CSF pressure. If the pressure is normal with the patient in the prone position, then the measurement is probably accurate. However, if it is high, the patient must be rolled into the lateral decubitus position and allowed to relax before a reliable pressure reading can be completed.

Obviously, such maneuvers carry a risk of displacing the needle from the thecal space. However, no alternative method exists for obtaining an accurate pressure reading.

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