Increased Intracranial Pressure

Shawn Aylward
Increased Intracranial Pressure - Diagnosis
The ophthalmic exam is a fundamental part of the diagnosis and management of intracranial hypertension. Direct funduscopic exam of the optic nerves should be performed at each visit to assess for the presence of edema. The degree of edema is graded using the Frisén scale, ranging from 0 (normal) to grade 5 (severe).(24) Spontaneous venous pulsations (SVPs) at the optic nerve head have been evaluated as a marker for increased intracranial pressure. They have been documented in those with documented elevated intracranial pressure and absent in normal individuals. Thus decisions regarding work up and even treatment should not hinge upon the presence or absence of SVPs.
Humphrey or Goldmann visual fields are used to assess for visual field deficits seen with intracranial hypertension. Humphrey field testing is an automated test, but unfortunately requires maintaining concentration. Some younger children can be assessed with Goldmann testing when they are unable to complete Humphrey field testing. An enlarged blind spot is the most common visual field defect. Peripheral constriction, paracentral scotoma, nasal field loss, and inferior arcuate defects are also seen.

B-scan ultrasound is used to detect calcified optic nerve head drusen, and thus differentiate true papilledema from pseudo-papilledema. However, in younger patients drusen may not yet contain calcification and is only detectable by fundus autofluorescence photography.

Neuroimaging should include MRI and MRV to rule out secondary causes. Subtle findings seen by the astute practitioner can include partially empty sella turcica, flattening of the posterior globe, dilation of the optic nerve sheath, slit-like ventricles, distal transverse sinus stenosis, anterior protrusion of the optic nerve head, and tortuosity of the optic nerve. Presence of one or more of these radiographic findings greatly increases the probability of having intracranial hypertension. However, the probability does not decrease in absence of these findings.

The final diagnostic component is the lumbar puncture. Proper positioning includes lateral decubitus with the legs and head extended at the time of measurement. Popular convention dictates withdrawal of large CSF volumes to return the pressure to normal and help protect the vision. Johnston and colleagues achieved a normal pressure in a series of adult PIH patients through removal of 15-25 ml of CSF. Using continuous pressure monitoring, they followed the time to return of their initial pressure, which averaged 82 minutes.(25) Thus there is questionable benefit to achieving a normal pressure in these patients.
Studies on adult normative values for CSF opening pressure have consistently shown that the pressure must be in excess of 25cm H20 to be considered abnormal.(26-28) There has been no correlation found with the degree of obesity and opening pressure.(26, 28) Due to ethical considerations there have not been many pediatric studies. Based on the few published works, some practitioners use >18 cm H20 for children under 8 years of age and >25 cm H20 for children 8 years or above or <8 in absence of optic nerve edema as abnormal.(29)

Two recent articles that have questioned the use of these values.(30, 31) Avery et al. performed an analysis of patients receiving lumbar punctures as part of their workup for other conditions.(30) They observed a mean opening pressure of 19.8 cm H20 and an upper limit of normal (i.e. the 90th percentile) of 28 cm H20. Lee et al. studied 44 patients who had a sedated lumbar puncture and found a mean of 20.3 cm H20.(31) Both studies included patients with demyelinating and white matter disease in their normal patient sample (discussion is found in the online appendix for Avery et al.). In a separate analysis of the patients with demyelinating disease, Lee et al. found a mean opening pressure of 21.5cm H20, which is higher than their total population mean (20.3 cm H20).(31) Other published studies have shown patients with demyelinating disease have higher opening pressures.(32-34) Thus inclusion of these patients in a normal population sample could result in a skewed average.

Increased Intracranial Pressure Increased Intracranial Pressure 04/20/2016
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