Laboratory Studies
The diagnosis of idiopathic intracranial hypertension (IIH) is made after other causes of increased intracranial pressure (ICP)—such as mass lesions (particularly those involving the midline [eg, medulloblastoma], and causes of recurrent or chronic headache (eg, migraine and hydrocephalus) have been excluded.
Laboratory studies should include evaluation for endocrine abnormalities if such evaluation is indicated by the history or the physical examination findings.
MRI and Ultrasonography
Magnetic resonance imaging (MRI) of the brain with magnetic resonance venography (MRV) is preferred. In children, computed tomography (CT) of the head should be avoided when possible to minimize radiation exposure. The addition of MRV should enable one to exclude thrombosis of a major venous sinus. [6] Stenosis of the transverse sinus is a common finding in IIH but is probably the result of increased ICP. Brain MRI is normal but may show relatively small ventricles. Horev et al demonstrated narrowing of the transverse sinuses in IIH patients. [25] The main finding of their study is the increase in cerebral sinuses diameter after lumbar puncture. This observation should be considered when evaluating cerebral venous sinuses after lumbar puncture. The authors have recommended a larger scale study to validate their findings.
In a study by Gerstl L et al., they suggest that the revised diagnostic criteria for IIH may be too strict, especially in children without papilledema. MRI-based measurement and venous ophthalmodynamometry are promising complementary procedures for monitoring disease progression and response to treatment. [26]
In a study from Shofty et al, pediatric patients with IIH, the optic nerve sheath diameter on MRI is significantly larger than that in healthy controls regardless of age group and sex. [27] This measurement might prove to be an auxiliary tool in the diagnosis of increased ICP in pediatric patients.
Brain imaging should be obtained before a lumbar puncture is performed. Careful measurements of opening and closing pressures should be obtained. Cerebrospinal fluid (CSF) studies yield normal results, except for an elevated opening pressure.
In the emergency department, bedside ultrasonography has been used to identify intracranial hypertension by measuring the diameter of the optic nerve sheath. [28]
Lumbar Puncture
Performing lumbar puncture in children can be challenging and difficult; sedation may be required. CSF pressure may be falsely elevated in a crying child. In addition, no consensus exists as to what constitutes the upper limit of normal for different age groups. [18] In their review, Soler et al [29] gave the following values:
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0-2 years - 75 mm water
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2-5 years - 135 mm water
An intracranial pressure of 280 mm water has recently been established as the upper limit of normal in children. [7]
Diurnal variations in CSF pressure are seen; therefore, the pressure measured at any given time may not reflect the peaks. CSF pressure may be normal in patients with florid papilledema. If the diagnosis of IIH is suspected, repeat lumbar puncture or prolonged pressure monitoring (ie, with a Camino catheter or lumbar pressure catheter) should be considered.
The diagnosis of IIH requires that the CSF be of normal composition with respect to cell count, protein, and glucose.
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For IIH to be diagnosed, brain scans (such as MRI) must be performed to ensure there is no underlying cause for the increased pressure around the brain
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Left optic disc with moderate chronic papilledema in patient with idiopathic intracranial hypertension (pseudotumor cerebri). Paton lines (arc-shaped retinal wrinkles concentric with disc margin) are seen along temporal side of inferior pole of disc.
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Right optic disc with postpapilledema optic atrophy in patient with idiopathic intracranial hypertension (pseudotumor cerebri). Diffuse pallor of disc and absence of small arterial vessels on surface are noted, with very little disc elevation. Disc margin at upper and lower poles and nasally is obscured by some residual edema in nerve fiber layer and gliosis that often persists even after all edema has resolved.
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Most common early visual field defect in papilledema as optic nerve develops optic atrophy is inferior nasal defect, as shown in left eye field chart (left side of figure). Shaded area indicates defective portion of field. Note sharp line of demarcation between defective lower nasal quadrant and normal upper nasal quadrant along horizontal midline. This is characteristic of early papilledema optic atrophy and is referred to as nasal step or inferonasal step.
