Evidence for Larger Extra Ventricular Cranial CSF Volume in Idiopathic Intracranial Hypertension (IIH)

Abstract

 

Purpose:

 

To study MRI-derived measures of total cranial, ventricular and extra-ventricular cerebrospinal fluid (CSF) volumes in IIH. If IIH is indeed associated with impaired CSF absorption, an increased extra-ventricular CSF volume is expected.

 

Methods:

 

We prospectively studied MRI scans of 14 women with newly-diagnosed untreated IIH before the diagnostic spinal tap and 11 healthy women of similar age, gender and BMI (Table). The diagnosis of IIH was made using the modified Dandy criteria. The CSF opening pressures were mean 37.38 + 6.42 cm water, range 26 - 47. Papilledema modified Frisen grading range from grade 1 to 5, and Humphrey 30-2 SITA standard perimetry mean defects were -3.17 + 2.70 dB, range -0.25 to -7.84. Quantification of intracranial CSF volumes was achieved using whole brain T1-weighted MRI and the FSL software package. Intraventricular CSF volumes were measured using the 3D Slicer software program. The extra-ventricular CSF volume in the brain was calculated as the numerical difference between the intracranial and intra-ventricular CSF volumes.

 

Results:

 

Mean intracranial CSF volume of IIH patients were significantly greater compared to controls (Table, P < 0.01, two tail t-test). Specifically, the extra-ventricular CSF space was significantly larger in the patient group (P < 0.01). The ventricular sizes were similar between the two groups (p=0.735), in agreement with recent reports.

 

Conclusions:

 

Patients with IIH have larger quantitated global cranial CSF volumes compared to controls supporting that IIH is associated with impaired CSF absorption as described by other studies. The extra ventricular accumulation of CSF is consistent with findings of CSF accumulation in the optic nerves sheath in IIH and is also consistent with recently reported lower spinal canal compliance in IIH, which explains why the increased CSF volume accumulates in the cranial compartment.  

 

Keywords: neuro-ophthalmology: optic nerve • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)