The effect of CSF drain on the optic nerve in idiopathic intracranial hypertension

Abstract

Background: Elevation of intracranial pressure in idiopathic intracranial hypertension induces an edema of the prelaminar section of the optic nerve (papilledema). Beside the commonly observed optic nerve sheath distention, information on a potential pathology of the retrolaminar section of the optic nerve and the short-term effect of normalization of intracranial pressure on these abnormalities remains scarce.

Methods: In this exploratory study 8 patients diagnosed with idiopathic intracranial hypertension underwent a MRI scan (T2 mapping) as well as a diffusion tensor imaging analysis (fractional anisotropy and mean diffusivity). In addition, the clinical presentation of headache and its accompanying symptoms were assessed. Intracranial pressure was then normalized by lumbar puncture and the initial parameters (MRI and clinical features) were re-assessed within 26 h.

Results: After normalization of CSF pressure, the morphometric MRI scans of the optic nerve and optic nerve sheath remained unchanged. In the diffusion tensor imaging, the fractional anisotropy value was reduced suggesting a tissue decompression of the optic nerve after lumbar puncture. In line with these finding, headache and most of the accompanying symptoms also improved or remitted within that short time frame.

Conclusion: The findings support the hypothesis that the elevation of intracranial pressure induces a microstructural compression of the optic nerve impairing axoplasmic flow and thereby causing the prelaminar papilledema. The microstructural compression of the optic nerve as well as the clinical symptoms improve within hours of normalization of intracranial pressure.

Keywords: DTI; Idiopathic intracranial hypertension; Intracranial pressure; Lumbar puncture; MRI; Optic nerve.

Fig. 1

a shows an example of a coronal T2w image of the ON and ONS on which ON and ONS diameters where calculated. b shows the coronal T2-mapping. c illustrates the DTI measurements of the ON and depicts an MR-tractography of the ON

Fig. 2

Illustrates the variation in the FA a and MD b values prior and after normalization of CSF pressure through lumbar puncture. The FA value was significantly reduced after normalization of CSF pressure (p = 0.038)

Fig. 3

Illustrates the changes in ON a and ONS b diameters as well as in T2 values c before and after normalization of CSF pressure. The normalization of CSF pressure did not induce a significant change in any of the three parameters (ON p = 0.130, ONS p = 0.798, T2 p = 0.310)

Fig. 4

Depicts the correlations between the difference in FA value and CSF pressure a as well as between the difference of FA values and headache intensity b before and after normalization of CSF pressure. In both cases correlations were not significant (p > 0.05)