Does IIH Alter Brain Microstructures? - A DTI-Based Approach

Effect of General Anesthesia on MR Optic Nerve Sheath Diameter in the Pediatric Population

BACKGROUND

Papilledema is thought to be the hallmark sign of increased intracranial pressure (ICP). Distension of the subarachnoid space within the optic nerve sheath is also commonly reported in MR studies as an indirect sign of increased ICP.

HYPOTHESIS

General anesthesia and positive pressure ventilation might result in changes in optic sheath diameter (OSD) observed on clinical brain MRI.

STUDY TYPE

Retrospective.

POPULATION

One hundred forty-five  patients (154 MRI scans, 7.3 years ± 5.1); 97 studies in the anesthesia group (4.4 years ± 3.4) of which 22 had papilledema, and 57 in the non-anesthesia group (12.3 years ± 3.2), of which 28 had papilledema.

FIELD STRENGTH/SEQUENCE

1.5T or 3.0T volumetric T2 images. T2 images were obtained from different vendors.

ASSESSMENT

OSD, optic nerve diameter (OND), and peri-optic cerebrospinal fluid (CSF) were measured manually on T2-weighted MR images for various population subgroups (with and without anesthesia; with or without papilledema). The correlation between these measurements and the clinical diagnosis of papilledema was evaluated via receiver operating characteristic (ROC) analysis.

STATISTICAL TESTS

Chi-square test; Mann-Whitney Test; Spearman's test and ROCs; Interclass correlation coefficient, P = 0.05.

RESULTS

General anesthesia resulted in significantly larger mean OSD in patients with or without papilledema (7.3 ± 1.0 mm vs. 6.1 ± 1.1 mm and 6.7 ± 1.0 mm vs. 5.4 ± 0.9 mm, respectively). In the non-anesthesia group, the average OSD values (6.1 ± 1.1 mm) were significantly higher in papilledema patients compared to non-papilledema patients (5.4 ± 0.9 mm), with larger peri-optic CSF rim (1.6 ± 0.4 mm vs. 1.3 ± 0.3 mm). In the anesthesia group, OND was significantly larger in papilledema patients (3.4 ± 0.4 mm vs. 3.1 ± 0.5 mm), though the average peri-optic CSF rim did not reach a significance in papilledema compared with non-papilledema patients (2.0 ± 0.3 mm vs. 1.8 ± 0.4 mm, P = 0.06). In patients with general anesthesia, peri-optic CSF rim had a limited correlation with increased ICP.

DATA CONCLUSION

In the pediatric population, imaging findings of increased OSD on brain MRI might be related to general anesthesia rather than increased ICP. The interpretation of optic nerve sheath distention should be reported cautiously in conjunction with anesthesia status, especially in the pediatric population.

EVIDENCE LEVEL

4 Technical Efficacy: 5.

Diffusion-tensor MR imaging of optic pathway in idiopathic intracranial hypertension

PURPOSE

To investigate the role of diffusion tensor imaging (DTI) of optic pathway in patients with idiopathic intracranial hypertension (IIH).

PATIENTS AND METHODS

This study included 41 IIH patients and 22 controls. They underwent DTI of the optic nerve (ON) and optic radiation (OR). Their fractional anostrophy (FA) and mean diffusivity (MD) were calculated by two reviewers and correlated with papilledema grade.

RESULTS

The optic nerve mean FA and MD of patients for reviewer-1 were 0.21 ± 0.047 and 2.189 ± 0.52 ×10-3 mm2/s and for reviewer-2 were 0.216 ± 0.047 and 2.17 ± 0.54 ×10-3 mm2/s. The mean ON FA and MD of controls for reviewer-1 were 0.33 ± 0.048 and 1.29 ± 0.26 ×10-3 mm2/s and for reviewer-2 were 0.34 ± 0.05 and 1.3 ± 0.26 ×10-3 mm2/s. There was significant difference in FA and MD between patients and controls (p < 0.00001). The OR mean FA and MD of patients for reviewer-1 were 0.61 ± 0.03 and 2.26 ± 0.55 ×10-3 mm2/s and for reviewer-2 were 0.6 ± 0.03 and 2.24 ± 0.57 ×10-3 mm2/s The mean OR FA and MD of controls for reviewer-1 were 0.6 ± 0.03 and 2.19 ± 0.49 ×10-3 mm2/s and for reviewer-2 were 0.6 ± 0.03 and 2.18 ± 0.49 ×10-3 mm2/s. There was no significant difference in FA and MD obtained in patients and controls. Both the FA and the MD of the ON showed strong correlation with the papilledema grade (r = -0.8 and 0.951, respectively).

CONCLUSION

Our findings suggest that, IIH is associated mainly with pre-chiasmatic or ON involvement rather than post-chiasmatic parenchymal or OR involvement. DTI MD and FA parameters of the ON may be a reliable imaging biomarker for diagnosis of IIH and well correlated with papilledema grades.

Extent of transverse sinus stenosis does not predict visual outcomes in idiopathic intracranial hypertension

BACKGROUND

We aimed to investigate whether the degree of transverse sinus stenosis (TSS) on magnetic resonance venography (MRV) can predict visual outcomes in patients with idiopathic intracranial hypertension (IIH).

METHODS

A chart review identified IIH patients followed for at least 6 months. Mean deviation (MD) on visual field (VF) testing at initial and last follow-up visits, best corrected visual acuity (BCVA), patients' age, body mass index, and lumbar puncture opening pressure were recorded. MRV was used to grade TSS on a scale of 0-8 using the grading scheme proposed by Farb et al., whereby a lower score indicates a greater degree of stenosis. Linear regression analysis was used to test for association between above variables and MD on VF, including change in MD over time.

RESULTS

44 female patients were followed for a median of 26 months. All patients had unilateral or bilateral TSS on MRV. The median TSS score was 3/8. The median BCVA was 0.06 logMAR at baseline. The median VF MD was -3.02 dB at baseline and -1.96 dB at final follow-up. There was no significant association between the degree of TSS and either baseline MD (P-value = 0.34) or the change in MD on VF over the course of follow-up (P-value = 0.54). Baseline BCVA (P = 0.045) and baseline MD (P < 0.001) were the only significant predictors of changes in MD on VF over follow-up.

CONCLUSIONS

Baseline BCVA and MD on VF were the only significant predictors of visual outcome in IIH patients. While all patients demonstrated TSS on MRV, the degree of TSS did not correlate with visual prognosis.

Pathogenesis and Evaluation of the Effects of Idiopathic Intracranial Hypertension on the Optic Nerves

Idiopathic intracranial hypertension (IIH) is a clinical syndrome of raised intracranial pressure of unknown aetiology. Although papilloedema and visual alterations are among the most important manifestations of the disease, their pathophysiological mechanisms are not fully understood. We aim to review the up-to-date evidence regarding how the optic nerves are affected, the possible pathophysiology and the methods of their assessment.

An Update on Imaging in Idiopathic Intracranial Hypertension

Neuroimaging plays an essential role in the diagnostic workup of idiopathic intracranial hypertension with the aims to exclude secondary causes of elevated intracranial pressure and to identify imaging signs that are commonly observed in this disorder. As a valuable expansion of brain imaging, the imaging of the retina using optical coherence tomography has been of increasing value. In particular, this is the case with the latest devices that allow a more accurate distinction between a reduction in retinal nerve fiber layer thickness due to an improvement of papilledema or due to a worsening caused by optic nerve atrophy. Although optical coherence tomography does not yet replace the other elements of the diagnostic workup, it is likely to play an increasing role in diagnosis and follow-up of idiopathic intracranial hypertension. The review focuses on the main findings in neuroimaging, including structural and vascular alterations as well as on the relevance of optical coherence tomography.

Lumbar puncture rapidly improves olfaction in patients with idiopathic intracranial hypertension: A cohort study

BACKGROUND

A lumbar puncture constitutes an important diagnostic procedure in the evaluation of idiopathic intracranial hypertension. Chronic overflow of cerebrospinal fluid into the sheaths of the olfactory nerves appears to be related to olfactory impairment in these patients. Here, we asked whether cerebrospinal fluid drainage in idiopathic intracranial hypertension patients improves olfactory function.

METHODS

Fourteen idiopathic intracranial hypertension patients and 14 neurologic control patients were investigated before and after lumbar puncture using the extended Sniffin' Sticks procedure. We assessed odor threshold, discrimination, and identification. In idiopathic intracranial hypertension patients, cerebrospinal fluid was drained until cerebrospinal fluid pressure had normalized. In addition, a third group of 14 healthy controls participated in the two smell tests at similar intervals.

RESULTS

Relative to healthy controls, threshold, discrimination, and identification composite scores before lumbar puncture were significantly lower in idiopathic intracranial hypertension patients and also in neurologic controls. Following lumbar puncture, threshold, discrimination, and identification scores for neurologic controls remained unchanged whereas idiopathic intracranial hypertension patients showed robust improvement on the composite score as well as on all three subscores (all changes: p < 0.003), quickly regaining olfactory function in the normal range. Cerebrospinal fluid opening pressure was significantly correlated with improvement in threshold, discrimination, and identification score upon cerebrospinal fluid drainage (r = 0.609, p = 0.021).

CONCLUSION

Olfactory impairment is an important, yet underappreciated, clinical feature of idiopathic intracranial hypertension. Lowering of increased intracranial pressure improves hyposmia. Our findings shed new light on the pathophysiology of cerebrospinal fluid circulation in idiopathic intracranial hypertension.

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

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.