Effect of changes in optic nerve elasticity on central retinal artery blood flow in patients with idiopathic intracranial hypertension

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.

Non-invasive intracranial pressure assessment using shear-wave elastography in neuro-critical care patients

OBJECTIVE

To determine if Young's modulus of the optic nerve (ON) structure as measured by shear-wave elastography can suggest changes in intracranial pressure (ICP) in neuro-critical care patients.

MATERIALS AND METHODS

Thirty-one healthy volunteers and twenty-two neuro-critical care patients were enrolled. ON sheath (ONS) diameter (ONSD) values and Young's modulus measurements of volunteers were collected in a calm state and during a Valsalva maneuver (VM). Ultrasound measurements and ICP values of patients were collected on operation day and at 24 and 48 h after the operation; measurements were thereafter assigned to three groups: severely elevated (ICP greater than 22 mmHg), mildly elevated (ICP = 14-22 mmHg), and normal (ICP ≤ 13 mmHg).

RESULTS

ONSD and Young's modulus for the ON and ONS of volunteers during VM were higher than those in the calm state (all P < 0.001). In contrast to ONSD, Young's modulus for ON and ONS did not correlate with age, body mass index, or sex. The best cutoff values of Young's modulus for ON for predicting elevated and severely elevated ICP were 16.67 kPa and 22.74 kPa, respectively. Accordingly, the sensitivity values were 96.7% and 88.9%, and the specificity values were 86.1% and 73.7%, which had the same diagnostic performance as ONSD.

CONCLUSION

Young's modulus of the ON accurately reflects changes in ICP. It is not confounded by age, sex, or body mass index compared to ONSD.

Evaluation of 2D FLAIR hyperintensity of the optic nerve and optic nerve head and visual parameters in idiopathic intracranial hypertension

BACKGROUND AND PURPOSE

T2/FLAIR hyperintensity of the optic nerve/optic nerve head has been described as a sensitive finding in idiopathic intracranial hypertension using post-contrast 3D-T2/FLAIR imaging. The purpose of this study is to assess whether hyperintensity on non-enhanced 2D-T2/FLAIR imaging occurs more likely in diseased patients than controls and to evaluate the relationship between FLAIR signal and visual parameters MATERIALS AND METHODS: A retrospective case-control study was performed of patients with idiopathic intracranial hypertension and controls who underwent orbital MRI. Three neuroradiologists reviewed the FLAIR images, subjectively evaluating for hyperintense signal within the optic nerves/optic nerve heads using a 5-point Likert Scale. Quantitative assessment of optic nerve signal using regions of interests was performed. Clinical parameters were extracted. The diagnostic performance was evaluated, and Spearman correlation calculated to assess the relationship between FLAIR signal and visual outcomes.

RESULTS

The sensitivity of abnormal FLAIR signal within the optic nerves and optic nerve heads in patients with idiopathic intracranial hypertension ranged from 25-54% and 4-29%, respectively, with specificities ranging from 67-92% and 83-100%. Quantitative assessment revealed a significant difference in CNR between cases and controls in the left posterior optic nerve (p=.002). A positive linear relationship existed between abnormal optic nerve head signal and papilledema grade (OD: p=.02, OS: p=.008) but not with other visual parameters.

CONCLUSION

T2/FLAIR hyperintensity in the optic nerve/optic nerve head may support the diagnosis of idiopathic intracranial hypertension but its absence should not dissuade it. If present, abnormal signal in the optic nerve head correlates with papilledema.