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R Siddiqi, PA Good, MD Tsaloumas; Ocular Echography in the diag . Invest. Ophthalmol. Vis. Sci. 2002;43(13):239.
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Purpose: Bilateral fluid distension of the optic nerve sheath in the presence of disc elevation in an echographic sign of papilloedema. However, false positives can occur because fluid distension of the optic nerve sheath is present in individuals who have no elevation of intracranial pressure ICP. The aim of this study is to compare individuals with flat discs, those with papilloedema due to disc drusen and those with clinically proven benign intracranial hypertension (BIH). Methods: 50 normal adults with flat or slightly cupped discs underwent echographic cross-sectional imaging of the optic nerve, and were compared to 20 patients with disc drusen and 40 patients with BIH. Standardised A and B scan echography was performed on each eye with the probe held vertically at the lateral canthus and the eye in primary position. Results: Of the 100 eyes with flat or slightly cupped discs only 7 (7%) showed any evidence of distension of the dural sheath with a mean inner dural diameter IDD of 2.7 cm and a mean IPD/ IDD ratio of 0.97. Of the 40 eyes with buried disc drusen 5 eyes (12.5 %) had fluid distension of the nerve sheath with a mean IDD of 2.5 cm and IPD/ IDD ratio of 0.96. In the group with BIH 76 eyes showed fluid distension of the sheath (95 %) with a mean IDD of 4.53 and a mean IPD/IDD ratio of 0.55. The mean CSF opening pressure in those patients was 32.8 cms H20. Conclusion: In this study fluid distension of the nerve sheath measured echographically occurs in 95 % of patients with BIH (i.e. genuine papilloedema) but in only 7 % of patients with flat discs. In disc drusen the specificity is a little higher at 12.5 %. This indicates that echographic analysis of the optic nerve is a sensitive indicator of true papilloedema, but in pseudo-papilloedema false positives can occur and therefore the findings should be considered with caution.
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