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Allan C. Goncalves, Lucas N. Silva, Eloisa M. Gebrim, Suzana Matayoshi, Mario L. Monteiro; Predicting Dysthyroid Optic Neuropathy by Volumetric Image Analysis of Computed Tomography of the Orbits. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1010.
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© ARVO (1962-2015); The Authors (2016-present)
Dysthyroid optic neuropathy (DON) is the most important complication of Graves’ orbitopathy (GO). It results almost always from optic nerve compression at the orbital apex by enlarged extraocular muscles. The diagnosis of DON rests on several clinical features that may be cumbersome to evaluate, particularly in patients with congestive disease. The use of imaging studies capable of accurately identifying patients prone to develop DON is extremely important to enable timely diagnosis and treatment.The aim of this study was to quantify muscle crowding of orbits with GO with volumetric measurements from axial and coronal planes of Multidetector-row computed tomography (MDCT) images. We calculated indexes from these measurements and analyzed their correlation with DON.
Sixty-nine patients with GO (47 women, 22 men) were prospectively studied. All patients underwent a complete neuro-ophthalmic examination and Visual Field evaluation. Within a period of 2 weeks after the clinical examination, they were scanned on a 16-slice MDCT scanner and the exams were post-processed at a dedicated workstation. With computer assisted measurements two volumetric indexes of muscular crowding were calculated, one from axial scans of the entire orbit content (VCI) and one from coronal scans of the orbital apex posterior to the middle point of the optic nerve (VACI).
Ninety-five orbits of 56 patients with GO met the inclusion criteria and were included in the analysis. 36 were included in the group of orbits with DON and 59 in the group without DON. Both axial volumetric index of orbit muscle crowding (VCI) and volumetric orbital apex crowding index (VACI) showed to be significant different between the groups with and without DON (p < 0.001). VCI showed a reasonable ability to predict DON but VACI, which particularly evaluates the orbital apex showed best results. At a cutoff value of 0.99 VCI showed sensitivity/specificity of 70%/75% positive and negative predictive values of 61% and 80% and accuracy of 72%. The VACI cut off value of 4.14 showed a sensitivity of 92% and a specificity of 86%, positive and negative predictive values of 81% and 94%, and an accuracy of 88% for detecting DON.
This study describes two volumetric indexes of extraocular muscles orbital crowding easily performed in clinical workstations that showed good performance. They lead, particularly VACI, to an improvement in the discrimination ability of patients with DON when compared to previous indexes.
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