Graves Ophthalmopathy: The Bony Orbit in Optic Neuropathy, Its Apical Angular Capacity, and Impact on Prediction of Risk

Abstract

BACKGROUND AND PURPOSE:Optic neuropathy (ON), a serious complication of Graves ophthalmopathy, is often subclinical and masked by symptoms of orbitopathy. We examined herein bony and soft-tissue CT features associated with ON, including an angular assessment of orbital apex capacity, and their usefulness in the risk prediction of ON.

Quantification of Orbital Apex Crowding for Screening of Dysthyroid Optic Neuropathy Using Multidetector CT

“…In our study, although the subjective orbital apex CI detected DON with 80.6% sensitivity for scores 1 or 2, none of the 36 affected orbits presented grade 3 apical crowding. These findings are remarkably different from previous studies using the Nugent subjective score to detect DON, 1,3,9,15 probably due to differences in subjective criteria for defining and grading apical crowding. While it seems clear that the Nugent apical crowding score is useful to raise suspicion of the presence of DON, it does not provide a clear definition of the position along the orbit where the coronal plane is used to determine it, nor does it provide a clear differentiation between grades 1, 2, and 3.…”

“…Other researchers have reached similar conclusions. 1,9 Finally, our study shows that CI is more efficient at detecting DON than the linear muscle index described by Barrett et al 10 In their study, a muscle index of 67% or greater indicated compressive neuropathy and had a diagnostic sensitivity of 67%. 10 In a previous study using MDCT to determine the sensitivity and specificity of the muscle index in a similar set of patients, we found that a muscle index of 60% provided the best combination of sensitivity/specificity (79% and 72%, respectively).…”

“…The theory is based mostly on CT imaging studies confirming the presence of orbital apex crowding in most patients with DON. 10,12,13,18,19 Because of its great importance in DON, apical crowding is quantified with a score first described by Nugent et al 15 and reproduced by many other authors, 1,3,7,9,16 which grades the effacement of the perineural fat as 0 (none), 1 (up to 25%), 2 (25%-50%), or 3 (greater than 50%). 15 Using this method, Nugent et al found severe apical orbital crowding (grade 3) in 12 of 18 orbits with DON but in only 16 of 124 orbits without DON.…”

“…Because the prognosis of DON improves significantly with early diagnosis and treatment, much effort has been placed on designing objective tests capable of identifying patients at high risk for developing DON. 9 CT is the preferred imaging technique for investigating DON. 1 Several studies have tested the ability of CT parameters (linear, 3,[9][10][11] area, and volume [12][13][14] measurements of the orbital muscles) to facilitate the diagnosis of DON.…”

“…9 CT is the preferred imaging technique for investigating DON. 1 Several studies have tested the ability of CT parameters (linear, 3,[9][10][11] area, and volume [12][13][14] measurements of the orbital muscles) to facilitate the diagnosis of DON. Most of these studies used axial and direct or reformatted coronal images acquired with conventional CT scanners, and calculations were often performed manually from hard copies of the scans.…”