Predicting dysthyroid optic neuropathy using computed tomography volumetric analyses of orbital structures

Abstract

OBJECTIVE:To evaluate the ability of orbital apex crowding volume measurements calculated with multidetector-computed tomography to detect dysthyroid optic neuropathy.METHODS:Ninety-three patients with Graves' orbitopathy were studied prospectively. All of the patients underwent a complete neuro-ophthalmic examination and computed tomography scanning. Volumetric measurements were calculated from axial and coronal contiguous sections using a dedicated workstation. Orbital fat and muscle volume were estimated on the basis of their attenuation values (in Hounsfield units) using measurements from the anterior orbital rim to the optic foramen. Two indexes of orbital muscle crowding were calculated: i) the volumetric crowding index, which is the ratio between soft tissue (mainly extraocular muscles) and orbital fat volume and is based on axial scans of the entire orbit; and ii) the volumetric orbital apex crowding index, which is the ratio between the extraocular muscles and orbital fat volume and is based on coronal scans of the orbital apex. Two groups of orbits (with and without dysthyroid optic neuropathy) were compared.RESULTS:One hundred and two orbits of 61 patients with Graves' orbitopathy met the inclusion criteria and were analyzed. Forty-one orbits were diagnosed with Graves' orbitopathy, and 61 orbits did not have optic neuropathy. The two groups of orbits differed significantly with regard to both of the volumetric indexes (p<0.001). Although both indexes had good discrimination ability, the volumetric orbital apex crowding index yielded the best results with 92% sensitivity, 86% specificity, 81%/94% positive/negative predictive value and 88% accuracy at a cutoff of 4.14.CONCLUSION:This study found that the orbital volumetric crowding index was a more effective predictor of dysthyroid optic neuropathy than previously described computed tomography indexes were.

Structural functional associations of the orbit in thyroid eye disease: Kalman filters to track extraocular rectal muscles

“…The results of univariate correlations for orbital metrics (including orbital volume, volumetric crowding index[15], and proptosis) and optic nerve metrics (include length, cross sectional area, volume, and diameter) are shown in Table 1. Similarly, the correlations for clinical characteristics with muscle metrics are shown in Table 2.…”

“…Therefore, distinct structures such as globe, nerve, muscle, and fat can be identified with a high accuracy. Extraocular muscle, bone, fat, and orbital volume indices are among the metrics used in previous study[2–15] as objective findings used to aide in early diagnosis.…”

Introductory Chapter: The Dysthyroid Optic Neuropathy

“…More recently, imaging studies, such as computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US), and colour Doppler imaging (CDI), can also be extremely important in both the diagnosis and clinical or surgical follow-up [3].…”

“…They found that patients with Graves' orbitopathy who have severe optic nerve crowding, intracranial fat prolapse and/or muscle index greater than 50% present on orbital CT scans are more likely to have coexisting optic neuropathy. An important result to cite is due to Goncalves et al [3], who targeted at assessing the ability of multi-detector CT to detect DON. The proposed study involved 93 patients who underwent a complete neuro-ophthalmic examination, as well as a CT scan.…”

“…The GO can have a major impact on the patient life, from both functional and aesthetic point of view; to some extent, it can be considered as an event deeply affecting the quality of life of the patients. The most serious consequence of GO is perhaps the dysthyroid optic neuropathy (DON), which is due to compression caused by the swelling of extraocular muscles and orbital fat [3].…”