Geometric and Volumetric Measurements of Orbital Structures in CT Scans in Thyroid Eye Disease Classification

Abstract

This study examines the usefulness of both geometric and volumetric measurements of orbital soft tissues on CT scans to provide quantitative diagnostic guidance in image reading of thyroid eye disease (TED). Computed tomography (CT) images were obtained from 92 orbits and were classified as impaired motility (TED-IM) and normal motility (TED-NM). The TED-IM group was further divided into dysthyroid optic neuropathy (DON) and non-DON groups. There were 5 volumetric, 2 angular, and 3 ratio parameter measurements acquired from CT images to examine their feasibility in TED classification. We found that the mean volumes of extraocular muscle and retroorbital fat and their ratio to the orbital volume were significantly different between the two motility groups. The mean ratio of extraocular muscle volume in orbital apex and orbital apex volume (EMV-OA/OAV) was significantly larger in DON than non-DON patients (p < 0.05). The population distribution among TED-NM, non-DON, and DON groups significantly varied for different angles between the optic nerve and medial rectus and lateral rectus. In conclusion, geometric and volumetric measurements using CT scans help to quantitatively classify TED.

Surgical Outcomes of Standardized Endoscopical Deep Medial Orbital Decompression in Dysthyroid Optic Neuropathy

“…The measurement method is consistent with the published literature 10 . We focused on comparing orbital parameters found in previous studies that re ect compression of the orbital apex.…”

“…At the base of our preliminary study 20 , we noticed that the differences between the DON patients and non-DON patients were mainly concentrated in the orbital apex, which indicated that orbital apex congestion, especially the pressure from the medial wall was the primary cause of DON. In this study, we propose and emphasize the importance of deep orbital decompression (up to the orbital apex and the orbital part of the optic canal) in patients with DON.…”

“…Additionally, we compared the EMV-OAV/OAV with non-DON patients using data published 10 . We discovered that there was no signi cant difference between the DON patients postoperatively and the non-DON patients (P = 0.3383) (Figure 2 F).…”

“…In our preliminary study, we compared the differences in orbital parameters between DON and non-DON patients through CT scans and found the primary site causing DON was in the orbital apex, where the enlarged extraocular muscle compressed the optic nerve 10 . This evidence suggests that an effective surgery should be able to relieve the compression of the optic nerve in the orbital apex.…”

RAPD as a clinical alert for early evidence of dysthyroid optic neuropathy

“…Volumetric measurements of extraocular muscle tissues can demonstrate the condition of apical crowding in a quantitative way and have been used as an indicator of DON. [ 25 ] Our case 1 right eye had grade 3 and left eye grade 2 apical crowding [ Figure 3a ]. In case 2, both eyes had grade 2 apical crowding [ Figure 6a ].…”