Analysis Of Bony Orbital Volume Changes And Related Factors After Endoscopic Orbital Decompression For Thyroid-associated Ophthalmopathy

Objectives:Using CT scanning images and computer-aided measurement software Mimics17.0 to reconstruct 3D models of the orbital,the orbital parameters of patients with thyroidassociated ophthalmopathy（TAO）that were treated with endoscopic orbital decompression were quantitatively measured.Besides,the bony orbital volume（BOV）of patients was analysed before and after surgery and the related influencing factors were explored.This study aims to provide a valuable reference for the precise treatment of TAO by endoscopic orbital decompression.Methods:The data of 42 eyes from 23 patients who were diagnosed with TAO and subsequently received endoscopic orbital decompression in The Second Hospital Of Jilin University from June 2019 to October 2021 were selected.In addition to the patients’ clinical data,CT scan images were collected.Mimics 17.0 computer-aided measurement software was used to reconstruct a 3D model of the orbital bone wall and orbital soft tissue,and the BOV values before and after surgery were measured.Subsequently,the correlations between various parameters such as proptosis,decompression range（comprising decompression length,height,and area）,tissue prolapse depth,ethmoid sinus volume（including ethmoid sinus length,width,height）,and variations in BOV were analyzed.Statistical analysis was performed using SPSS25.0 software.Results:1.Differences in bony orbital volume before and after surgery: the mean preoperative BOV was 24.79 ± 2.24 cm3,and the mean postoperative BOV was 27.95 ± 2.52 cm3.The post-surgery BOV was substantially higher than the preoperative BOV and the difference was statistically significant（P < 0.001）.The mean BOV increase was 3.11 ± 1.52 cm3,representing a 12.55% rise in orbital volume after surgery.2.Changes in proptosis before and after surgery: the mean preoperative proptosis was 22.9 ± 3.74 mm,and the mean postoperative proptosis was 19.67 ± 3.72 mm.The postsurgery proptosis was substantially lower than the preoperative,and exhibiting a statistically significant difference（P < 0.001）.Reduction in proptosis value was 3.3 ± 1.5mm.3.Correlation analysis of BOV increment: the decompression area,length,height and tissue prolapse depth were positively correlated with BOV increment,and the correlation coefficients were r = 0.813,0.663,0.565,and 0.474.Besides,all of these results had statistical significance（all P values < 0.05）.Additionally,the ethmoid sinus volume,length,and width were positively correlated with BOV increment,with correlation coefficients were r = 0.702,0.441,and 0.453,respectively.These values were also statistically significant（all P values < 0.05）.In contrast,the progression of TAO and the time of thyroid dysfunction were negatively correlated with BOV increment.The correlation coefficients were r = 0.616 and 0.526,respectively,exhibiting statistically significant difference（both P values < 0.01）.However,there was not a significant correlation between the BOV increment and the patient’s height,weight,age or ethmoid sinus height（all P values > 0.05）.4.A multiple regression analysis was performed to determine the impact of multiple factors on BOV increment and it was found that decompression area（β= 0.605）had a greater influence on BOV increment than ethmoid sinus volume（β= 0.255）.Furthermore,a linear regression equation was obtained for predicting the volume increment（y）of the bony orbit:y=2.225×decompression length+2.817×ethmoid sinus width-4.814（r=0.739）Conclusions:1.Endoscopic orbital decompression can significantly increase the bony orbital volume,resulting in retraction of the eyeball and improving exophthalmos appearance in TAO patients.2.The range of decompression and the volume of ethmoid sinus are important factors that affect the BOV increment after endoscopic orbital decompression.Of these,the length of decompression and the width of the ethmoid sinus have the most significant influence on the BOV increment.3.The approach used in this study concerning the quantitative measurement of orbital parameters using computer-aided software can also be applied to other orbital decompression operations,so as to quantify surgical results and provide a theoretical basis for accurate and personalized treatment.