Abstract Listings 2024

Purpose

Orbital decompression surgery is performed in patients with thyroid eye disease (TED) who have compressive optic neuropathy, exposure keratitis or proptosis. Lateral orbital wall decompression is commonly performed by oculoplastic surgeons due to greater reduction in proptosis and fewer complications than other techniques. The size of the sphenoid trigone to be removed is the key concept in the efficacy of decompression and the rate of complications. This study aims to describe the characteristics of sphenoid trigone from computed tomography (CT) scans of the brain in Thai population. To the best of our knowledge, this is the first study reports the measurements of sphenoid trigone parameters of the orbit with CT- based in Thailand.

Methods

A single-center retrospective observational pilot study based on CT scans; Inclusion criteria included the Thai population aged 60 years or older with no orbital diseases, no drugs affecting bone metabolism and no history of maxillofacial trauma or surgery. All images were obtained from a 3-mm. slice thickness CT scan of the brain using a PACs system. The sphenoid trigone was identified in the axial scan extending from the superior orbital fissure to the inferior orbital fissure. The region of interest (ROI) of each slice of the right and left sphenoid was manually outlined with software, and volume was calculated based on the slice thickness (3 mm). The perpendicular and diagonal depths of the orbital walls were measured using the most superior portion of the optic canal on the axial view. All measurements were performed by one author and repeated by another author for repeatability, with intraclass correlation coefficient (ICC) calculated.

Results

One hundred and twelve orbits of 56 patients were included. There were 31 males (55.36%) and 25 females (44.64%) with no significant difference (p=0.953). The average ROI (mean ± SD) was 1.17 ± 0.40 cm2 on the right and 1.27 ± 0.46 cm2 on the left. The mean calculated sphenoid trigone volume on the right side did not significantly differ from the left; 14.89 ± 5.23 cm3 and 15.48 ± 6.35 cm3 respectively. The average Hounsfield units (HU), which represent cortical bone density, were 417.18 ± 142.96 HU on the right and 400.39 ± 145.71 HU on the left. Additionally, the mean perpendicular orbital depth was 2.85 ± 0.40 cm on the right and 2.87 ± 0.41 cm on the left, while the diagonal orbital depth was 3.56 ± 0.50 cm. on the right and 3.56 ± 0.46 cm. on the left respectively. There were no significant differences in orbital depth between sexes or sides of the orbit. With the repeatability of measurements in this study, good inter-user variability and agreement were found with the intraclass correlation coefficient (ICC) calculated for all measurements.

Conclusion

In this study, the authors utilized CT brain imaging with a slice thickness of 3 mm, which is widely available in most hospitals in Thailand. There were no significant differences in ROI, volume, HU, and orbital depths between the left and the right sides in this pilot study. Similarly, both perpendicular and diagonal orbital depths did not show significant differences between sexes. This lack of significant difference is likely related to the small subject number or errors in the measurement technique. The authors intend to obtain a larger sample size in the future to facilitate surgical planning for lateral orbital wall decompression surgery, enhancing safety while maximizing bone removal in Thai population.

Additional Authors

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