This is a radiological study of the volume of the sphenoid trigone in normal subjects. The authors were interested to see how much volume could be gained by removal of the trigone during an orbital decompression for thyroid eye disease. Specifically, they were looking at the natural anatomical variation and differences due to gender or race. CT scans from 120 normal subjects were found with 40 each from three racial groups; Asian, black/African American and white. Each group had 20 males and females, all aged 30-60. Both orbits of each subject were analysed to measure the volume of the trigone by measuring the area of the trigone in every 2mm axial slice between the superior and inferior orbital fissures. These areas were then summed and multiplied by two (the slice thickness) to give the volume. The mean volume overall was 1.53 cm³ with a range of 0.2 to 4.4 cm³. Male subjects had a significantly larger mean volume than females but there was no significant difference between races. Interestingly, right trigones were significantly smaller than left. An important finding emphasised by the authors is the very wide natural range in volumes, with some subjects having 10 times the volume of others within the same sub-group. Furthermore there can even be large differences between the two orbits in the same subject, with the trigone on one side having twice the volume of the other. Understanding this extreme variability is important in planning decompression surgery and the paper makes this point clearly with good supporting data.

CT-based measurements of the sphenoid trigone in different sex and race.
Lefebvre DR, Yoon MK.
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James Hsuan

Aintree University Hospital, Liverpool, UK.

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