ASOPRSFall Scientific SymposiumSyllabus
172
T19
TheOrbital Strut Revisited: AnatomicDefinition andComputer-Assisted
VolumetricAnalysis of BoneyVolume
Jennifer Lira, CarisaPetris, JoyceKhandji, Alexander Khandji,Michael Kazim. Department of Ophthalmology, ColumbiaUniversity
Medical Center, NewYork-PresbyterianHospital, NewYork, NY, UnitedStates
Introduction:
The portion of the bony orbit known as the inferior-orbital strut (IOS) is of particular interest to orbital surgeons
performing bony decompression.The orbital strut has been previously described as the bony thickening at the junction of the
maxillary and ethmoid bones beginning at the inferior orbital rim, extending to the posterior palatine bone[1]. Using volumetric
software,wewere able to delineate the portion of the orbital strut that is safely removed during boney decompression formaximal
expansion of the orbit.This includes bone between the posterior lacrimal crest to themost posterior ethmoid air cell, anterior to the
palatine bone.
Methods:
A retrospective IRB-approved radiographic study inwhich the IOSwas analyzedwith high resolutionCT scans selected
from over 9000 scans performed at NYPH from 2008-14.All scanswere high resolution and<1.6mm thickness. Scanswere
excluded in patientswith orbital surgery or trauma, craniofacial abnormalities, or orbital tumors.Volumetric analysiswas performed
withVitreaWorkstation™Version6.5.3. byVital Images, Inc.The IOSwas outlined at the junction of themedial and inferior orbital
walls. Outlinesweremade in the coronal viewwhile simultaneously visualizing the points on sagittal, axial, and 3D reconstruction
planes.The junction of the posterior lacrimal crest,maxillary floor, and ethmoid bone served as the anteriormargin.The posterior
marginwas located just anterior to the posterior aspect of the palatine bone.The software yielded volumemeasurements and 3D
reconstructions of the orbital strut.
Results:
Twenty-one scans (41 orbits) were studied to determine variance and power of the available data.The strut was found
to be triangular in shape in coronal views.The anterior-most portionwas easily identified at the junction of the ethmoid andmaxillary
bones just posterior to the nasolacrimal canal.The strut ended posteriorly to the junction of the ethmoid and palatine bones.
The bony strut was thickest anteriorly and posteriorly.Amean IOS volume (mm
3
) of 385.0OD and 405.2OS (SD=131.6OD,
141.7OS) was calculated.
Conclusions:
This study provides radiographic characterization of the dimensions of the orbital strut with emphasis on volumetric
analysis.Although the volume occupied by the IOS as defined is small, and if removed, adds only 1% to the total orbital boney
volume,we believe IOS removal produces amore significant increase in orbital volume as a consequence of the expansion of orbital
soft-tissues beyond the volume occupied by the IOS into the adjacent sinuses after the periorbita is opened.We suggest that the
most posterior ethmoid air cell should be removed in all cases tomaximize volume expansion but does not constitute a portion of the
strut. Conversely, removal of the palatine bone does not significantly increase volume and carries additional operative risk.
References:
Kim JW, et al.The Inferomedial Orbital Strut:AnAnatomic and Radiographic Study.OPRS.2002;18:355-364
DetailedProgram
—Thursday,October 16, 2014
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