Computed tomography evaluation of the morphometry and variations of the infraorbital canal relating to endoscopic surgery

Abstract Introduction: The course of the infraorbital canal may leave the infraorbital nerve susceptible to injury during reconstructive and endoscopic surgery, particularly when surgically manipulating the roof of the maxillary sinus. Objective: We investigated both the morphometry and variations of the infraorbital canal with the aim to show the relationship between them relative to endoscopic approaches. Methods: This retrospective study was performed on paranasal multidetector computed tomography images of 200 patients. Results: The infraorbital canal corpus types were categorized as Type 1: within the maxillary bony roof (55.3%), Type 2: partially protruding into maxillary sinus (26.7%), Type 3: within the maxillary sinus (9.5%), Type 4: located anatomically at the outer limit of the zygomatic recess of the maxillary bone (8.5%). The internal angulation and the length of the infraorbital canal, the infraorbital foramen entry angles and the distances related to the infraorbital foramen localization were measured and their relationships with the infraorbital canal variations were analyzed. We reported that the internal angulations in both sagittal and axial sections were mostly found in infraorbital canal Type 1 and 4 (69.2%, 64.7%) but, there were commonly no angulation in Type 3 (68.4%) (p < 0.001). The length of the infraorbital canal and the distances from the infraorbital foramen to the infraorbital rim and piriform aperture was measured as the longest in Type 3 and the smallest in Type 1 (p < 0.001). The sagittal infraorbital foramen entry angles were detected significantly smaller in Type 3 and larger in Type 1 than that in other types (p = 0.003). The maxillary sinus septa and the Haller cell were observed in 28% and 16% of the images, respectively. Conclusion: Precise knowledge of the infraorbital canal corpus types and relationship with the morphometry allow surgeons to choose an appropriate surgical approach to avoid iatrogenic infraorbital nerve injury.

摘要 引言：眶下管（infraorbital canal）的走行路径可使眶下神经（infraorbital nerve）在重建手术与内镜手术中易遭受损伤，尤其当术者对上颌窦（maxillary sinus）顶壁进行外科操作时。
研究目的：本研究旨在探究眶下管的形态计量学特征与解剖变异情况，以明确其与内镜手术入路之间的关联。
研究方法：本回顾性研究对200例患者的鼻旁窦多层探测器计算机断层成像（multidetector computed tomography）图像进行了分析。
研究结果：眶下管分型如下：1型：走行于上颌骨骨性顶壁内（55.3%）；2型：部分突入上颌窦腔内（26.7%）；3型：完全走行于上颌窦腔内（9.5%）；4型：解剖位置位于上颌骨颧隐窝的外侧缘（8.5%）。本研究测量了眶下管的内部夹角、管长，眶下孔（infraorbital foramen）入口角度以及与眶下孔定位相关的各项距离，并分析了上述参数与眶下管变异分型之间的相关性。结果显示，矢状位与轴位图像上的内部夹角多见于1型和4型眶下管（占比分别为69.2%、64.7%），而3型眶下管大多无夹角（68.4%，p<0.001）。眶下管长度、眶下孔至眶下缘及梨状孔（piriform aperture）的距离在3型中最长，1型中最短（p<0.001）。矢状位眶下孔入口角度在3型中显著小于其他分型，1型则显著大于其他分型（p=0.003）。本研究纳入的图像中，28%可见上颌窦间隔，16%可见哈勒气房（Haller cell）。
研究结论：精准掌握眶下管的分型特征及其与形态计量学参数的关联，可帮助外科医师选择合适的手术入路，从而避免医源性眶下神经损伤。