泪囊-鼻泪管移行部压迹的MRI研究

MRI Features of the Newly Identified Indentation of the Lacrimal Sac and Nasolacrimal Duct( LS-NLD) Junction

目的探讨正常泪囊-鼻泪管移行部压迹的MRI表现和生理学意义。方法对52名104侧正常泪囊鼻泪管行MRI扫描,扫描范围包括全部泪道系统。扫描方位有轴面、冠状面和斜冠状面;轴面平行于眼眶下缘;冠状面平行于泪囊鼻泪管的冠状面,主要依赖泪囊鼻泪管的连续轴面图定位;斜冠状面垂直于移行部压迹的弦,主要依赖移行部的连续轴面图定位。扫描序列为常规T_2WI、增强3D FIESTA-C、脂肪抑制增强T_1WI和脂肪抑制重T_2WI。用无间隔、连续最薄层厚。结果正常泪囊鼻泪管104侧,每侧泪囊-鼻泪管移行部的后外侧壁都存在局部管壁向腔内的凹陷,即有压迹形成,长约4 mm,深度不一致;压迹处横断面和管腔呈现半月形,局部管腔狭窄。在17侧增强扫描和40侧平扫中发现移行部与眶脂体间有小血管相连。泪囊鼻泪管的管腔狭小,泪囊中的泪液多于鼻泪管;管腔的形态和大小(关闭与开放)在不同的平面而不同;28.8%(30/104)的泪囊、64.4%(67/104)的移行部和22.1%(23/104)的鼻泪管管腔处于关闭状态。结论正常泪囊-鼻泪管移行部后外侧的压迹是固有的解剖结构,是该处生理性管腔狭窄的根本原因;在正常泪液引流过程中,压迹结构起重要作用。

Objective To investigate the presence and possible physiological function of the indentation of lacrimal sac（ LS）-nasolacrimal duct（ NLD） junction. Methods The normal human LS-NLD was imaged in three different planes by conventional T2 WI,contrast-enhanced 3D FIESTA-C,contrast-enhanced T1 WI and heavily T2 WI pulse sequences with the thinnest slice thickness and consecutive sections（ no spacing）. The axial scanning plane was parallel to the orbital floors.The coronal scanning protocol was drafted mainly on consecutive axial images of LS-NLD and its plane was parallel to LSNLD＇s coronal plane. The oblique-coronal scanning protocol was set mainly on consecutive axial images of the junction andits plane was perpendicular to the chord of the indentation. The whole systems of the lacrimal drainage ducts were included in the imaging field. Results A total of 104 sides of normal LS-NLD（ 52 subjects） were analyzed by the MRI scanning.In all LS-NLDs,an indentation located at the posterior-lateral side wall of the junction of LS-NLD was discovered. The indentation was about 4 mm long with variable depth. On cross sectional view,the junction lumen showed a narrow crescent shape. Small blood vessels between the junction and the adipose body of orbit were revealed by plain scanning（ in 40 junctions） and contrast-enhanced scanning（ in 17 junctions）. The lumen of LS-NLD was narrow,small and irregular. More tear was present in LS than in NLD. The shape and size（ open or closed） of the lumens varied at different sites of the LSNLD. In 28. 8%（ 30 /104） of LS,64. 4%（ 67 /104） of the junctions and 22. 1%（ 23 /104） of NLD,lumens were closed.Conclusion The indentation of LS-NLD junction is an inherent anatomic apparatus neglected by anatomists for a long time,and it is a main contributing factor for the physiological stricture of the junctional lumen. It could play a regulating role on the tear outflow in LS-NLD.