健康人眼外肌厚度及宽度的MRI研究

MRI study of the thickness and width of the extraocular muscles in normal subjects

目的 采用MRI技术研究健康人各条眼外肌的厚度及宽度.方法 横断面研究.健康受试者68例,男女各34例,年龄2.0～50.0岁,平均（21.2±2.1）岁.眼眶部自旋回波序列T2WI冠状及垂直视神经的斜冠状扫描,层厚1.5 mm.于斜冠状面上眼外肌最大径线层面测量各条眼外肌的厚度及宽度,内、外直肌的垂直径代表其宽度,水平径代表其厚度,而上、下直肌的垂直径代表其厚度,水平径代表其宽度.垂直径测量肌腹最上缘到最下缘之间的距离,水平径测量肌腹最内缘到最外缘的距离.采用独立样本t检验比较左右两侧眼外肌径线值.以每位受试者上斜肌的径线值做一内参考,分别得出内、外、上、下直肌的径线值与上斜肌径线值的比值,比较同一层面上几条直肌厚度和宽度的大小关系.结果 健康人两侧眼外肌对称,左右两侧内直肌、外直肌、下直肌、上直肌、上斜肌厚度及宽度比较差异无统计学意义（t值分别为0.043,0.025,0.043,0.032,0.001,0.601,0.667,0.021,0.032,0.005,均P值＞0.05）.内直肌、外直肌、上直肌、下直肌厚度与上斜肌厚度比值分别为1.15±0.14,1.04±0.14,1.07±0.19,1.39±0.22,下直肌厚度＞内直肌厚度＞上直肌厚度＞外直肌厚度,且91％（62/68）上直肌厚度和外直肌厚度接近;内直肌、外直肌、上直肌、下直肌宽度与上斜肌宽度比值分别为1.71±0.27,2.07±0.28,1.62±0.29,1.50±0.21,外直肌宽度＞内直肌宽度＞上直肌宽度＞下直肌宽度.结论 各条眼外肌的厚度及宽度有一定规律,眼外肌MRI检查应同时进行冠状面及斜冠状面扫描,分别利用冠状面上双侧眼外肌对称性及斜冠状面上眼外肌粗细规律来判断眼外肌大小是否正常.

Objective To study the thickness and width of extraocular muscles by high-resolution magnetic resonance imaging （MRI）.Methods Cross-sectional study.Sixty eight normal subjects between 2.0 and 50.0 years of age,mean age was （21.2±2.1） （SD） years old,male 34,female 34.Extraocular muscles in the orbits were scanned with SE/T2WI coronal and oblique-coronal planes perpendicular to optic nerve,and within 1.5 mm thick planes.The thickness and width of the extraocular muscles in the maximum planes were measured in 68 normal subjects on oblique-coronal planes MR images.The vertical diameter of the medial rectus muscle and lateral rectus muscle indicated width,horizontal diameter indicated thickness.The vertical diameter of the superior rectus muscle and inferior rectus muscle indicated thickness,horizontal diameter indicated width.Vertical diameter of the muscle belly is from the top edge to the bottom edge,horizontal diameter of the muscle belly is from the innermost to the outermost edge.The differences in diameters of bilateral extraocular muscles were evaluated by the independent sample t statistical test.Superior oblique muscle was considered as a reference in each subject to calculate the ratio of the other rectus muscles and the superior oblique muscle in diameter and to compare the relationship of the extraocular muscles in the same plane.Results The extraocular muscles of normal subjects were symmetrical on the two sides.There were no statistically significant differences between the bilateral extraocular muscles （medial rectus muscle,lateral rectus muscle,inferior rectus muscle and superior rectus muscle） in the thickness and width （t values respectively were 0.043,0.025,0.043,0.032,0.001,0.601,0.667,0.021,0.032,0.005,all P〉0.05）.The ratio of the rectus muscles （medial rectus muscle,lateral rectus muscle,superior rectus muscle,inferior rectus muscle） and the superior oblique muscle in thickness respectively were （1.15±0.14）,（1.04±0.14）,（1.07±0.19）,（1.39±0.22）.The relationship of the thickness of extraocular muscles in the maximum planes were：inferior rectus muscle 〉 medial rectus muscle 〉 superior rectus muscle 〉 lateral rectus muscle,and the thickness of 91% superior rectus muscle was close to lateral rectus muscle.The ratio of the rectus muscles （medial rectus muscle,lateral rectus muscle,superior rectus muscle,inferior rectus muscle） and the superior oblique muscle in width respectively were （1.71 ±0.27）,（2.07±0.28）,（1.62±0.29）,（1.50±0.21）.The relationship of the width of extraocular muscles in the maximum planes were：lateral rectus muscle〉 medial rectus muscle〉 superior rectus muscle〉 inferior rectus muscle.Conclusions The thickness and width of all the extraocular muscles follows a certain rule.Measurements of extraocular muscles using MRI should be done on coronal and oblique-coronal planes MRI scan simultaneously.The sizes of extraocular muscles can be assessed by observing the symmetry of the extraocular muscles on the two sides on coronal plane and the usual rule of extraocular muscles on obliquecoronal plane.