目的：观察中颅窝盖板低位对耳后进路清除上鼓室病变的影响，探讨中颅窝盖板低位的分度标准。方法对87例影像科报告中颅窝盖板低位的慢性化脓性中耳炎患者的 CT 图像进行冠状位重建，沿外耳道上壁最高点作水平切线 L1，自该层面出现上半规管结构的最高点作水平切线 L2，沿该层面的中颅窝盖板最低点作水平切线L3，测量 L1～L2距离 a 和 L1～L3距离 b，计算 b／a 值 r，依据 r 值将中颅窝盖板低位分为正常、轻、中、重及绝对低位，与3位手术医生术前评估及手术记录结果进行比较。结果手术医生根据不同的 r 值，不同观点如下：①当r ＜1／4时，不认同影像科提示的中颅窝盖板低位；②当1／4≤r ＜1／3时，认同中颅窝盖板低位，但手术记录中未提及；③当1／3＜r≤1／2时，清除上鼓室病变时均遇到过磨破中颅窝盖板底壁骨质的病例，手术会因为术中止血而受到影响；④当1／2＜r≤3／4时，术前已明显感觉中颅窝盖板低位，在清除上鼓室病变时仍有保留外耳道后壁完整的病例；⑤当 r ＞3／4时，清除上鼓室病变时非常困难，中颅窝盖板低位导致的耳后进路已不可避免的要磨除外耳道后壁。结论可依据 r 值可将中颅窝盖板低位分无、轻、中、重及绝对低位“5度”，轻度对耳后进路清除上鼓室病变无影响，中度耳后进路清除上鼓室病变存在困难，重度经耳后进路清除上鼓室病变部分需要磨除外耳道后壁，绝对低位时磨除外耳道后壁已不可避免。“,”Objective To observe the effect of high-resolution computed tomography (HRCT)grading of low middle fossa tegmen plate on the elimination of diseased tissue in epitympanum and to investigate the grading standard of low middle fossa tegmen plate.Methods The CT images obtained from 87 chronic otitis media (COM)cases were sub-jected to coronal reconstruction.A horizontal tangent L1 at the highest point along the upper wall of external auditory canal,a horizontal tangent L2 at the highest point of the semicircular canal structure,and a horizontal tangent L3 at the lowest point along the middle fossa tegmen plate were created to measure the distance between L1 and L2,L1 and L3, and to calculate the r value (b/a).The r value was used to divide the low middle fossa tegmen plate into five grades:non-low,mild,moderate,severe,and absolute low.Pre-operative evaluation and postoperative results were compared. Results Surgeons had different opinions on the r value:(1)If r <1 /4,the low middle cranial fossa cover identified by the Radiation Department could not be accepted.(2)If 1 /4 ≤ r <1 /3,the low middle cranial fossa cover identi-fied by the Radiation Department could be accepted,but it was not mentioned in the operation record.(2)If 1 /3