颞下颌关节紊乱病的MRI评估
2020年2月
中华内分泌代谢杂志,第55卷第2期 第139页-第144页
陈志晔,胡敏
颞下颌关节紊乱病(temporomandibular disorders,TMD)好发于中青年,发病高峰为20~40岁,女性多见,可累及10%~15%的成年人,但仅5%的患者进行诊疗[1,2]。TMD常表现为关节盘移位、关节腔积液、髁突退变、翼外肌异常改变等,MRI的软组织分辨率高,且具有多参数、多序列及任意角度成像等特点,是目前临床常用的颞下颌关节影像检查方法之一[3],并且MRI被认为是评估颞下颌关节盘-髁突关系及软组织改变的金标准[4,5,6,7]。
①简单评估,闭口位为倒置"S"型,张口位"领结"型[8,9,10];②关节盘厚度评估(各带最大厚度),前带2 mm,中间带1.1 mm,后带2.8 mm;③常见关节盘形态学包括双凹型、后带增厚型、前带增厚型、拉伸型、折叠型及类圆形(
①按移位层面分为正常上位(关节盘后带后缘位于髁突上方12点的位置,即"盘-突12点")(
由于关节盘为软骨,含水量(即质子含量)较少,因此在所有序列上均为低信号,以质子密度加权成像(proton density weighted imaging,PDWI)最为显著。PDWI图像上关节盘高信号提示退变可能,其中后带表现最为显著(
关节盘严重磨损或损伤可致关节盘穿孔。既往采用磁共振关节腔造影技术进行评估,但该技术为有创检查,目前临床主要采用斜矢状位脂肪抑制T2WI序列进行评估。当所示关节盘内见线样高信号影,并与关节上下腔相通时提示关节盘穿孔。
关节盘粘连是指张口时关节盘不能从关节窝向前移动到关节结节,而是仍保持在关节窝内(
①正常双板区软组织张口位时为呈负压结构,此时软组织膨胀(上板与关节窝相接触,保持一致)改变[13],但发生损伤时负压消失,膨胀改变消失(
通常基于斜矢状位PDWI及横轴位脂肪抑制T2WI进行形态学评估,主要评估内容包括髁突位置、髁突形态、髁突长轴和短轴长度以及髁间角大小[3]。
(1)髁突位置分类:根据髁突前、后斜面与关节窝前、后斜面切线间的距离大小可分为前位、后位及中立位(
(2)髁突形态分类:TMD患者的髁突形态分为卵圆形、扁平形、鸟嘴形(
(3)髁突长轴及短轴:在闭口位横断面T2WI图像髁突最大长轴层面测量髁突内外极最大径(平行于髁突走形方向)长度即为髁突长轴,垂直于长轴的最大径(垂直于髁突走形方向)长度即为髁突短轴(
(4)髁间角:在横轴位T2WI图像上,通过双侧髁突长轴延长线的夹角即为髁间角,髁间角的测量涉及双侧颞下颌关节(
髁突骨质评估常依靠于锥形束CT进行评估,但也可基于MRI斜矢状位PDWI及斜矢状位脂肪抑制T2WI进行评估,评估指标主要包括骨皮质信号是否均匀连续(通常为线样低信号影)、有无骨赘、是否有水肿及囊性变(基于斜矢状位脂肪抑制T2WI序列)以及关节间隙是否变窄(
颞下颌关节符合髁突扁平、骨赘形成、磨损和硬化中的1条即可诊断为骨关节病(
见
颞下颌关节关节腔主要分为关节上腔及关节下腔,关节上腔为1.0~1.2 ml,关节下腔为0.5~0.6 ml[17]。关节腔积液评估主要基于斜矢状位脂肪抑制T2WI序列进行评估。关节腔积液按积液量依次分为4级:即无或少量积液(关节腔内无T2高信号影或沿关节面可见点状或线样T2高信号影)、中度积液、明显积液及大量积液[18]。
翼外肌通常分为上腹及下腹,正常翼外肌通常头部边界清楚,至少斜矢状位两个层面都可以观察到。异常形态改变主要包括:①萎缩,肌肉大小无明显变化而大部分肌肉出现高信号的脂肪替代(斜矢状位PDWI);②肥大,在斜矢状位PDWI图像上肌腹中部体积增大但信号均匀,肌腹中部呈凸形改变;③挛缩,肌肉增大,同时可见纤维化改变,在斜矢状位PDWI上肌腹内可见低信号影(
包括脂肪变性及纤维化,脂肪变性在斜矢状位PDWI表现为高信号影,常合并翼外肌萎缩改变;而纤维化表现为低信号影,常合并挛缩改变(
翼外肌上腹附着于关节盘的形式主要分为3种类型,第1种类型上腹纤维附着于关节盘,下腹附着于髁突(29.6%);第2种类型上腹纤维附着于关节盘和髁突,下腹附着于髁突(40.8%);第3种类型上腹纤维附着于关节盘(29.6%),翼外肌的中间部分纤维(翼外肌上腹与下腹汇合处发出的纤维)及下腹纤维附着于髁突[20,21,22]。对于功能评估可以采用T2成像序列测量翼外肌的T2值进行评估,而对于翼外肌结构评估可以采用扩散张量成像及体积测量[23,24]。在临床上也可采用三维T2WI序列行闭口位及张口位成像,并采用多平面重建技术重建翼外肌上腹,沿翼外肌上腹最大走形方向测量翼外肌上腹长度,评估翼外肌收缩程度。
随着MRI技术的进步及对翼外肌在TMD发病中作用研究的深入,临床医师应重视对翼外肌结构、功能及病变的评估及治疗,综合分析翼外肌肌肉收缩程度和症状及体征有助于了解病情、肌肉收缩状况和肌肉性状。
总之,TMD的MRI评估序列主要包括PDWI及脂肪抑制T2WI,一般需行闭口位及张口位磁共振检查。MRI评估内容主要包括关节盘、髁突、关节腔积液及翼外肌等。部分颞下颌关节健康者也可见一定程度的关节盘移位,但无临床症状、因此对于关节盘移位与TMD的诊断应谨慎,需结合临床进行综合诊断[9,25]。
目前临床上对于TMD的MRI诊断报告尚无统一的规范,推荐使用颞下颌关节的结构化图文报告系统,主要包括数据输入模块和图文报告。数据输入模块主要对关节盘、髁突、关节腔积液及翼外肌的相关评估参数进行量化,具体数据输入可结合影像报告系统进行;各项评估参数输入后自动生成图文报告,并由诊断报告医师采集典型图片,附于报告后。一般选取双侧斜矢状位PDWI闭口及张口位图片各1张。
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