Yang Haisong, Yang Lili, Chen Deyu, Wang Xinwei, Lu Xuhua, Yuan Wen
Department of Orthopedics, Changzheng Hospital, No. 415 Fengyang Road, Shanghai, 200003, China.
Eur Spine J. 2015 Aug;24(8):1631-9. doi: 10.1007/s00586-015-3914-1. Epub 2015 Apr 4.
To make a preliminary classification of double-layer sign according to the morphological characteristics of the ossified and central hypodense mass and clarify implications of different patterns of "double-layer sign".
The 268 patients of cervical ossification of the posterior longitudinal ligament (OPLL) who underwent anterior corpectomy were retrospectively analyzed from January 2009 to January 2014. All these patients were performed cervical plain X-rays, CT and MRI. The double-layer sign was observed on axial bone window of CT images. According to the morphological characteristics of the ossified and central hypodense mass, this sign was classified into three types: type A was crescent shape, type B was short-straight shape and type C was long-straight shape. Type A was named when the central hypodense mass traced an arc and the OPLL is much more extensive than the dural ossification (DO). It belonged to type B when the central hypodense mass traced a short-straight line, less than or equal to half of the base width of the vertebrae. The OPLL may be extensive or equal to the DO. Type C was defined when it was more than half of the base width, presenting with a long-straight line and DO is much more extensive than OPLL. Intraoperative findings including dural mater ossification and adhesion, postoperative CSF leakage and outcome were all studied. Two spinal surgeons with rich experiences read the CT images according to this classification method and verified its consistency.
Ninety-two patients were found in association with DO during the anterior decompression procedure, meanwhile the double-layer sign could be seen on axial bone window of CT imaging. In these 92 patients, there were 51 patients presenting with type A, and the ossified mass was completely resected with ossified dura mater reserved. Only two patients presented with dural defect and postoperative CSF leakage. Thirty-five patients was classified as type B, of which six accompanied by CSF leakage. All the other six patients of type C presented with CSF leakage after operation. There was a significant correlation between the occurence of CSF leakage and pattern of double-layer sign, but not gender, age, duration of symptoms, extent of OPLL and occupying rate. The Kappa value between the two surgeons was 0.82, showing a good consistency of the method.
OPLL patients with double-layer sign of type C is almost inevitably followed by CSF leakage after anterior decompression. For type A and B, occurrence of CSF leakage is not as high as we thought before. Pattern of double-layer sign should be a considered factor when anterior or posterior approach is chosen.
根据骨化及中央低密度肿块的形态特征对双层征进行初步分类，并阐明不同模式“双层征”的意义。
回顾性分析2009年1月至2014年1月期间接受前路椎体次全切除术的268例颈椎后纵韧带骨化（OPLL）患者。所有患者均行颈椎X线平片、CT及MRI检查。在CT图像的轴位骨窗上观察双层征。根据骨化及中央低密度肿块的形态特征，将该征象分为三型：A型为新月形，B型为短直线形，C型为长直线形。当中央低密度肿块呈弧形，且OPLL比硬脊膜骨化（DO）广泛得多时为A型。当中央低密度肿块呈短直线形，长度小于或等于椎体基底宽度的一半时为B型。此时OPLL可能广泛或与DO相等。当中央低密度肿块长度超过椎体基底宽度的一半，呈长直线形，且DO比OPLL广泛得多时为C型。研究术中所见包括硬脊膜骨化及粘连、术后脑脊液漏及预后情况。两位经验丰富的脊柱外科医生根据该分类方法阅读CT图像并验证其一致性。
92例患者在前路减压手术中发现合并DO，同时在CT图像的轴位骨窗上可见双层征。在这92例患者中，51例为A型，骨化肿块被完全切除，保留骨化的硬脊膜。仅2例出现硬脊膜缺损及术后脑脊液漏。35例为B型，其中6例伴有脑脊液漏。C型的其余6例患者术后均出现脑脊液漏。脑脊液漏的发生与双层征模式之间存在显著相关性，但与性别、年龄、症状持续时间、OPLL范围及占位率无关。两位外科医生之间的Kappa值为0.82，表明该方法具有良好的一致性。
C型双层征的OPLL患者前路减压术后几乎不可避免地会出现脑脊液漏。对于A型和B型，脑脊液漏的发生率并不像我们之前认为的那么高。在选择前路或后路手术时，双层征模式应作为一个考虑因素。
