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脊柱转移瘤(metastatic spine tumors, MST)可继发于体内任何恶性肿瘤, 60%以上来源于肺癌、乳腺癌和前列腺癌等。近年的研究表明, 恶性肿瘤的MST发生率约为10%, 发生器官转移并导致脊髓受压者占5%~20%[1-3]。由于脊柱各部分尤其是腰段多富含红骨髓成分, 其静脉系统(即Baston静脉丛)无瓣膜结构, 且邻近血管丰富, 因此, 有利于肿瘤细胞滞留并进一步发展为MST[4], 经椎静脉进入的瘤栓常首先停留于椎体后部, 引起局部骨质破坏, 然后进一步侵及椎弓、横突、椎板、棘突等; 此外还通过直接扩散, 种植于椎体毛细血管网内; 椎间盘因缺乏血运故不易受累。MST的发生部位中, 颈椎占28%;颈胸椎同时受累者占45%, 腰椎占27%。80%的病变累及椎体, 其次是脊柱后方结构[3]。
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为了达到对MST早期诊断、早期治疗的目的, 临床中广泛采用放射性核素骨平面显像, 它能对整个骨骼进行扫描。骨显像依靠成骨反应(即骨沉积)来发现转移灶, 常用的示踪剂为99Tcm-亚甲基二膦酸盐, 是功能代谢显像。由于肿瘤部位血流丰富, 代谢旺盛, 可浓聚较多的示踪剂而呈现异常的放射性浓聚区, 称为“热区”显像; 另外, 由于肿瘤的高度侵袭, 致使病灶局部血运循环障碍, 少数骨转移灶呈现放射性缺损区, 称“冷区”显像。其可在临床症状出现前2~6个月, 甚至12个月以前发现肿瘤骨转移灶[12-13]。
由于平面显像清晰度等方面的限制, 而脊柱结构比较复杂, 因此其往往不能清晰显示解剖结构, 致使图像分析困难; 并且, 常规核素骨平面显像虽然灵敏度较高, 但特异度不高, 脊柱的骨折、退行性病变以及良性病变也都呈阳性结果; 而椎旁肿瘤通过神经孔进入硬膜外间隙而导致背痛和进行性神经症状者行核素骨平面显像常不能发现异常。另外, 核素骨平面显像无法观察转移瘤对椎体的破坏程度, 解剖定位不准确[14]。
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SPECT可对全身骨骼进行横断、冠状和矢状位等不同角度的断层显像。因此, 骨SPECT能弥补骨平面显像的不足, 它在MST的诊断中的作用主要有以下几个方面:
(1) 骨SPECT较平面显像的灵敏度更高, 成像更清晰。Reinartz等[15]对93例腰痛患者(其中54例患恶性肿瘤)的骨平面和SPECT结果进行比较, 结果显示, 平面显像探测脊柱病灶的灵敏度 > 70%, 而骨SPECT可达90%以上。
(2) 骨SPECT可提示病灶累及的解剖结构或分布形态。Even-Spair等[16]对233例腰痛患者(其中75例患恶性肿瘤)的脊柱SPECT图像进行统计学分析, 结果表明, 仅累及附件结构的病灶都为良性; 仅累及椎体的病灶, 无论其分布形式是周边型还是弥漫型, 大部分为良性(散在周边型占96%, 弥漫型占87%); 同时累及椎体和椎弓根的病灶, 恶性病变的概率达83%;同时累及椎体及附件而不累及椎弓根的病灶, 良性病变的概率为93%。
(3) 骨SPECT可定量分析放射性浓聚灶。Buell等[17]提出, 利用骨SPECT定量分析病灶的放射性摄取水平与周围正常骨组织的比值, 可为病灶良恶性的鉴别提供信息。
(4) 骨SPECT-CT融合显像的诊断应用。骨SPECT-CT融合显像不仅具有SPECT灵敏度较高的优点, 可将某些CT上无异常表现的病灶筛选出来, 还具有利用其CT图像能分辨骨皮质或骨髓质病变的优点, 对骨SPECT所示仅累及椎体的病灶作出更准确的良、恶性鉴别诊断。Utsunomiya等[18]研究提出, 骨SPECT-CT可提高对MST诊断的灵敏度和特异度, 并为临床规范应用提供了依据。Ro mer等[19]研究显示, SPECT-CT对可疑脊柱浓聚灶诊断为骨转移性肿瘤的灵敏度为83.87%, 特异度为88.41%, 准确率为87%, 阳性预测值为76.47%。
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PET-CT是近年来已逐渐应用于临床肿瘤学的一种融合显像技术, 它既可以提供高分辨率、高信噪比的解剖图像, 也能提供肿瘤功能以及代谢方面的信息, 一次检查即可获得功能与解剖两方面的信息, 实现了功能与解剖图像的同机融合。由于脊椎在人体平卧时无位移, 18F-FDG PET-CT可以准确确定脊椎异常摄取18F-FDG的部位, 弥补了18F-FDG PET定位诊断的不足, 有利于椎体骨病变的鉴别诊断; 同时提供了病变的功能代谢信息, 为病变的早期诊断提供了依据; 可以准确做出肿瘤分期, 从而选择正确的治疗方案。椎体病理性压缩性骨折等是临床需要早期确诊、积极处理的骨恶性病变[20-21], Dehdashti等[22]使用18F-FDG PET鉴别骨质疏松性压缩性骨折和病理性压缩性骨折, 并判断治疗后的肿瘤存活情况: 症状出现以后, 超过3 d的骨质疏松性压缩性骨折呈低代谢状态, 其标准化摄取值(standardized uptake value, SUV) < 3, 而肿瘤的SUV一般为 > 5。另外, 18F-FDG PET还有助于引导对代谢活性高的肿瘤部位进行活检。Duarte等[23]的研究表明, 18F-FDG PET-CT能较好的鉴别骨质疏松与恶性病变导致的压缩性骨折, 骨质疏松(包括临床前骨质疏松)导致的畸形椎体压缩性骨折应无病理性18F-FDG高摄取, 其SUV为1.1~2.4, 而肿瘤导致的压缩性骨折的SUV为3.8~9.8。
总之, 放射性核素骨显像具有很高的灵敏度, 可以显示全身骨骼的病理改变, 能反映各个局部骨骼的血液供应和代谢变化, 并且可以显示脊柱的形态学改变。目前, 临床已将核素骨显像作为肿瘤诊疗的主要评价手段。
放射性核素骨显像在脊柱转移瘤诊断中的价值
Evaluate the diagnostic value of radionuclide bone imaging of metastatic spine tumors
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摘要: 脊柱转移瘤(MST)可发生于原发恶性肿瘤临床的各个阶段，传统X线片发现时多为中晚期病变；CT容易漏诊，不能直接显示脊髓的异常；MRI耗时长，病痛的患者不易配合，影响图像的质量。常规骨扫描能够对整个骨骼进行扫描，但特异性不高。核素SPECT骨显像可提高对MST诊断的敏感性和特异性，提示病灶累及的解剖结构或分布形态，并能定量分析放射性浓聚灶；PET-CT能够清楚鉴别脊柱病变，实现早期诊断，并可早期评估化疗或放疗疗效。该文进一步阐述核素骨显像在MST早期诊断中的价值。Abstract: Metastatic spine tumors(MST)can occur in many primary malignant tumors, but X-ray cannot find early metastatic disease; CT scans can not directly show abnormity of the spinal marrow; MRI need a long time, patients with spinal tumors can hardly to be suffered which will affect image quality.Conventional bone scan has the ability to scan the entire skeleton, but the specificity is not high.However, the sensitivity and specificity can be improved about the diagnosis of MST by bone SPECT imaging, the distribution of the anatomical structure or morphology of the metastatic spinal tumors can be clearly displayed.PET-CT could detect the metastases of spine and other parts of the body sensitively and accurately, primary tumors that were unknown before examination could be found at the same time.This paper describes the diagnostic value of radionuclide bone scintigraphy of MST.
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Key words:
- Spinal neoplasms /
- Bone /
- Radionuclide imaging
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