History: A 51-year-old woman underwent a CT scan of the abdomen and pelvis for an evaluation of diarrhea and abdominal pain. An incidental mass was found, and she presented to our institution for further evaluation.
病史：51岁女性，因腹泻、腹痛行腹盆部CT扫描，偶然发现肿物，寻求进一步检查。
An MRI exam of the pelvis was performed. Sagittal T1- and T2-weighted, coronal T1- and T2-weighted, axial fat-saturated T2-weighted, axial and sagittal T1-weighted postcontrast images are shown below. The patient also underwent a PET/CT scan, and a fused PET/CT image also is shown.
行盆腔MR，下方所示图像的序列按顺序为：矢状T1WI及T2WI、冠状T1WI及T2WI、轴位T2WI压脂、轴位及矢状T1WI增强，融合的PET/CT图像如下所示。
Findings
MRI: Deep within the pelvis, there is an 8.0 x 4.5 x 6.5-cm mass involving the pelvic floor musculature with associated encasement of the distal coccyx. The lesion demonstrates intermediate T1 and T2 hyperintensity and contains small foci of T1 hyperintensity internally prior to contrast administration, a finding which may represent hemorrhagic or proteinaceous components. The mass enhances heterogeneously. The fat plane between the mass and distal rectum is intact, and there is no evidence of rectal invasion.
PET/CT: PET/CT demonstrates an FDG-avid, lobulated presacral mass with maximum standard uptake value of 10.1. The mass has a few foci of photopenia centrally, which may represent necrosis versus mass heterogeneity.
影像表现：
MRI：盆腔深部见一大小约 8.0 x 4.5 x 6.5cm肿物，累及盆底肌肉及尾骨远端。病变呈T1等及T2高信号，平扫T1WI肿瘤内可见局灶性高信号，可能提示出血或蛋白成分。肿瘤不均质强化。肿物与直肠远段之间的脂肪层完整，无直肠受侵。
PET/CT：骶前分叶状肿物，FDG明显摄取，最大SUV为10.1。肿块中心局限性低摄取，提示肿瘤不均质，局部坏死。
Differential diagnosis
Sacrococcygeal chordoma
Chondrosarcoma
Giant cell tumor
Metastases
Plasmacytoma
Lymphoma
Sacrococcygeal teratoma
Diagnosis: Sacrococcygeal chordoma
鉴别诊断：
骶尾部脊索瘤
软骨肉瘤
骨巨细胞瘤
转移瘤
浆细胞瘤
淋巴瘤
骶尾部畸胎瘤
最后诊断：骶尾部脊索瘤
The patient underwent wide resection with negative margins. Postoperative T1-weighted fat-saturated postcontrast and T2-weighted axial images are shown below. 肿瘤切除（边缘阴性）术后，T1WI-FS增强及T2WI轴位图像如下所示。
Findings
Postsurgical changes of presacral chordoma resection are seen without findings suspicious for residual, recurrent, or metastatic chordoma in the pelvis. Enhancing tissue in the surgical bed is likely postsurgical. A small fluid collection is seen within the resection cavity, likely a postoperative seroma.
影像表现：
骶前脊索瘤切除术后改变，盆腔内无残留、复发或转移表现。术区强化组织为术后改变，局部可见少量液体积聚，可能为术后血清肿。
Sacral chordoma
Pathophysiology 病理生理
Chordomas arise from notochord remnants. Chordomas are typically slow-growing.脊索瘤起源于脊索残余物，通常生长缓慢。
Notochord arises in the third gestational week and disappears by the seventh week. 脊索在第三周出现并在第七周消失。
Notochord cells occur in the axial skeleton from the coccyx to dorsum sellae. 脊索细胞存在于从尾骨到鞍背的轴向骨架中。
The notochord is composed of cells derived from the mesoderm. 脊索由来自中胚层的细胞组成。
Location: sacrococcygeal (50%), sphenooccipital (35%), mobile spine (15%). 发病部位：骶尾部（50%），蝶枕部（35%），可活动脊柱（15%）。
Since chordomas typically arise in bone, they are mostly extradural. 由于脊索瘤通常出现在骨骼中，因此它们主要是硬膜外的。
Distant metastases are seen in 5% to 40% of cases, most commonly to the lungs, liver, lymph nodes, and bone. 在5％至40％的病例中可发生远处转移，最常见于肺，肝，淋巴结和骨。
Genetic associations with losses on chromosomal arms 3p (50%) and 1p (44%) and gains on 7q (69%), 20 (50%), 5q (38%), and 12q (38%). 与遗传相关：染色体组3p（50％）和1p（44％）的缺失，7q（69％），20（50％），5q（38％）和12q（38％）的获得。
They are staged using the Enneking system for musculoskeletal sarcomas, which assesses anatomic setting, grade of biologic aggressiveness, and presence of metastasis. 使用Enneking系统对肌骨的肉瘤进行分期，评估解剖环境，生物侵袭性等级和转移情况。
Prognosis is typically poor: 预后一般较差
Local recurrence is common and seen in up to 90% of cases. 局部复发很常见，在高达90％的病例中可以见到。
Distant metastases are seen in 5% of cases, most commonly to the lungs and bone. 5％的病例出现远处转移，最常见于肺和骨。
The five-year survival rate is 67% to 84%. 五年生存率为67%-84%。
The 10-year survival rate is 40%. 十年生存率为40%。
Epidemiology 流行病学
Sacral chordomas are in children and in African Americans, and common in Caucasians. 骶骨脊索瘤多见于儿童和非裔美国人，在高加索人中很常见。
Peak incidence is in the fifth to sixth decades. 发病高峰年龄为50-60多岁。
Incidence is 0.08 in 100,000 individuals. 发病率为10万分之0.08。
It is the most common primary nonlymphoproliferative malignancy of the spine. 是脊柱最常见的原发性非淋巴组织增生性恶性肿瘤。
More common in males, with a male-to-female ratio of 2:1. 多见于男性，男女比例为2：1。
Chordomas account for 2% to 4% of primary malignant bone neoplasms. 脊索瘤占原发性恶性骨肿瘤的2％-4％。
Clinical presentation 临床表现
Patients with sacral chordomas may present with weakness, sacral mass, altered sacrogluteal sensation, and/or bowel, bladder, or sexual dysfunction. 骶骨脊索瘤患者可表现为虚弱，骶骨肿块，骶髂关节感觉异常，和/或肠，膀胱或性功能障碍。
Symptoms are typically longstanding (four to 24 months). 症状通常长期存在（4至24个月）。
Imaging features 影像表现
Radiograph： 平片
Appears as a heterogeneous, destructive mass of vertebral body. 椎体不均质肿物并骨质破坏。
May extend into the disk space or involve two or more adjacent vertebrae. 可累及椎间盘或两个以上邻近椎体。
May result in neural foraminal enlargement. 可导致神经孔道扩大。
Can see osseous sclerosis in up to 60% of cases. Rarely, will see solitary sclerotic “ivory” vertebra. 高达60%的病例可见骨质硬化表现，很少表现为单发硬化的象牙质椎体。
CT：
Noncontrast-enhanced CT：CT平扫
Appears as a destructive, lytic lesion. 囊性骨质破坏肿物。
An associated soft-tissue mass is often seen that is usually disproportionately large relative to osseous destruction. 通常可见相应的软组织肿块，肿块之大与骨质破坏不成比例。
Amorphous intratumoral calcifications may be seen. 可见不成型的瘤内钙化。
Contrast-enhanced CT： CT增强
Will have mild to moderate enhancement. 表现为轻至中度强化。
Inhomogeneous areas (cystic necrosis, hemorrhage) may be seen. 密度不均，可见囊变坏死及出血。
MRI:
T1-weighted imaging: T1WI
Heterogeneous hypointense to isointense (compared with marrow) 不均匀低至等信号（与骨髓相比）
Hyperintense to cerebrospinal fluid (CSF), intervertebral disks 信号高于脑脊液和椎间盘
May have low signal septations (fibrous) 可见低信号分隔（纤维）
T2-weighted imaging： T2WI
Hyperintense to CSF, intervertebral discs 呈接近脑脊液及椎间盘的高信号
May have low signal septations (fibrous) 可见低信号分隔（纤维）
Contrast-enhanced T1-weighted imaging: Variable enhancement will be seen. 增强扫描：不同程度的强化
Myelography: Seen as a large, extradural mass. 脊髓造影：可见较大的硬膜外肿物。
Bone scan: Will show normal or decreased uptake. 骨扫描：正常或低摄取。
Treatment 治疗
Treatment typically consists of en bloc resection with adjuvant chemoradiation. 治疗通常包括采用辅助化放疗的整块切除术。
Percutaneous radiofrequency ablation is sometimes used as an adjunct. 经皮射频消融有时作为辅助手段。
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