Radiologic Findings and Differential Diagnosis of Chordomas in the Spine

Chordoma of the spine generally presents with back pain, whereas neurologic
symptoms and other manifestations of mass effect, such as tracheal or esophageal compression, are less frequent. 1 Grossly, chordoma is a soft, lobulated, irregularly
circumscribed, gray to white lesion with a pseudocapsule and a glistening myxoid cut surface 2,​3,​4 ( ▶ Fig. 10.1, ▶ Fig. 10.2). Most chordomas penetrate beyond the vertebral body, and the encapsulation is generally incomplete, with microscopic tumor rests identified at a distance from the main tumor. 5 The lesions frequently contain regions of hemorrhage, cystic change, and calcification. 3,​5 Histologically, chordoma is composed of cords and islands of tumor cells within a mucinous or myxoid stroma separated by fibrous septa. 3,​5 The tumor cells include elongated epithelial cells and the characteristic physaliphorous cells, which contain small, dark, and round or ovoid nuclei and abundant multivacuolated cytoplasm. 3 The definitive notochord forms during the third week of embryonic development, underlies the neural tube, and is a signaling center for inducing axial skeletal development and segregation of the brain. 6 Typically, the notochord regresses entirely in the region of the vertebral bodies, but persists and enlarges in the region of the intervertebral discs and contributes to the nucleus pulposus. 6 Persistent notochord tissue in adults was first described in 1856–1857 by Luschka and Virchow, 6 and a persistent notochord canal was described in 1891 by Musgrove. 7 A persistent notochord can be identified on computed tomography (CT) as a central canal with a sclerotic rim within a vertebral body. 8 Magnetic resonance imaging (MRI) demonstrates a vertical canal in the anterior aspect of the vertebral bodies with slightly lower T1 and T2 signals as compared with normal vertebral bone marrow, surrounding low signal on all sequences consistent with rim sclerosis seen on CT, and a rounded T2-hyperintense nonenhancing region in the center of the canal. 9 Most studies report that persistent notochords span only one or two levels, but a span of six levels has also been reported. 9 There have been no reports of chordoma arising from the nucleus pulposus, 10 and it is theorized that all chordomas arise from persistent embryonic notochord rests. 11 These clinical, anatomical, gross, and histologic features of chordoma correlate nicely with the associated radiographic and MRI features. Knowledge of these features and properly including chordoma on the imaging differential can be essential to definitive diagnosis: when physaliphorous cells are not obvious due to dedifferentiation or sampling, the gross pathology and histology can mimic metastatic adenocarcinoma, chondroma, chondrosarcoma, and melanoma. 3 In these instances, definitive diagnosis can often be made by the pathologist by considering imaging findings in conjunction with special stains and electron micrography features. 3



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Fig. 10.1 A 64-year-old female with sacral chordoma. Anteroposterior lumbosacral radiography demonstrates slight rarefaction of the distal sacrum, which is not so easy to depict (a). Axial CT through the distal sacrum (b) and sagittal reformatted CT image (c) clearly show destruction of the sacrum with extensive heterogeneous soft tissue component extending to not only the anterior and posterior of the sacrum, but also into the spinal canal. There is moderate mineralization within the mass. Sagittal T1-weighted MRI image (d) reveals lobulated isointense soft tissue mass that contains hyperintense foci compatible with mucinous materials. Corresponding T2-weighted image (e) depicts hyperintense lobulated mass containing hypointense thin septations. Axial T1-weighted image (f) through the distal sacrum after gadolinium administration demonstrates mild heterogenous enhancement.



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Fig. 10.2 A 31-year-old male with sacral chordoma. (a) Sagittal T1-weighted image demonstrates S3–S5 involvement with presacral isointense soft tissue mass. There is also soft tissue mass within the sacral spinal canal extending to S1 with remodeling of the sacral canal. Corresponding sagittal T2-weighted (b) and short-tau inversion recovery (STIR) (c) images show hyperintense sacral mass with hypointense septations. Borders of the bone involvement and soft tissue mass are best seen on T1-weighted image and STIR or T2-weighted image with fat saturation. Axial fat-saturated T2-weighted image (d) and corresponding T1-weighted image (e) demonstrate lateral extension of the mass containing mucinous or hemorrhagic foci. There is slight enhancement after gadolinium administration on T1-weighted image (f).


10.2 Typical Anatomical Location


A large literature review in 1960 noted a chordoma distribution of 44% intracranial,
42% sacrococcygeal, and 14% in the mobile cervicothoracolumbar spine. 12 Although much of the literature to date references that incidence, a more recent study of over 20 years of the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program data reveals a distribution of approximately 33% in each of these locations. 13 Fitting with the expected location of remnant notochord tissue, spine lesions are generally located in the vertebral body as opposed to the posterior elements, and although up to 66% in one study involved the posterior elements, they also always involved the vertebral body. 1,​14


10.3 CT Features


Spinal chordoma demonstrates vertebral body or sacral destruction with an associated soft tissue mass 1,​2,​4,​12,​15,​16 ( ▶ Fig. 10.1 a–c). The soft tissue lesion is generally mostly anterior or lateral to the mobile spine 2,​4 and mostly anterior in the sacrum, 2 but epidural extension is also present in 60 to 100% of lesions 4,​16 ( ▶ Fig. 10.3, ▶ Fig. 10.4). Multiple vertebral bodies and the intervertebral discs are often involved. 1,​2,​17 Most series suggest that slightly over half of chordomas are predominantly sclerotic with mixed lytic and sclerotic features, whereas slightly less than half are purely lytic. Other series demonstrate a lytic predominance, with one series including no sclerotic lesions. Sclerosis is often present primarily along only the periphery of the lesion, and one report suggests that sclerosis is more commonly seen in the mobile spine than in the sacrococcygeal region. 1 The soft tissue component of the lesion may be relatively homogeneous or may include calcifications or regions of low attenuation ( ▶ Fig. 10.5). Calcifications within the soft tissue component are seen in 15 to 44% of cases. 2,​4,​16 Regions of hypodensity may also be seen and likely correlate with cystic degeneration. 2,​4



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Fig. 10.3 An 88-year-old female with biopsy-proven T9 chordoma. Axial CT images in bone (a) and soft tissue (b) windows and T2-weighted MRI image (c) demonstrate a vertebral body lytic lesion (black arrows) with spinal canal and paraspinal soft tissue components. Sagittal T1-weighted (d), T2 STIR (e), and T1 postcontrast (f) images demonstrate a T1-hypointense, STIR heterogeneously hyperintense, heterogeneously mildly enhancing lesion (black arrows) extending into the spinal canal resulting in posterior cord displacement (white arrow) and cord compression, vertebral body compression, and extension across and likely involvement of the adjacent intervertebral discs and T10 vertebral body (black arrows with white outlines).



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Fig. 10.4 A 61-year-old male with biopsy-proven L2 chordoma. Axial CT images in bone (a) and soft tissue (b) windows and T2-weighted MR image (c) demonstrate a vertebral body lytic lesion (black arrows) with extension into the spinal canal and flattening of the thecal sac (white arrow) with preservation of the pedicles. Sagittal T1-weighted (d), STIR (e), and T1 postcontrast (f) images demonstrate a T1-hypointense, STIR-hyperintense, heterogeneously enhancing lesion (black arrows) extending into the spinal canal.



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Fig. 10.5 An 18-year-old male with cervical chordoma at C1. Axial CT image (a) through C1 demonstrates an expansile lytic mass with some mineralization within it on the right massa. Axial T2-weighted image at the same level demonstrates hyperintense lesion with extensive septations (b). Right parasagittal T1-weighted (c) and T2 STIR (d) images show heterogeneous mass.


10.4 MRI Features


Correlating with the extensive intracellular vacuoles and extracellular mucinous or myxoid stroma seen on histology, T2 signal is almost always high, with a single reported case of intermediate T2 signal. 18,​19,​20,​21 Foci of low T2 signal in one report can most likely be attributed to foci of stromal calcification or hemorrhage. T1 signal is often somewhat heterogeneous but is typically isointense or hypointense to muscle. 18,​19,​20,​21 T1-weighted images may show low signal masses with foci of high signal intensity due to hemorrhage or mucinous material in some cases. The enhancement pattern varies, ranging from none 19 to mild heterogeneous 15 to strong. 18 After contrast administration, using fat saturation techniques may help determine the degree of enhancement. Septations, as seen on pathology, are often seen and are low signal on all sequences. 18,​19,​20,​21 Low-signal septations are usually enhanced after gadolinium administration ( ▶ Fig. 10.6). Although septations are a characteristic finding of chordoma, they are not always seen ( ▶ Fig. 10.7). Soft tissue extension is best seen with MRI. Presacral soft tissue component is a frequent finding. However, posterior extension with involvement of the gluteal muscles is not rare. There are no reports of using advanced imaging techniques in the diagnosis of the spinal chordoma in the literature except diffusion-weighted imaging (DWI). Due to the rich extracellular component of chordoma, it almost always demonstrates mild to moderate increased diffusivity.



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Fig. 10.6 A 51-year-old male with biopsy-proven sacrococcygeal chordoma possibly arising from the lower sacrum, an obliterated coccygeal body, or a midline notochordal remnant rest inferior to the coccyx. Axial CT images at the level of the (a) distal sacrum and (b) ischial tuberosities demonstrate a small proximal lesion adjacent to a sacral body (white arrows) and a larger midline lesion (black arrows) slightly distal to the expected location of the coccyx that extends into the left ischioanal fossa fat pad. (c) Sagittal fat-saturated rapid acquisition T1-weighted MR image demonstrates the same lesions. (d) T2-weighted, (e) T1-weighted fat-saturated, and (f) contrast-enhanced T1-weighted fat-saturated MR images demonstrate slightly atypical features with moderate T1 and T2 lesion intensity and typical heterogeneous and septal enhancement.

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May 1, 2018 | Posted by in NEUROSURGERY | Comments Off on Radiologic Findings and Differential Diagnosis of Chordomas in the Spine
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