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

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

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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