Primary Tumors of the Spine

Radiologic-Pathologic Correlation

Abstract Introduction

Primary Benign Lesions of the Spine Primary Malignant Lesions of the Spine Conclusions

Source Information References

Primary Malignant Lesions of the Spine

Chordoma

Chordoma is an uncommon tumor, accounting for 2%-4% of all primary malignant bone neoplasms and with an estimated prevalence of 0.51 per million (57,58,59). However, excluding lymphoproliferative neoplasms, chordoma is the most common primary malignant tumor of the spine in adults. These tumors arise from remnants of the notochord, which represents the earliest fetal axial skeleton, extending from the Rathke pouch to the coccyx. This cylinder of tissue is replaced by sclerotomes that produce cartilage and subsequently bone. Normally, the notochord is extruded into the intervertebral regions during this developmental process and evolves into the intervertebral disk nucleus pulposus. Nonneoplastic notochordal vestiges are seen in up to 2% of cadavers, most frequently in the midline near the spheno-occipital synchondrosis and in the sacrococcygeal regions (57). The location of chordomas parallels this distribution, with 30%-35% being in the spheno-occipital region (not discussed further); 50%, the sacrococcygeal region (particularly the fourth and fifth sacral segments); and 15%, other spinal segments (57,58,59). The cervical spine, particularly C-2, and the lumbar spine (Figure 11) are the most common sites of spinal chordoma when it develops above the sacrum.

Chordoma occurs most commonly in middle-aged patients (aged 30-60 years), with the peak incidence in the 5th decade (57). Unlike spheno-occipital lesions, which have an equal sex distribution, spinal chordomas have 2-3:1 male-to-female ratio (57,58,59). Clinical presentation is often subtle, with a gradual onset of neurologic symptoms, including pain, numbness, motor weakness, and incontinence or constipation in sacral lesions. Chordomas are slowly growing lesions and, unfortunately, are often very large, bulky masses when initially discovered.

Pathologically, these lobulated neoplasms are often contained within a pseudocapsule. Histologic analysis reveals elongated cords of clear cells containing intracytoplasmic vacuoles (physaliphorous cells) (Figure 11f). There is abundant mucin, both intracellular and extracellular. Sarcomatous elements (fibrous, chondroid, or osteoid) may also be seen within chordoma, and lesions with these components have been referred to as dedifferentiated chordoma.

The most frequent radiographic appearance of chordoma is that of a destructive lesion of a vertebral body centered in the midline, with a large, associated soft-tissue mass. Osseous expansion is frequent, and evidence of intratumoral calcification is seen in 50%-70% of sacrococcygeal lesions on radiographs and in as many as 90% on CT scans (60,61,62,63) (Figure 11b). The calcification is typically amorphous and often predominates at the periphery of the lesion. Lesions of spinal segments above the sacrum are generally less expansile, have calcification in only approximately 30% of cases, and may contain sclerosis (43%-62% of cases) (60,61,62,63) (Figure 12). In some cases, sclerosis predominates, leading to an "ivory" vertebral appearance. There may be intervertebral disk involvement, with narrowing, which is unusual for most spinal tumors and simulates infection. This appearance has been described in 11%-14% of chordomas and may lead to involvement of two adjacent vertebral levels (57,60,61,62,63) (Figure 12). Similarly, sacrococcygeal chordomas may extend across the sacroiliac joint.

CT demonstrates both the osseous and soft-tissue components of chordoma and the affected surrounding structures. Coronal oblique CT of sacrococcygeal lesions is the optimal method for detecting neural foraminal and sacroiliac joint involvement. In more than 50% of cases, CT shows low attenuation within the soft-tissue mass, which reflects the myxoid-type tissue present pathologically (62,63). A higher-attenuation fibrous pseudocapsule is also common peripherally.

MR imaging, because of its multiplanar capabilities and exquisite contrast resolution, is superior to CT in depicting the extent of chordoma (62,64,65,66). Chordoma is generally low to intermediate signal intensity on T1-weighted MR images and has very high signal intensity on T2-weighted images (similar to the nucleus pulposus) (Figure 11c, Figure 11d, Figure 12c, Figure 12d). This characteristic reflects the high water content of these lesions. High signal intensity has occasionally been reported on T1-weighted MR images in intracranial or spheno-occipital chordomas and is presumably related to the high protein content of the myxoid material. However, this MR imaging appearance is rare with spinal chordomas in our experience. Enhancement of chordoma is commonly seen after intravenous administration of contrast material, either at CT or MR imaging, similar to the vascular blush reported with angiography (64,65,66).

The prognosis of chordoma depends on whether the tumor can be completely resected. The location of the lesion and its very large size at presentation often necessitates incomplete excision. Adjunct radiation therapy may also be employed in the treatment of chordoma. Generally, patients with sacrococcygeal lesions have an improved survival (likely related to the ability to achieve a more complete resection) averaging 8-10 years, compared with 4-5 years for patients with chordomas at other sites (61). Death is often related to local recurrence and invasion rather than to metastatic disease. Metastases develop in 5%-43% of patients, with involvement of the liver, lungs, regional lymph nodes, peritoneum, skin, and heart being the most frequent sites (57,58).

Chondrosarcoma

Chondrosarcoma is the second most common nonlymphoproliferative primary malignant tumor of the spine in adults following chordoma, accounting for 7%-12% of these lesions (67,68,69). The spine represents the primary site in 3%-12% of all chondrosarcomas (67,68,69). Patients typically present with pain and a palpable mass, and neurologic symptoms are apparent in 45% of patients (69). Men are affected two to four times more frequently than women, and the mean age of patients is 45 years. Chondrosarcomas are seen at all levels of the spine, although the thoracic spine is the most common site.

Chondrosarcoma of the spine is usually a relatively low-grade lesion (either grade 1 or grade 2), which likely accounts for the long-term survival of many patients. Most lesions represent primary chondrosarcoma; however, secondary chondrosarcoma may also occur when osteochondroma (solitary or multiple with hereditary multiple exostoses) undergoes malignant transformation.

Radiography of spinal chondrosarcoma typically reveals bone destruction, and lesions may arise in either the vertebral body (15%), the posterior elements (40%), or both (45%) (68,69) (Figure 13). Characteristic chondroid matrix mineralization (rings and arcs) is apparent on radiographs in the majority of patients (70%) but is better delineated by CT (69) (Figure 13b). Cortical destruction is invariably present, and extension into the surrounding soft tissues is common and best depicted by CT or MR imaging. Mineralization is usually apparent in the soft-tissue component of the lesion (Figure 13b). Involvement of adjacent vertebral levels by extension through the disk is seen in approximately 35% of lesions, and adjacent ribs may also be affected in thoracic neoplasms (69,70,71) (Figure 13b). Chondrosarcoma arising from osteochondroma is seen as thickening at the peripheral cartilaginous cap, and large masses may also develop at this site (Figure 10c). At CT, the attenuation of the nonmineralized portion of the lesion is often lower than that of muscle, which reflects the relatively high water content of hyaline cartilage (Figure 10c, Figure 13b). Similarly, MR imaging reveals osseous and soft-tissue involvement by demonstrating low to intermediate signal intensity on T1-weighted images and very high signal intensity on T2-weighted images (Figure 13c, Figure 13d). Areas of mineralization remain low signal intensity regardless of the pulse sequences used; thus, chondrosarcoma usually appears heterogeneous on long repetition time MR images.

Treatment of spinal chondrosarcoma is surgical resection, and vertebral corpectomy with strut bone grafting may be necessary. Cure is possible if the lesion is amenable to complete resection, as reported in 26% of patients in a series by Shives and coworkers (69). However, when wide marginal excision cannot be performed, tumor recurrence ultimately causes death in 74% of cases (67,68,69). Because the tumor is frequently a low-grade lesion, survival is often prolonged, with a mean survival of 5.9 years in the series of Shives et al (69). Radiation therapy is also used as adjunct treatment, but its effectiveness is controversial. Chemotherapy may be used with high-grade and dedifferentiated chondrosarcomas. Distant metastases (with the lung being the most frequent site) are not common with low-grade spinal chondrosarcoma.

Ewing Sarcoma and PNET

Ewing sarcoma and PNET are pathologically distinct entities with very similar characteristics clinically and radiologically. In fact, no radiologic differences have been described, to the best of our knowledge, and their imaging appearances are therefore discussed together. These neoplasms are the most common nonlymphoproliferative primary malignant tumors of the spine in children (1,72,73,74). Lesions of the spine account for 3%-10% of all primary sites of Ewing sarcoma and PNET. However, metastatic foci of Ewing sarcoma and PNET involving the spine are much more common than primary lesions. Patients with both lesions usually present between the ages of 10 and 30 years of age, although the age range is more variable with PNET. Clinical symptoms are pain and neurologic changes, including loss of bowel and bladder function.

The most common location of Ewing sarcoma and PNET in the spine is the sacrococcygeal region, followed by the lumbar and thoracic segments, and only rarely the cervical spine (1,72). The lesions are typically centered in the vertebral body, although extension into the posterior elements is not uncommon.

Histologically, both Ewing sarcoma and PNET are composed of small, round, blue cells, with large irregular sheets of cells divided by septa, scant cytoplasm, and abundant collagen. Areas of osteonecrosis are frequently found in spinal lesions (74). Immunohistochemical studies are needed to distinguish Ewing sarcoma from PNET, with the latter being characterized by neural differentiation. Both lesions share similar cytogenetic features, with translocation of chromosomes 11 and 22 (75).

Radiographs of Ewing sarcoma and PNET may reveal permeative bone lysis, osseous expansion, or sclerosis (72,73,74,75,76,77,78,79) (Figure 14). In the study by Shirley et al (74), diffuse sclerosis was seen in 69% of spinal lesions and was associated with osteonecrosis. CT and particularly MR imaging demonstrate osseous and surrounding soft-tissue involvement to best advantage. Paraspinal soft-tissue masses are often a prominent feature of these lesions. The MR imaging appearance is nonspecific, with lesions having intermediate signal intensity on T1-weighted images and intermediate to high signal intensity on T2-weighted images (72,73,74,75,76,77,78) (Figure 14d, Figure 14e).

Before the advent of chemotherapy, survival of patients with spinal Ewing sarcoma or PNET was dismal because these axial lesions could not be completely resected. However, radiation therapy and chemotherapy are the current mainstays of treatment for spinal lesions, with results approaching 100% for local control and 86% for long-term survival for patients with nonsacral tumors (73). Patients with evidence of instability or neurologic compromise may still require surgical decompression and stabilization. Sacrococcygeal tumors have a worse prognosis, with 62.5% local control and 25% long-term survival, which is most likely related to the larger tumor size because of delayed clinical presentation compared with other spinal lesions (73). Smaller sacrococcygeal foci may be amenable to complete surgical resection.

Osteosarcoma

Osteosarcoma of the spine is rare, accounting for 0.6%-3.2% of all osteosarcomas and 5% of all primary malignant tumors of the spine (80). Patients with spinal osteosarcoma present at an older age (average, in the 4th decade of life) than those with appendicular lesions. There is a male predominance. Patients often present with pain and a palpable mass, and 70%-80% have neurologic symptoms ranging from sensory deficits to paresis (80). Serum alkaline phosphatase levels may be elevated.

Osteosarcomas have been reported at all levels of the spine, although they have a notable predilection for the lumbosacral segments (Figure 15). In most cases, the vertebral body is primarily involved, albeit eccentrically, but secondary extension into the posterior elements is also common. Primary involvement of the posterior elements has been reported in 10%-17% of cases (81).

Pathologically, most spinal osteosarcomas are osteoblastic, although chondroblastic and fibroblastic histologic types have been reported. Occasionally, osteosarcoma (particularly when it is localized to the posterior elements) can be difficult to distinguish from osteoblastoma, both pathologically and radiologically (80,81,82).

Osteosarcoma of the spine may also be a secondary lesion induced by exposure to radiation, with a 5-20 year latent period (80). In addition, spinal osteosarcoma can be a secondary malignancy associated with Paget disease (Figure 16). Although the latter condition very commonly involves the spine, the development of spinal osteosarcoma is disproportionately low (80).

Radiographs of spinal osteosarcoma usually reveal densely mineralized matrix, and an ivory vertebral body may be recognized (79,80,81,82,83,84) (Figure 15a). Loss of vertebral height and sparing of the adjacent disk are common. Purely lytic lesions have also been encountered, although infrequently, and are difficult to distinguish from other solitary lesions of the spine. CT and MR imaging are useful for evaluating lesion extent and the soft-tissue involvement that is frequently seen (Figure 15b, Figure 16b). Lesions with large amounts of matrix mineralization may remain low signal intensity on all MR images, regardless of pulse sequence.

The prognosis of spinal osteosarcoma is dismal. Death usually occurs within 1 year, with only a few patients surviving longer than 2 years (80). The prognosis is poor primarily because the lesions are large at presentation and cannot be completely excised in this location. Adjuvant chemotherapy and radiation therapy are also often employed in treatment.

Abstract Introduction

Primary Benign Lesions of the Spine Primary Malignant Lesions of the Spine Conclusions

Source Information References