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Surgical Management of the Chordomas and Chondrosarcomas of the Thoracic Spine
© 2018 Elsevier Inc. All rights reserved. Please note that the copyright for the original figures submitted by the contributors is owned by Contributors.
Introduction
Chordomas and chondrosarcomas of the spine are malignant primary bone tumors that share several key features. Unlike other malignant primary bone tumors such as Ewing sarcoma or osteosarcoma, their behavior is more indolent. Additionally, aggressive surgical resection can facilitate long intervals of disease control and is the mainstay of treatment, whereas radiation and chemotherapy have limited efficacy against these pathologies.
Chordomas of the Thoracic Spine
Chordomas are rare primary malignant bone tumors that can occur anywhere along the axial skeleton including the thoracic spine. Based on a study by the Surveillance, Epidemiology and End Results program of the National Cancer Institute that looked at 400 microscopically confirmed chordoma cases from 1973 to 2001, 32.0% of cases presented at cranial sites; 32.8% in the cervical, thoracic, or lumbar spine; and 29.2% in the sacrum. The thoracic spine is the least common location for chordoma (13.5%), while the lumbar spine is the most common location in the mobile spine.
Spinal chordomas are slow-growing tumors, so clinical presentation often occurs late stages of the disease and small chordomas often require incidental discovery. Back pain is the most common presenting symptom for spinal chordomas, but since thoracic radiculopathy is less recognizable than cervical and lumbar radiculopathies, thoracic spine imaging may be ordered less promptly than imaging elsewhere in the spine. The insidious and nonspecific nature of the pain frequently delays diagnosis. Neurologic deficit at diagnosis is more common in chordomas of the mobile spine than of the sacrum. It was observed that 22% patients developed metastasis, which portends a poor prognosis, but in these patients, death usually still results from locoregional disease. Metastases most often occur to the lung or the contiguous spine.
Chest X-ray, often ordered for workup of chest wall pain, may show lytic changes in the bone and if the chordoma is large enough, a paraspinous or mediastinal mass. On computed tomographic (CT) scan, chordomas demonstrate lytic bone destruction and calcification in 30%–70% of cases. On T1-weighted magnetic resonance imaging (MRI), chordomas are iso- to hypointense compared with muscle, whereas on T2-weighted imaging, they demonstrate a typical hyperintense and often lobular appearance with septae of low signal intensity. Unlike most other primary bone tumors, chordomas demonstrate limited uptake of radioisotope on bone scanning.
Chondrosarcomas of the Thoracic Spine
Chondrosarcoma is the third most common primary bone tumor, after osteosarcoma and Ewing sarcoma and is characterized by its ability to produce cartilage. Chondrosarcomas occur in the appendicular or axial skeleton, including the skull, but are most commonly found in the pelvis, femur, and shoulder girdle. Spinal chondrosarcomas constitute 12% of the disease. These lesions occur most commonly in the thoracic spine, followed by the cervical and lumbar region. They can arise from the body, the posterior elements, or both. The syndrome hereditary multiple exostoses, also known as diaphyseal aclasis, characterized by multiple osteochondromas, poses significant risk for the development of chondrosarcomas.
Localized pain is the most common presenting symptom, whereas neurologic deficits are less common presenting symptoms. In the thoracic spine, radiculopathy is less likely to be recognized than elsewhere in the mobile spine. High-grade spinal cord compression is unusual on presentation. Chondrosarcoma can metastasize, with the being lung the organ most at risk, and is a strong independent prognostic factor for death. Grade 3 and dedifferentiated chondrosarcomas are most prone to metastasis.
On CT imaging, chondrosarcomas display lytic bone destruction and often house calcifications within, although if they are contained wholly within the vertebral body, they often do not show the calcification pattern but have a sclerotic margin. The following criteria favor a diagnosis of chondrosarcoma: deep endosteal scalloping (greater than two-thirds of cortical thickness), cortical disruption, periosteal reaction, soft tissue mass, and intense radionuclide uptake. It displays low signal intensity on T1-weighted and high signal intensity on T2-weighted MRI and demonstrates peripheral and lobulated rim contrast enhancement, although lesions with limited calcification may show more homogeneous enhancement.
Preoperative Planning
Chordomas have a marked tendency toward recurrence following intralesional excision or biopsy contamination ; seeding tumors along the wound or even intradurally have been reported. Wide resection without violation of the tumor margins is preferred, and this surgical strategy is supported by several large chordoma series. For the purposes of diagnosis, CT-guided core biopsy is preferred over open biopsy as seeding along a small tract is easier to manage than seeding of a surgical cavity.
En bloc resection of chondrosarcoma of the appendicular skeleton has greatly improved the prognosis of the disease, so a similar approach with an emphasis on en bloc resections has been taken with resecting lesions of the axial skeleton. As such, CT-guided core biopsy is imperative to establish the diagnosis of chondrosarcoma prior to commitment to a treatment plan, and the biopsy path should be also within the boundaries of potential excision. Surgical goals include oncologic treatment, pain relief, preserving and improving mechanical stability, and maintaining neurologic function.
Although en bloc resection, with a margin if possible, appears to provide the best rates of locoregional relapse-free survival (LRFS) and overall survival in both chordomas and chondrosarcomas, this surgical strategy has greater risk of complication than intralesional resection. Therefore once an accurate histological diagnosis has been established, a systematic approach for oncologic staging must be pursued. The same surgical techniques and principles apply to both pathologies.
The three key components for staging are as follows: (1) establish tumor grade; (2) define the anatomic relationship of the tumor with osseous, neural, vascular, and visceral structures; and (3) assess for presence of metastasis. Once staging is complete, a multidisciplinary treatment team can decide on the optimal approach for oncologic resection.
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