A sixteen-year-old boy was seen because of a four-month history of stiffness and severe pain in the thoracolumbar region of the back. Physical examination demonstrated tenderness in the area of the posterior elements of the eleventh and twelfth thoracic and first lumbar vertebrae, without neurological deficit.
Plain radiographs showed increased bone density at the level of the twelfth thoracic vertebra and diffuse sclerotic changes in the paravertebral soft tissues at the levels of the eleventh thoracic through second lumbar vertebrae (Figs. 1-A and 1-B). The computerized tomography scan demonstrated that the tumor included the entire twelfth thoracic vertebra as well as segments of the eleventh thoracic vertebra. There was extensive paravertebral and epidural involvement in the region of the eleventh thoracic through first lumbar vertebrae as well as bilateral invasion of the paraspinous muscles in the region of the eleventh thoracic through second lumbar vertebrae (Fig. 2). A T1-weighted axial magnetic resonance image demonstrated low signal intensity in the region of the tumor, whereas a T2-weighted axial image demonstrated an irregular mix of low signal intensity and high signal intensity in that region. The T2-weighted axial image also demonstrated a halo of high signal intensity around the portion of the tumor in the paraspinous muscles. The magnetic resonance images suggested that the tumor consisted of mineralized parts (bone and calcified tissue) as well as non-mineralized parts (osteoid, fibrous, and vascular tissue) and that there was edema around the portion of the tumor in the paraspinous muscles.
A histological diagnosis of osteosarcoma was made on the basis of the findings of open biopsy, which was performed four months before the index operation. With use of a 14-gauge trephine, a biopsy specimen was taken from the body of the twelfth thoracic vertebra through the right pedicle. The biopsy track was seen on the computerized tomography scan of the twelfth thoracic vertebral level (Fig. 2). The tumor was classified as stage IIB according to the system of the Musculoskeletal Tumor Society3 and as type 6 (invasion of adjacent vertebrae) according to our own system11. No evidence of metastasis was observed on a total-body computerized tomography scan, a technetium-99m scan, or a gallium scan. Preoperatively, the patient had five courses of adjuvant chemotherapy consisting of carboplatin (450 milligrams), pirarubicin (100 milligrams), and high-dose methotrexate (fifteen grams).
Spinal angiography and selective embolization of the feeder segmental artery were performed one day before the operation.
Operative Procedure
En Bloc Laminectomy and Posterior Spinal Instrumentation
With the patient in the prone position, a posterior midline longitudinal incision was made. The posterior elements were exposed through healthy paraspinous muscles without exposing the biopsy track, and a wide margin of muscle was left attached to the posterior elements.
The most lateral extent of each transverse process of the eleventh thoracic through second lumbar vertebrae was exposed bilaterally, as were the eleventh and twelfth ribs. The ribs were transected two to five centimeters lateral to the costotransverse joint. The parietal pleura then was separated bluntly from the lateral side of each vertebra.
Next, pediculotomy and en bloc laminectomy were done with use of a specially manufactured stainless-steel wire saw with a 0.54-millimeter diameter (threadwire saw; Tomita and Kawahara, Kanazawa, Japan)11. The saw was inserted, through an epidural catheter, into the epidural space beneath the laminae of the eleventh thoracic through second lumbar vertebrae and was pulled through the intervertebral foramen between the tenth and eleventh thoracic vertebrae and that between the second and third lumbar vertebrae. When both ends of the saw were pulled tightly in a lateral direction, the saw ran adjacent to the inner wall of the pedicles of the eleventh and twelfth thoracic and first and second lumbar vertebrae. With a reciprocating motion of the saw, thin cuts were made through the four pedicles. After pediculotomy had been performed on both sides, the laminae of the eleventh and twelfth thoracic and first and second lumbar vertebrae, as well as the paraspinous muscles that had been invaded by the tumor, were removed en bloc.
Cotrel-Dubousset posterior spinal instrumentation was then inserted. First, the plain anteroposterior and lateral radiographs, as well as the computerized tomography scans of the vertebrae into which the pedicle screws were to be inserted, were meticulously checked. The entrance points of the screws were selected to be one millimeter caudad and five millimeters lateral to the middle of the facet joint, and the screws were to be directed medially at a 10-degree oblique angle. To check the position of the screw-holes in the pedicles, metallic pins were inserted into the holes and anteroposterior and lateral radiographs were made. The pedicle screws were placed into three vertebrae cephalad and three vertebrae caudad to the affected vertebrae. Rods that were contoured to restore the physiological alignment of the spine in the sagittal plane were attached to the pedicle screws.
En Bloc Corpectomy and Reconstruction of the Spinal Column
The pleura and the insertion of the diaphragm were separated from the vertebrae and the ribs, with care being taken not to damage the pleura or the diaphragm. The eleventh and twelfth intercostal and first lumbar nerves were cut bilaterally, and the eleventh and twelfth intercostal and first lumbar arteries were ligated and carefully reflected. The eleventh and twelfth thoracic and first lumbar vertebrae were separated from the thoracoabdominal organs, and a vertebral spatula was inserted from both sides, anterior to the vertebral body, to protect the large vessels and the organs.
The dura mater and the nerve roots at the involved levels were separated carefully from the epidural portion of the tumor, the posterior longitudinal ligament, and the posterior wall of the vertebral body. Then, a cord protector was inserted carefully between the dura mater and the vertebral body to protect the spinal cord for the remainder of the procedure.
Next, two threadwire saws were introduced anterior to the vertebral bodies; one was placed at the caudad end plate of the tenth thoracic vertebral body, and the other was inserted at the level of the disc between the first and second lumbar vertebrae. With a reciprocating motion of the saws, cuts were made in an anterior-to-posterior direction; the bodies of the eleventh and twelfth thoracic and first lumbar vertebrae then were rotated carefully around the spinal cord and were removed en bloc with the tissue margin. A total en bloc spondylectomy was thus accomplished (Figs. 3-A and 3-B). The wound was examined macroscopically for residual tumor tissue, and the operative field was washed copiously and lavaged with a solution containing a high concentration (0.5 milligram per milliliter) of cisplatinum4.
The anterior spinal column then was reconstructed by implantation of a vertebral-body allograft that was augmented with an autogenous fibular strut graft. The allograft (a portion of the thoracic spine that included the fourth through eighth thoracic vertebrae) had been sterilized in an autoclave at 135 degrees Celsius for ten minutes. Anchoring holes for the fibular strut graft were made in the cut surfaces of the tenth thoracic and second lumbar vertebral bodies, and the posterior rods were readjusted to allow compression of the bone graft. Two Cotrel-Dubousset screws were inserted into the bone graft, and a rod was used to connect the two screws. The posterior and anterior rods were connected with use of two low-profile transverse-traction devices of the compact Cotrel-Dubousset system (Figs. 4-A and 4-B). Cancellous bone was obtained from the left posterior iliac crest and was placed around the strut graft and the hardware.
The total operative time was ten hours. The total amount of blood loss was estimated to be ten liters. No chest tubes were necessary.
Postoperative Management
Postoperatively, the patient received an additional five courses of chemotherapy consisting of carboplatin (450 milligrams), pirarubicin (100 milligrams), and high-dose methotrexate (fifteen grams). A circumferential, well molded, full-length body jacket was worn for six months after the operation. At the time of follow-up two years postoperatively, the patient was able to walk without restriction, had no pain, and had normal neurological function except for decreased sensation along the dermatomal distribution of the nerve roots that had been cut. Radiographic examination showed a solid fusion (Figs. 4-A and 4-B). Plain radiographs, a total-body computerized tomography scan, a technetium-99m scan, and a gallium scan demonstrated no evidence of distant metastasis.
Histological Findings
Histological examination of the resected specimen demonstrated that the tumor had had an excellent response to the preoperative chemotherapy. The biopsy track had been included in the total resection. Examination of the sagittal sections showed that the discs were not involved and that the portion of the tumor involving the spinous process was surrounded by supraspinous and interspinous ligaments (Fig. 3-B). Examination of the axial sections demonstrated that both the paravertebral and the epidural portions of the tumor were covered completely with a pseudocapsule (Figs. 5-A and 5-B). The margin of excision was considered to be marginal or more than marginal, except at the pedicles, where the margin was intralesional. We used Enneking's definition of a marginal margin, which states: "A marginal margin means that the lesion has been removed en bloc, that the plane of dissection has been extracapsular, either between the (pseudo)capsule and the reactive zone or within the reactive zone, and that the margin of the wound is composed of reactive tissue. Remaining in the wound are portions of the reactive zone containing satellites and skips in the surrounding normal tissues of the compartment."
Rosen et al. noted that the effectiveness of chemotherapy for osteosarcoma is generally thought to be temporary and that regrowth is inevitable if the primary lesion is not resected. Sundaresan et al. as well as Shives et al. recommended a combination of intensive chemotherapy and complete resection for the treatment of a primary spinal tumor.
En bloc resection of a vertebral tumor was attempted by Stener and by Roy-Camille et al., but the procedure described by those authors consisted of an en bloc corpectomy and piecemeal resection of the posterior arch. In a patient in whom the laminae and the para spinous muscles are involved, this procedure probably causes a large amount of contamination by tumor cells.
We modified the techniques of Stener and Roy-Camille et al. to achieve an en bloc resection of the entire vertebra (both the anterior and the posterior component). As described earlier, we used a threadwire saw11 to cut through the involved pedicles. The primary advantage of this saw compared with the Gigli saw is that it has a smooth surface, which causes less injury to the soft tissue; in addition, it is more flexible and easier to manipulate. The diameter of the saw (0.54 millimeter) allows for a sharp, thin cut to be made with minimum contamination of the margin with tumor cells.
As the margin of excision at the pedicles was intralesional rather than marginal, local recurrence of the tumor in those areas was of concern to us. Adjuvant chemotherapy has been shown to decrease the prevalence of local recurrence and to increase the rate of cure associated with osteosarcoma when complete killing of all tumor cells is demonstrated in the resected specimen12. We hope that the margins that were obtained with en bloc resection and the successful histological response of the tumor to preoperative chemotherapy are sufficient to prevent recurrence in our patient. Although contamination of the margin of the tumor at the pedicles was unavoidable, we believe that the use of the threadwire saw11 minimized this contamination. In addition, any remaining tumor cells theoretically may be killed by lavage of the wound with a solution containing a high concentration of cisplatinum4.
Another problem that we faced was the spinal reconstruction after total resection of the eleventh and twelfth thoracic and first lumbar vertebrae as well as laminectomy of the second lumbar vertebra. We used a posteriorly placed rod-and-pedicle-screw system that spanned three vertebrae cephalad and three vertebrae caudad to the lesion, as well as an anteriorly placed allograft-autogenous graft construct. Furthermore, we connected anterior and posterior rods with use of the low-profile transverse-traction devices of the compact Cotrel-Dubousset system. Radiographs that were made two years after the procedure showed no dislodgement of the instrumentation or the fibular strut graft and demonstrated a solid fusion between the graft and the vertebral bodies at both the tenth thoracic and second lumbar vertebral levels.
We believe that this procedure, combined with adjuvant chemotherapy, gave our patient the best chance of survival.