The surgical management of vertebral metastases has evolved in recent decades with the refinement of surgical techniques and advancements in spinal instrumentation. Despite these advances, debate exists regarding the best surgical approach for the treatment of thoracolumbar metastases. Improvements in adjuvant treatment strategies have enhanced local and regional tumor control, increasing the survival of patients and redefining the role of surgery. As a result, patients with metastatic disease are living longer, and disease control plays a significant role in their overall prognosis and quality of life. Early diagnosis and management of these lesions become more important not only in improving survival but in controlling pain.
For surgeons treating these lesions, operative management is critical, since surgery may help improve quality of life, preserve existing neurologic function, and reduce pain. With the development of advanced surgical techniques and a greater understanding of tumor biology, the approaches and instruments available to surgeons now offer better alternatives to laminectomy.
Early studies comparing outcomes for laminectomy and radiation therapy found virtually equivalent results for the two modalities. Because morbidity rates were higher in patients treated operatively, surgery fell out of favor, and radiotherapy became the primary treatment modality for vertebral metastasis. Now that the biomechanics of metastatic vertebral disease are better understood, surgery has increasingly been shown to benefit selected patients. In a randomized, multicenter, nonblinded trial comparing external beam radiation with decompressive surgery and instrumentation followed by external beam radiation in symptomatic patients with spinal cord compression, Patchell and colleagues concluded that aggressive resection of spinal metastases in highly selected patients accompanied by postoperative radiotherapy is superior to radiotherapy alone. Patients treated with surgery retained ambulatory and sphincter function significantly longer than patients in the radiation-only group. In addition, 56% of nonambulatory patients in the surgical group regained the ability to walk, compared with 19% in the radiation-only group. As surgical techniques have evolved, several approaches, including the ventral transthoracic and various dorsal forms, have shown surgical outcomes superior to those of radiation treatment in historical controls when used alone or in combination.
The optimal surgical treatment for solitary and multiple metastases is controversial and continues to be argued. Both en bloc and palliative strategies have been discussed. Indications for these interventions continue to change with the advent of stereotactic radiosurgery and cement augmentation. When surgery is indicated, surgical technique is largely defined by several factors, including tumor histologic features, tumor location, number of levels involved, the patient’s neurologic condition, and the presence of deformity. Medical comorbidities, extent of systemic disease, and anticipated life expectancy also factor into the decision-making process. Since their introduction, the Tokuhashi and Tomita algorithms have been used by surgeons to help determine the potential benefit of surgery for selected patients. Surgical intervention has traditionally been recommended in cases of progressive neurologic deficit, mechanical instability, an enlarging radioresistant tumor, and intractable pain unrelieved by nonsurgical treatment.
Debate continues over the approach that best minimizes overall morbidity in patients who have limited survival. Given the heterogeneous nature of these tumors, the surgical treatment for patients with metastatic spinal tumors remains highly individualized, with tumor histologic characteristics being the main determinant of survival. Each patient requires a thorough diagnostic and medical assessment, and the decision to operate must consider the risks of surgical morbidity and death along with the potential for gains in both the duration and quality of survival.
Using the best available evidence, this chapter compares the combined ventral and dorsal approach with the lateral extracavitary approach. Through a case illustration, the advantages of the lateral extracavitary approach are highlighted.
A 50-year-old woman had recurrent breast metastases to the thoracic spine following previous laminectomy, decompression, and radiotherapy for epidural metastases. At initial presentation she had high-grade paraparesis that improved with surgery and radiation. No other systemic metastases were identified either initially or upon recurrence.
PMH: Estrogen receptor–positive invasive ductal carcinoma of the breast treated with resection and hormonal therapy; mitral valve prolapse
PSH: Laminectomy and decompression at T8 followed by radiotherapy at 30 Gy in 10 fractions to the thoracic spine
Exam: At the time of recurrence, she had worsening gait instability, numbness, and weakness in her lower extremities.
Imaging: Magnetic resonance imaging (MRI) of the thoracic spine demonstrated bulky, infiltrating metastases from T7 to T9 with paraspinal and epidural extension. Circumferential encasement of the spinal cord was evident, with marked compression and cord edema ( Figure 16-1 ). A preoperative angiogram was obtained that demonstrated arterial supply to the tumor by the right T7 and bilateral T8 radicular arteries. Successful embolization was performed with no tumor blush evident after embolization ( Figure 16-2 ).
Combined Ventral and Dorsal Approaches
In the treatment of thoracolumbar metastasis, several surgical options exist for resection, decompression, and stabilization. Thoracic corpectomies have traditionally been performed from a ventral approach via sternotomy or thoracotomy. These approaches allow for direct decompression of the spinal cord, correction of kyphosis, reconstruction of the spinal column, and stabilization.
In general, the ventral approach provides excellent exposure for the resection of epidural extension of vertebral metastases ventral to the spinal canal. These can be visualized directly and decompressed with complete resection of the involved body. For resection of lesions at T1 to T3, a sternotomy or manubrial window can be used if needed. This is performed from the patient’s left side, because the recurrent laryngeal nerve has a deeper course on the right side and there is less chance of injury. However, the thoracic duct is at risk for injury with the left-sided approach. The great vessels may be retracted to allow visualization of T1 to T3, and the brachiocephalic vein may need to be ligated and incised for better visualization. Following corpectomy, structural grafts are positioned and a plate may be applied. Due to variances in anatomy and thoracic kyphosis, this may preclude placement of ventral instrumentation, which then necessitates dorsal fixation.
For lesions below T3, a thoracotomy provides access at multiple levels. The side of operation often depends on the location of the lesion. The right side is preferable when approaching T3 and T4 because the aortic arch limits visualization of the left side. For lesions located at T5 through T10, the left side is often chosen because the aorta is easier to mobilize and repair than the inferior vena cava if injured.
Combined ventral and dorsal approaches allow circumferential tumor decompression and spinal stabilization. However, this method is associated with greater morbidity, because it requires a staged approach and two separate incisions. Despite the advantages of ventral approaches, the morbidity of thoracotomy and the risk of complications such as pneumothorax, hemothorax, and vascular injury often prohibit their use. Chest tubes are required postoperatively, and patients may require prolonged ventilatory support.
Lateral Extracavitary Transpedicular Approach
Dorsal approaches, including the transpedicular corpectomy, costotransversectomy, lateral extracavitary approach, and modifications thereof, have been used to access the ventral thoracic spine from a dorsal approach. The lateral extracavitary approach was first introduced by Capener in 1954 and subsequently modified and popularized by Larson. Initially described for the treatment of tuberculous spondylitis, this approach has been used for various pathologic conditions, including metastatic vertebral disease. It provides lateral exposure to the thoracic and lumbar vertebrae without entering the pleural or abdominal cavity, which allows better visualization of the ventral dural surface than with other dorsal approaches. In addition to permitting ventral spinal cord decompression, this approach allows the placement of dorsal instrumentation without a second incision. It is usually performed from one side, but can be done bilaterally to facilitate complete spondylectomy, including complete removal of the dorsal elements. Often, it can be combined with a less extensive contralateral transpedicular decompression or costotransversectomy.
Advantages of this approach include the ability to complete the surgery in a single stage, avoidance of a thoracotomy, and a potentially faster recovery period. Rigid dorsal instrumentation is readily accomplished through the same incision and eliminates the need for an additional operation. The ability to remain extrapleural in the thoracic spine eliminates the need for chest tubes and division of the diaphragm.
Despite these advantages, corpectomies from a dorsal approach present specific challenges. Sufficient ventral access, adequate decompression, and risk of pleural and vascular injuries are factors that must be taken into consideration. Resnick and Benzel reported on complications associated with this technique in 33 trauma patients. Eighteen patients experienced complications, with the most common being hemothorax or pleural effusion requiring the use of a chest tube. Other complications included pneumonia, wound infections, cerebrospinal fluid leaks, and incisional hernias.
With this approach, preoperative angiography is sometimes useful in identifying the artery of Adamkiewicz for lesions between T7 and L2, because this artery is located at the level of the lesion in approximately 20% of cases and may provide critical blood supply to the spinal cord. It is also valuable in characterizing the vascular supply to tumors in this region. Endovascular embolization of arterial feeders to these lesions is a useful surgical adjunct that lessens the morbidity of excessive blood loss during surgery.
In this patient a bilateral lateral extracavitary approach was performed with complete spondylectomies and tumor resection at T7, T8, and T9. A curved hockey stick incision was used to obtain adequate dorsal and lateral exposure ( Figure 16-3 ). This allowed pedicle screws to be placed at multiple levels above and below the pathologic levels and provided ventral access to the tumor through a single incision. Pedicle screws were placed bilaterally at T4, T5, T6, T10, T11, and T12. The ventral vertebral column was reconstructed with an expandable titanium cage packed with morselized rib graft ( Figure 16-4 ). The patient was discharged after 10 days and experienced no complications. Her symptoms and neurologic findings continued to improve postoperatively, and at 5-year follow-up there was no evidence of recurrence or instrumentation failure.
After induction of general anesthesia, the patient is positioned prone on a Jackson table and a preoperative radiograph is taken to localize the appropriate level. Several types of incisions can be made, and this is left to the discretion of the surgeon. Variations include straight midline, curved hockey stick, and S- and L-shaped incisions. Regardless of the incision used, sufficient exposure for placement of dorsal instrumentation above and below the pathologic level is planned ( Tips from the Masters 16-1 ).
An exposure that is medial to the erector spinae muscle may provide the desired exposure—without the associated obligatory injury to the erector spinae muscle.
After skin incision, the subcutaneous tissue, thoracolumbar fascia, and paraspinal muscles are stripped from the spinous processes, laminae, facet joints, and transverse processes bilaterally by subperiosteal dissection ( Tips from the Masters 16-2 ). This standard exposure allows for dorsal decompression and placement of pedicle screws. The thoracolumbar fascia is then elevated from the underlying erector spinae muscle and is retracted laterally with the skin and subcutaneous tissue. A plane is developed using blunt dissection under the lateral aspect of the erector spinae muscle. These muscles are then retracted medially off of the underlying ribs. A self-retaining retractor is used to hold the erector spinae muscle medially and the skin flap laterally. At this point, the initial subperiosteal dissection from the midline structures is continuous with the lateral dissection beneath the erector spinae muscle. This allows for simultaneous exposure of the midline dorsal elements and the lateral elements removed subsequently for a lateral approach to the lateral and ventral vertebral body.
A bilateral exposure can provide an enhanced ventral exposure while minimizing blood loss, which often originates from the contralateral ventral epidural space when a unilateral exposure is employed.
The lateral dissection of the erector spinae muscle allows exposure of 8 to 10 cm of rib. This is dissected free from the surrounding soft tissues, including the neurovascular bundle, using a Doyne instrument. The rib head is then disarticulated at the costovertebral joint with a periosteal elevator. Meticulous dissection is performed to avoid tearing the underlying pleura. A rib cutter is used to cut the ribs laterally and the bone is saved for potential graft material. Care is taken to prevent injury to the intercostal nerves and the pleura. This dissection, including rib removal, allows access to the lateral aspect of the vertebral body and pedicle. Three to four vertebral levels can be reached by removing two ribs. The periosteum of the involved vertebrae is bluntly dissected away to identify the disk spaces rostral and caudal to the lesion, and the pleura is retracted to allow proper visualization. Developing this exposure allows an unobstructed view of the lateral aspect of the spine. Similar exposure can be done simultaneously on the contralateral side.
The nerve roots are identified, followed medially to their respective foramina, tied, and incised proximal to the dorsal root ganglia to avoid neuroma formation. The pedicle of the pathologic vertebral body is then removed with a rongeur or drill following dissection of the nerve roots to the medial aspect of the pedicle ( Tips from the Masters 16-3 ). Pedicle removal exposes the lateral aspect of the thecal sac. Compression of the thecal sac by the vertebral tumor is then visualized. The tumor and vertebral body are removed piecemeal and drilled as needed. Downwardly angled curettes are used to push epidural contents into the resection cavity. After the corpectomy is completed, an expandable cage packed with autograft can be placed. Thoracic pedicle screws are then inserted into the levels above and below the pathologic levels.