Management of spinal metastasis is a large and challenging clinical problem. For metastatic epidural spinal cord compression, a prospective, randomized, controlled trial showed the utility of circumferential surgical decompression followed by adjuvant radiotherapy. In the setting of those data, surgical techniques evolved from decompressive laminectomy only to anterior corpectomy to posterior-only transpedicular corpectomy. The transpedicular approach has recently been modernized with minimally invasive and mini-open techniques. This article presents the relevant clinical background on spinal metastasis, reviews the surgical technique for minimally invasive transpedicular corpectomy, and finally reviews relevant results in the literature.
Key points
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For patients with metastatic epidural spinal cord compression, circumferential surgical decompression combined with adjuvant radiotherapy leads to improved ambulation and may improve urinary continence, pain, Frankel scores, and overall survival.
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To achieve circumferential decompression and maintain or restore spinal stability, tumor resection and reconstruction of the anterior spinal column is often required.
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Compared with combined anteroposterior approaches, transpedicular corpectomy has a lower complication rate, lower estimated blood loss, and shorter operative time, and showed improved American Spinal Injury Association scores.
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Typically, minimally invasive cases involve use of tubular retractors at the corpectomy level, but this may inhibit complete vertebral body resection and makes expandable cage placement more difficult, and therefore many surgeons opt for a mini-open approach.
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Compared with open transpedicular corpectomy, minimally invasive spine surgery and mini-open approaches also lead to effective neurologic improvement and pain alleviation, with a trend toward reduced operative times, blood loss, and complication rates.
Introduction: nature of the problem
Spinal metastasis is a large and growing clinical problem. As cancer survivors live longer because of improved adjuvant therapies, the burden of spinal metastasis is expected to increase. Estimates of metastatic epidural spinal cord compression cases range from 8400 to 25,000 annually in the United States, with approximately 76,000 hospitalizations from 1998 to 2006. Among patients dying of cancer, 3.4% are hospitalized annually because of spinal metastasis, with mean hospitalization charges of $61,655 in 2006. A much higher number, between 30% and 90% of deceased patients with cancer, have been found to harbor spinal metastasis in cadaver studies. Older studies showed that breast, lung, and prostate cancers were the most common sources, in descending order. However, a more modern study using the Nationwide Inpatient Sample (NIS) showed a rearranging in relative prevalence: lung cancer (24.9%), prostate cancer (16.2%), multiple myeloma (11.1%), lymphoma (8.7%), breast cancer (6.9%), renal cell carcinoma (3.5%), and colorectal carcinoma (2.1%). Pain and neurologic dysfunction are the most common presenting findings, and appropriate clinical treatment is critically important.
Palliative surgical decompression for spinal metastatic lesions was once a controversial topic. Early data on surgical intervention showed mixed results, likely because of inadequate decompression with laminectomy alone. As surgical treatment advanced to include circumferential decompression, results improved. In 2005, the landmark Patchell study showed definitively that surgical decompression with adjuvant radiation leads to functional neurologic improvement for patients with metastatic epidural spinal cord compression and neurologic deficits. Although the primary outcome was ambulation (84% of the cohort with surgery plus radiation vs 57% of the cohort with radiation alone), improvement was also seen in the secondary outcome measures of urinary continence, pain, Frankel scores, and overall survival. A recent retrospective study even showed a trend toward increased survival with repeat surgery for recurrent spinal metastasis (19.6 vs 12.8 months; P = .085).
The thoracic spine receives 70% of spinal metastases, followed by 20% for the lumbar spine and 10% for the cervical; the vertebral body is the most common site. For patients with spinal instability from a pathologic vertebral body fracture but without neurologic deficit, vertebral augmentation may be a viable treatment option. For others with neurologic deficit from epidural spinal cord compression, corpectomy is often necessary. Early techniques of corpectomy and anterior column reconstruction involved anterior approaches through the thoracic cavity. Since then, extracavitary approaches have grown in popularity because of their more streamlined approach and decreased morbidity. Extracavitary transpedicular corpectomy with expandable cage placement allows for circumferential decompression and anterior column reconstruction from a posterior approach.
Posterior transpedicular corpectomies can be completed from an open, mini-open, or minimally invasive approach. Percutaneous pedicle screw placement has been associated with decreased multifidus atrophy, decreased blood loss, and comparable clinical outcomes relative to open screw placement. Small series on minimally invasive or mini-open approaches for decompression of metastatic epidural lesions have shown promising early results. A systematic review of minimally invasive spine surgery approaches in the management of metastatic spine disease found effective neurologic improvement and pain alleviation, and trends toward reduced operative times, blood loss, and complication rates relative to traditional open approaches. As one such example, this article reviews mini-open extracavitary transpedicular corpectomy for management of these complex metastatic lesions.
Introduction: nature of the problem
Spinal metastasis is a large and growing clinical problem. As cancer survivors live longer because of improved adjuvant therapies, the burden of spinal metastasis is expected to increase. Estimates of metastatic epidural spinal cord compression cases range from 8400 to 25,000 annually in the United States, with approximately 76,000 hospitalizations from 1998 to 2006. Among patients dying of cancer, 3.4% are hospitalized annually because of spinal metastasis, with mean hospitalization charges of $61,655 in 2006. A much higher number, between 30% and 90% of deceased patients with cancer, have been found to harbor spinal metastasis in cadaver studies. Older studies showed that breast, lung, and prostate cancers were the most common sources, in descending order. However, a more modern study using the Nationwide Inpatient Sample (NIS) showed a rearranging in relative prevalence: lung cancer (24.9%), prostate cancer (16.2%), multiple myeloma (11.1%), lymphoma (8.7%), breast cancer (6.9%), renal cell carcinoma (3.5%), and colorectal carcinoma (2.1%). Pain and neurologic dysfunction are the most common presenting findings, and appropriate clinical treatment is critically important.
Palliative surgical decompression for spinal metastatic lesions was once a controversial topic. Early data on surgical intervention showed mixed results, likely because of inadequate decompression with laminectomy alone. As surgical treatment advanced to include circumferential decompression, results improved. In 2005, the landmark Patchell study showed definitively that surgical decompression with adjuvant radiation leads to functional neurologic improvement for patients with metastatic epidural spinal cord compression and neurologic deficits. Although the primary outcome was ambulation (84% of the cohort with surgery plus radiation vs 57% of the cohort with radiation alone), improvement was also seen in the secondary outcome measures of urinary continence, pain, Frankel scores, and overall survival. A recent retrospective study even showed a trend toward increased survival with repeat surgery for recurrent spinal metastasis (19.6 vs 12.8 months; P = .085).
The thoracic spine receives 70% of spinal metastases, followed by 20% for the lumbar spine and 10% for the cervical; the vertebral body is the most common site. For patients with spinal instability from a pathologic vertebral body fracture but without neurologic deficit, vertebral augmentation may be a viable treatment option. For others with neurologic deficit from epidural spinal cord compression, corpectomy is often necessary. Early techniques of corpectomy and anterior column reconstruction involved anterior approaches through the thoracic cavity. Since then, extracavitary approaches have grown in popularity because of their more streamlined approach and decreased morbidity. Extracavitary transpedicular corpectomy with expandable cage placement allows for circumferential decompression and anterior column reconstruction from a posterior approach.
Posterior transpedicular corpectomies can be completed from an open, mini-open, or minimally invasive approach. Percutaneous pedicle screw placement has been associated with decreased multifidus atrophy, decreased blood loss, and comparable clinical outcomes relative to open screw placement. Small series on minimally invasive or mini-open approaches for decompression of metastatic epidural lesions have shown promising early results. A systematic review of minimally invasive spine surgery approaches in the management of metastatic spine disease found effective neurologic improvement and pain alleviation, and trends toward reduced operative times, blood loss, and complication rates relative to traditional open approaches. As one such example, this article reviews mini-open extracavitary transpedicular corpectomy for management of these complex metastatic lesions.
Preoperative planning
Considerable preoperative planning is required before undertaking a minimally invasive transpedicular corpectomy for spinal metastasis. Discussion with a medical and radiation oncologist is necessary to determine propriety for surgery. Multiple complementary imaging modalities aid surgical planning. Use of neuromonitoring and discussion with anesthesia regarding perfusion goals enhances patient safety.
Oncologic Consultation
For patients with new diagnoses of spinal metastasis, consultation with both a medical oncologist and a radiation oncologist is suggested. Patchell criteria for spinal decompression include nonmedical primary tumors and expected survival of at least 3 months. The medical oncologist can ensure completion of staging to estimate survival. The medical oncologist can additionally comment on cancer-related or medically related comorbidities that may preclude surgery. For example, many patients with cancer have immunosuppression and/or poor nutritional status that diminish the chances of successful postoperative recovery. If the burden of illness is too high or expected survival is less than 3 months, the patient is likely a poor candidate for surgical intervention.
A radiation oncologist may also be consulted to assess the radiosensitivity of the lesion. Metastatic spine lesions from radiosensitive leukemia, lymphomas, germ-cell tumors, and multiple myeloma are usually better treated with radiation alone. If deemed appropriate for surgery, there is still a role for discussion and planning of adjuvant postoperative radiation. Traditionally, postoperative radiation consisted of conventional external-beam radiotherapy delivered in 10 fractions of 3 Gy each. However, stereotactic radiosurgery is an emerging therapy with improved local control. Many tumors that are traditionally considered radioresistant do actually respond to stereotactic radiosurgery, and in some of these cases surgery may not be necessary. These examples include renal cell carcinoma and colon cancer. The radiation oncologist can be helpful in discussing the optimal extent of intended surgical resection. Nonetheless, cases of acute neurologic deficit and/or instability generally require surgical intervention.
Imaging
Radiograph, computed tomography (CT), and magnetic resonance imaging (MRI) provide complementary information and should all be part of the preoperative planning when possible. If the spine is sufficiently stable and the patient can tolerate upright radiographs (sitting or preferably standing), sagittal balance can be assessed under weight-bearing conditions. These imaging modalities can often reveal significant abnormalities not obvious on a supine examination. CT is best for evaluating bone quality and extent of tumor invasion. The number of levels requiring vertebrectomy and reconstruction can then be determined. Additionally, measurements of adjacent pedicle size are useful in the planning of implanted hardware. MRI is best for visualizing the neural elements and assessing the exact locations of spinal cord or nerve compression. Gadolinium-enhanced MRI sequences precisely define the tumor anatomy and may reveal subtle findings not readily visible on CT. Fig. 1 shows preoperative imaging in a case example involving a 56-year-old man with metastatic melanoma to T10.
Angiography/Embolization
Preoperative angiography is generally not required but should be considered for vascular tumors. Angiography can define the tumor vasculature and influence the surgical approach. In particular, identification of the segmental level and side of the artery of Adamkiewicz helps the surgeon avoid compromise of this important segmental feeder. For vascular tumors such as renal cell and thyroid carcinoma, preoperative embolization of important feeding vessels can decrease intraoperative blood loss. However, risk of intraoperative blood loss must be weighed against risk of neurologic deficit from preoperative embolization, as high as 25% in some series.
Neuromonitoring
Use of real-time neuromonitoring is a helpful adjunct for the surgeon performing a transpedicular corpectomy. Somatosensory-evoked potentials (SSEP), motor-evoked potentials (MEP), and electromyographic signals can provide the surgeon with immediate feedback throughout the case. The mechanism of transpedicular vertebral body resection often destabilizes the spine, and the authors typically use temporary rod placement to protect against unplanned translation of the spinal column. Any spinal translation could stretch or kink the cord and may result in MEP or SSEP changes. Similarly, any downward pressure on the cord during surgery could cause injury. If alerted by MEP or SSEP changes, the surgeon may pause surgery, make technical adjustments, and/or request an increased mean arterial pressure (MAP) to aid in cord perfusion.
Use of Approach Surgeon
An approach surgeon is not needed for the posterior mini-open transpedicular carpectomy, which is a major advantage over open anterior thoracoabdominal or open lateral approaches.
Anesthetic Concerns
Open discussion with anesthesia before incision is helpful to protect neural function. It is important to remember that the most common indication for spinal tumor surgery is epidural spinal cord compression. The compressed spinal cord is already in a compromised position. Further hemodynamic insults with episodes of hypotension may add risk of spinal cord injury. A clear MAP goal can be discussed with the anesthesiologist and maintained for the duration of the case. A common goal is to maintain MAP greater than 85 mm Hg. If any episodes of hypotension occur during the case, a surgical pause can allow the anesthesiologist to correct the MAP before resuming surgery.
Intraoperative Imaging
The surgeon must choose between intraoperative plain films, fluoroscopy, and/or CT scan to localize the level of interest. Sometimes the pathologic level is easy to visualize because of fracture, loss of vertebral body height, and/or pathologic angulation. However, the thoracic spine is notoriously difficult to visualize, especially in obese patients. The authors recommend localization in the thoracic spine with anteroposterior views identifying the C7-T1 junction. It is critical to understand that the T1 rib is broad, round, and extremely close to the T2 rib. However, rib counting on intraoperative radiographs can be challenging. For patients with a large body habitus, an abnormal number of ribs, or transitional lumbar vertebrae, or for those harboring small metastatic lesions, preoperative CT-guided fiducial screw placement decreases localization time and radiation exposure and helps avoid wrong-level surgery.
Surgical approach
Preparation and Patient Positioning
After general anesthesia is induced, the patient is placed prone on the operating room table. A Jackson table is favored because of its radiolucence. This feature is particularly important if an anteroposterior radiograph is used for localization. All pressure points are padded. The authors tuck the arms for thoracic spine abnormalities. A preoperative radiograph is taken to localize the level. The patient’s skin is sterilely prepped and surgical drapes are applied with sufficient space to span the planned upper and lower instrumented vertebrae and to allow for localization.
Surgical Procedure
Although multiple percutaneous stab incisions are a viable option, the authors prefer a single midline skin incision but separate fascial incisions. In their experience (and also the experience of Dr Rick Fessler and Dr Michael Wang), the single midline incision leads to better postoperative cosmesis. Hemostasis is obtained with monopolar electrocautery. The dissection is then performed in the extrafascial plane to minimize disruption of the fascia and the underlying soft tissues.
Intraoperative radiography is used to confirm the intended surgical levels. Using a posterior pedicle screw fixation system, the authors then place minimally invasive pedicle screws at least 2 and often 3 levels above and below the intended corpectomy level. This procedure is generally performed with fluoroscopic guidance. Image-guided screw placement is also an option that may minimize radiation exposure to the surgeon and operating room staff. For fluoroscopic guidance, Jamshidi needles are first introduced into the pedicles. From an anteroposterior view, the lateral aspect or midpoint of the pedicle is targeted. The Jamshidi is first gently docked in the cortical bone with a mallet. A lateral image is then taken to ensure a trajectory parallel to the pedicle. After correcting the trajectory, anteroposterior imaging should be used during the first 15 to 20 mm of Jamshidi advancement, taking care not to breach the medial pedicle border and risk entry into the spinal canal. After reaching this depth with no medial breach, the Jamshidi should be advanced a few millimeters further into the vertebral body under lateral fluoroscopy. A Kirschner wire (K-wire) is then gently placed through the center of the Jamshidi needle into the vertebral body. Once the K-wire is docked a few centimeters into the vertebral body, the Jamshidi is carefully and slowly removed. The K-wire should be held in place with a needle driver or hemostat while removing the Jamshidi to prevent inadvertent K-wire removal, which would necessitate restarting the procedure.
Once the Jamshidi is removed and the K-wire is retained at a suitable depth, a cannulated tap and then a cannulated screw is placed over the K-wire. Frequent lateral imaging is a critical safety mechanism during screw advancement. Friction from the cannulated screw can easily carry the K-wire anteriorly through the front of the vertebral body during screw advancement. This important pitfall must be avoided to prevent injury to the aorta, pleura, and other vital structures ventral to the vertebral body. Through bobbing the K-wire up and down by a few millimeters during the placement of the screw, the surgeon can avoid the problem of the K-wire being forced anteriorly during screw placement. Once the cannulated screw is advanced through the pedicle and into the vertebral body, the K-wire can be safely removed. The screw can then be advanced to the final desired depth. The same procedure is then repeated to place the remaining pedicle screws. Fig. 2 illustrates the technique for minimally invasive pedicle screw placement.
Related posts:
Minimizing Radiation Exposure in Minimally Invasive Spine Surgery
Current Techniques in the Management of Cervical Myelopathy and Radiculopathy
Minimally Invasive Treatment of Thoracic Disc Herniations
Percutaneous Pedicle Screw Fixation for Thoracolumbar Fractures
Miniopen Pedicle Subtraction Osteotomy
Lateral Transpsoas Lumbar Interbody Fusion
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