10 Minimally Invasive Decompressions for Metastatic Spinal Disease

Keywords: epidural, metastases, minimally invasive, neurologic deficit, radiation, separation surgery, thoracic

True vision is the art of seeing what is invisible to others.

Jonathan Swift

10.1 Introduction

It is inconceivable to have a comprehensive chapter on the management of metastatic spinal disease buried within a minimally invasive primer. In the realm of oncological spine surgery, metastatic disease to the spine is a complex topic with varying and passionate opinions with regard to its management. Fortunately, the work from the Spine Oncology Study Group (SOSG) has provided the necessary framework to assess the stability of the spine in the context of metastatic disease.² The development of the Spinal Instability in Neoplastic Disease Scale (SINS), the work product of the SOSG, reliably determines when a simple decompression is appropriate or when stabilization is required in addition to decompression.^2,3,4,5 The work of the SOSG is mandatory reading for any spine surgeon managing metastatic diseases of the spine, whether that management is minimally invasive or otherwise.

The body of the literature that has arisen regarding “separation surgery” followed by adjuvant stereotactic radiosurgery to achieve local disease control for metastatic disease to the spine continues to build a compelling argument for less invasive surgical strategies.^6,7,8,9 Separation surgery fits hand in glove with minimally invasive approaches for metastatic disease to the spine. The philosophy is to expose the patient to less risk of surgery by making the objective of surgery a separation of the lesion from the spinal cord instead of complete resection of the lesion. What remains is a radiosurgery target.

With the SINS classification system as our framework and separation surgery as our surgical stratagem, the concession I need from the reader for this chapter is this: we have presumed that in each instance discussed in the upcoming pages a simple decompression is the path forward for the patient’s care. Without that concession, the reader and I will become mired in the complexities of biomechanics, tumor volumes, surgical approaches and the like. Decompression of the spinal cord with minimally invasive techniques is the focus of this chapter, not biomechanics. Again, it is the seminal work of SOSG that formed the basis for the decision to proceed with simple decompressions in each case presented in this chapter. By no means does this circumstance dismiss the importance of instrumented decompressions and fusion, which has a well-established role in the treatment of metastatic spinal disease, and they are procedures I routinely perform more often than not for management of this disease entity. However, at times, patients present with unilateral epidural compression in a stable spine with neurologic or impending neurologic deficits. That patient category is the focus of this chapter. For that reason, uninstrumented decompressions are the focus of the case illustrations. Equally important is the presentation of patients who are not candidates for uninstrumented minimally invasive separation surgery.

The very nature of this topic almost mandates that the chapter be constructed around case illustrations that, in turn, become the framework of explaining the technique. Unlike previous chapters in this text, where case illustrations were reviewed at the end of each chapter, this chapter places them front and center. I readily concede that each of these clinical scenarios may have several perfectly viable management strategies that include instrumented fusions, corpectomy, and anterior and posterior reconstructions. Several readers may not necessarily agree with the management strategy employed. Again, I emphasize that it is not the objective of this chapter to have a comprehensive review of these various options. Instead, the aim of this chapter is to review the technique of a minimally invasive decompression of thoracic metastatic lesions. Therefore, the technique selected for the management of each patient for this chapter is an uninstrumented decompression, which may include simple laminectomy, transpedicular decompression or both, depending on the location of the lesion. One statement that should stir little, if any, controversy is that spinal cord compression from a metastatic lesion in a patient with a progressive neurologic deficit is a surgical disease regardless of responsiveness to chemotherapeutic agents or radiation.⁹

The application of minimally invasive techniques for management of metastatic disease of the thoracic spine should come at a time when you have achieved mastery with minimally invasive decompressions of the lumbar spine. I have emphasized the thoracic spine in this chapter for two reasons. The first is that the vast majority of our experience with minimally invasive techniques originates in the lumbar spine. The degenerative processes of the aging spine that benefit from surgical intervention do not present with adequate frequency in the thoracic spine to achieve the same degree of comfort in that region of the spine. However, translating that lumbar skillset to decompression of metastatic lesions in the thoracic spine, while adding a level of complexity, can be relatively straightforward. As with any minimally invasive technique, a more refined understanding of the three-dimensional anatomy of the thoracic spine is essential.

Second, while metastatic lesions may occur throughout the entire spine, a review of my experience suggests that symptomatic spinal cord compression requiring surgical intervention occurs with greater frequency in the thoracic spine than in either the cervical or lumbar regions. The greater surface area of this region undoubtedly results in a higher statistical probability that a lesion will surface within one of the 12 thoracic vertebrae, more so than the lumbar or cervical regions. The literature has corroborated what I have found in my clinical practice. The various reviews in the literature report the thoracic spine as the most common site of metastasis, up to 70% of the time, followed by the lumbar spine representing 20% and the cervical spine with 10%.10,11

As you proceed with minimally invasive approaches in the thoracic spine, keep in mind the distinct topography of the thoracic spine when compared to the lumbar spine. While the anatomical regions are distinct, there are more similarities than differences. Understanding those unique elements of the thoracic landscape is a key component for the application of these techniques and successful decompression of the spinal cord due to metastatic disease.

In this chapter, the clinical cases are central to the surgical technique, and as such, they are discussed in great detail. Unlike the relative uniformity of the laminectomy or microdiscectomy, every metastatic lesion is truly unique. As a result, it is impossible to present one standard approach for the management of this clinical entity. Instead, I have selected several case illustrations, with the hope that the variations between them cover minimally invasive surgical management in greater depth than presenting a standard surgical technique section could.

Finally, before embarking on this topic, I cannot emphasize enough the importance of a multidisciplinary approach. In the absence of a neurologic emergency, it is imperative to have a clear line of communication with both the radiation and medical oncologists before determining a plan of care. An inextricable component of any treatment plan is knowledge of the underlying primary neoplasm. Understanding the biology of that primary neoplasm in the context of a patient who may have a single metastatic lesion or multiple lesions helps define and guide the role of surgical management. Furthermore, the knowledge that a neoplasm is exquisitely responsive to radiation or chemotherapy may further influence the role or the extent of surgery. Incorporating the aforementioned allows you to harness the advantages of minimally invasive techniques so they work in conjunction with radiation and chemotherapy in order to optimize the outcome for the patient. The presence of a metastatic lesion or lesions in the spine does not always equate to surgery. The vast majority of patients I see will not need an operation at all. The absence of a neurologic deficit provides you with the gift of time; take full advantage of it. Communicate with your colleagues in radiation and medical oncology and listen to their thoughts on the matter. Over the years, I have found it of tremendous value to know what my colleagues have in mind for the patient and how surgery fits into that plan of care.

10.2 Rationale

As already mentioned several times throughout this text, a smaller paramedian incision with a table-mounted access port that offers a focused exposure in lieu of a longer incision with self-retaining retractors allows for optimal blood flow to the muscles and skin edge during the procedure and limits the amount of tissue necrosis that may occur after the procedure. Therefore, a minimally invasive paramedian approach creates an ideal environment for healing in a patient population that may already be challenged with nourishment and facing further challenges to healing a wound through radiation and chemotherapy. The ability to begin adjuvant therapies almost immediately after a minimally invasive decompression without significant concern for wound healing may be far and above the greatest advantage of this approach.

In writing this chapter, I reviewed the patterns of spinal cord compression in the management of metastatic disease to the spine in my practice over the last 10 years. Patients who present with spinal cord compression from a lesion in the epidural space off to one side are ideal candidates for a paramedian minimally invasive resection. At times, the metastatic disease appears to originate from the vertebral body and then extend into the pedicle. From the pedicle, the disease expands into the epidural space, causing compression of the spinal cord off to one side. At other times, the lesion seems to originate in the epidural space but still cause compression predominantly on one side. Such laterality lends itself exceptionally well to a minimally invasive approach, where the lateral recess, epidural space and pedicle may all be readily accessed. A minimally invasive approach spares the posterior tension band and the spinous process, which is a biomechanical asset, provided no metastatic disease is present within the posterior tension band and the spinous processes. If the spinous processes are involved, this asset all of sudden becomes a liability. Careful consideration should be given to a traditional midline open approach if the procedure is not simply a palliative one.

Patients who present with circumferential compression of the spinal cord need a different strategy.▶ Fig. 10.1 describes a 52-year-old woman 4 years after an initial diagnosis of colon cancer, who presented with circumferential compression of the spinal cord at T9. Her oncologist referred her for minimally invasive separation surgery, but the pattern of compression did not lend itself to such an approach. She underwent a midline costotransversectomy approach to the T9 body for corpectomy, placement of cage and posterolateral instrumentation from T6–T11 (▶ Fig. 10.2).

For all minimally invasive decompressive separation surgeries, I use an expandable minimal access port, which allows simultaneous exposure of the medial and lateral structures during the decompression. I have found that a greater area of exposure is also helpful when obtaining hemostasis which, in the metastatic tumor resections, is no small task. Rare is the occasion where I can find an 18-mm diameter adequate for the work I need to accomplish in the decompression of a metastatic lesion, so much so that I have not included a fixed diameter minimal access port among the cases in this chapter. The cases I performed with fixed diameter access ports were part of my learning curve that convinced me to use an expandable access port. I feel that the advantages offered by an expandable access port far outweigh the liability of a few more millimeters to the incision.

Regardless of the method used for localization, all patients are positioned on a Jackson table. No Wilson frame is used for the simple reason that the gears from the frame can be seen on AP fluoroscopic images. Those same gears create scatter on the intraoperative CT images. Thus, the Wilson frame may obscure visualization of the bony anatomy during either fluoroscopy or computer-assisted navigation.

The patient was found to have a 2.9-cm lung lesion with pleural effusion on CT of the chest for evaluation of his cough. Metastatic disease was also identified in his liver. Further analysis of the CT demonstrated widely metastatic disease to the cervical, thoracic and lumbar spine, encompassing the entire vertebral body of C3 (resulting in a pathological fracture), the left transverse process of T7, the pedicle and transverse process of T9 on the left, the spinous processes of L1 and L2 and the lateral aspect of the vertebral body at L4 and L5. A subsequent magnetic resonance imaging (MRI) of the cervical, thoracic and lumbar spine demonstrated that the pathological fracture at C3 (not shown) and the lesion of T9 (▶ Fig. 10.3) were the only lesions causing spinal cord compression. There was no evidence of metastatic disease to the brain. Subsequent biopsy demonstrated this lesion to be non-small-cell adenocarcinoma of the lung.

The T9 lesion was the most likely cause of his presenting symptoms, since he was asymptomatic in his upper extremities but symptomatic in his lower extremities. However, concern for the stability of the cervical spine in the context of a pathological fracture at C3 and the need to position the patient prone for a thoracic decompression prompted a C3 corpectomy with C2–4 arthrodesis.

The location and configuration of the lesion at the T9 level favored a minimally invasive approach. The compression originated from the left lamina and extended into the pedicle. There was involvement of the transverse process and rib head. Given the unique configuration of the metastatic lesion around the spinal cord, I recommended a minimally invasive hemilaminectomy, transpedicular decompression with partial costotransversectomy.▶ Fig. 10.4 demonstrates the conceptual surgical strategy with the access port.

Intervention

The patient was positioned prone on a Jackson table. Since this lesion was at T9, the arms were brought forward on arm boards. I used fluoroscopy for localization of the level. A preoperative lumbar radiograph confirmed 5 non–rib-bearing vertebral bodies. A preoperative AP radiograph of the thoracic spine demonstrated the lesion within the pedicle (▶ Fig. 10.5). Recognizing this phenomenon is one of those tremendously helpful findings on a radiograph that can help in the localization process at the time of surgery, the key element of which is actually making the observation. As mentioned throughout this chapter, localization in the thoracic spine is an unforgiving endeavor. For a minimally invasive approach, it is even more so.

Localization

Any localization for a level in the thoracic spine should be a systematic process utilizing both AP and lateral imaging that allows confirmation of the level counting from the sacrum upward (after 5 non–rib-bearing vertebrae have been confirmed). I localize the level in two phases. The first is a preliminary preoperative localization, where I confirm the level with a series of spinal needles and then mark the entry points for those spinal needles, so that I may repeat the process efficiently after draping the patient.

Before the patient is prepped and draped for the actual surgery, I prep him widely for the purpose of localization, but I do not drape the patient. The prepped area includes the lumbar and thoracic spine. I put on a pair of sterile gloves and have at my immediate disposal 5 spinal needles, both 18 and 20 gauge. I begin by palpating the anterior superior iliac spine and the interspinous process space. This location places me at L4–5 or L3–4. I pass a spinal needle 2 cm off the midline onto the lateral aspect of the lamina–facet complex. Since the lesion is on the left, the localizing spinal needles are all placed on the right except for the spinal needle intended to identify T9. From there, I palpate the interspinous process space, and after every three levels, I pass another spinal needle. My first objective is to confirm T12. After the placement of three spinal needles, I obtain a lateral fluoroscopic image to confirm the current position of the needles. In this case, the first lateral image demonstrated that my first needle was at S1, and the second needle was pointing to the pedicle of L3 (▶ Fig. 10.6a). I then have the fluoroscopic technician roll the fluoroscope toward the head, while keeping the L3 spinal needle in the field of view, which allows me to confirm the spinal needle in position at T12. I adjust the needle at T12 so that it is precisely parallel to the pedicle of T12 (▶ Fig. 10.6b). Having the needle in this position makes it easier to confirm AP images. I obtain an AP image (not shown) to confirm that I am at the first rib-bearing vertebra. In this manner, I confirmed my spinal needle at T12 on AP and lateral imaging.

I repeat the process of sliding the fluoroscope toward the head, moving the T12 spinal needle to the bottom of the field of view and allowing me to visualize T9. I now pass a spinal needle onto T9, keeping in mind that this segment is riddled with metastatic disease. The needle has the potential to pass right through the diseased bone. As I pass the needle, I may take intermittent images with the fluoroscope until I feel that I have reached the spine or can see that I am at the level of the spine. Once I have confirmed my level at T9 on an AP image, I have completed my preoperative localization. I plan an incision 3 cm off the midline over the T9 level, which is 3.0 cm in length, and mark all the entry points of the needles for a second confirmation when the area is prepped and draped.

After prepping and draping the entire lumbar and thoracic spine, I begin by placing the spinal needles into their previous locations and reconfirming the levels with both AP and lateral fluoroscopic images. This step is part of a check and balance system to ensure the highest degree of certainty that after making the incision and exposing the anatomy, the lesion resides well within my grasp. The spinal needles are all kept in position to guide docking of the minimal access port.▶ Fig. 10.6c demonstrates a lateral fluoroscopic image where the spinal needle is in position while the dilation of the muscle is taking place.▶ Fig. 10.6d illustrates an AP fluoroscopic image where the expandable minimal access port is in position on the side of the lesion (left), and the spinal needle remains in position on the opposite side of the lesion pointing to T12. Even after the access port is in position, I leave the spinal needles in position until I have directly visualized the lesion, lest reconfirmation of the level is needed. It is after I have begun the resection of the lesion that I remove the spinal needles. The thoracic spine can be a lonely region if you find yourself at the wrong level. A meticulous, systematic and redundant approach minimizes, but never eliminates, such risk.

Exposure

With the level confirmed, I plan the incision 3.0 cm off the midline for a total length of 3.0 cm. My target for this procedure is the T9 transverse process, which provides me with a reliable corridor to both the lateral aspect of the central canal and the pedicle. As will be shown in Chapter 11, Minimally Invasive Resection of Intradural Extramedullary Lesions within the Thoracic Spine, there is a unique topography to the thoracic spine compared to the lumbar spine. The thoracic transverse process projects in the posterior plane, whereas the lumbar transverse process projects in the lateral plane. The posterior projection of this bony prominence makes it an ideal target for dilatation (▶ Fig. 10.7).

After making the incision with a No.15 blade and opening the fascia with cautery, I carefully pass the first dilator onto the T9 vertebra. In metastatic disease of the spine, I have encountered circumstances where the dilator finds its way quite easily through the diseased bone. I prefer to palpate the transverse process directly and assess the stability of that bony prominence before dilating over the top of it. If I do not appreciate solid intact bone, I shift my position onto such a surface that I know for certain can withstand the downward pressure of dilatation. For successful dilatation and positioning of the minimal access port, intact lamina, facet or transverse process is essential. I confirm my docking position purely by sounding the anatomy with the first dilator. There is an unmistakable feeling of the tip of the dilator interfacing with the intact bone that you become familiar with in your minimally invasive experience in the lumbar and cervical spine. In this particular circumstance, the transverse process was intact and a suitable target to dilate onto for positioning the retractor.

With the minimal access port in position, I bring in the operating microscope and begin the exposure. Again, I am cautious with my use of the cautery. With a suction in one hand, I curiously and cautiously probe the surface of the bone to ensure its integrity before the tip of the cautery dares brush away the muscle. A transverse process, facet or lamina riddled with metastatic disease has the potential to melt away under the tip of the cautery. Keeping this in mind, I use short bursts of cautery until I achieve direct visualization, and tactile feedback instills in me the confidence that the bone is intact.

I embrace the principle of working from known normal anatomy to uncertain abnormal anatomy, just as I would if I were performing a revision operation. My goal is to expose a perimeter of intact lamina, facet and transverse process either above or below the affected area. At the same time, I make every effort to identify those areas weakened by metastatic disease and remain aware of the vulnerable spinal cord that lies beneath these areas. A careful review of the axial T1-weighted MRI with gadolinium guides me to locate the lesion (▶ Fig. 10.3). In this case, I identified and exposed intact bone on the lamina of T8 and intentionally avoided the T9 lamina, given its appearance on MRI.

Decompression

As I begin my decompression, my first objective is to identify the dura of the spinal cord in a region where there is no compression (Video 10.1). The compression on the spinal cord at T9 originates from the lateral structures, specifically the lamina, pedicle and transverse process. My intention is to identify the spinal cord in the midline above the lesion and work down toward the lesion. With the spinal cord and the metastatic lesion in full view, I extend the decompression into the lateral recess before finally addressing the pedicle.

I begin with a laminectomy at T8, where I know I will find unaffected spinal cord. As demonstrated in the operative video, I drill down the lamina of T8 to the level of the ligamentum flavum and then resect the ligamentum (Video 10.1). I now have full visualization of the spinal cord in the midline. Working from rostral to caudal, I establish a plane between the dura of the spinal cord and the lesion with a right-angled, ball-tipped probe. With the plane established, I begin to resect the lamina of T9 with a forward-angled curet or Kerrison punch and continue working until the central canal has been cleared of metastatic disease. Because of the disease within the bone, a drill may be more of a liability than an asset for this component of the decompression. Once I have completed the preliminary decompression of the central canal, I work my way laterally.

After visual inspection demonstrates the absence of any further compression of the spinal cord from the tumor within the vertebral body, the area may be sealed off with bone wax or another hemostatic agent. As I am performing this component of the procedure, I always keep in mind that what I am doing is palliative. By no means is it intended to be curative. As mentioned at the beginning of this chapter, long-term survival is more a product of primary malignancy type and response to adjuvant therapy rather than from cytoreductive surgery on the spine. This patient has widely metastatic disease throughout the spine. Removing every last cell of the tumor within the vertebral body makes no difference in survival. On the other hand, if I remove too much of the vertebral body, I run the risk of making this segment unstable and in need of further surgery. The goal of the operation was the preservation of neurologic function, with the expectation that this intervention would improve the patient’s quality of life. Separation of the tumor from the spinal cord with subsequent stereotactic radiosurgery, as reported by Laufer et al,8 offers local disease control.

Upon completion of the decompression, I spend a great deal of time working on hemostasis. I cover all of the bleeding bone surfaces generously with bone wax and spend a great deal of time cauterizing the soft tissues. Resection of metastatic disease to the spine is the one circumstance in minimally invasive approaches where I routinely use a drain. I tunnel out a single limb of a Hemovac drain (Zimmer Technology, Inc., Warsaw, IN) and begin the closure in a multilayer fashion.

Postoperative Course

The patient recovered well from both the cervical corpectomy and fusion and the thoracic decompression. The drain was removed on the first postoperative day. The postoperative MRI demonstrated complete decompression of the spinal cord (▶ Fig. 10.8). By postoperative day 2, the patient was ambulating independently with the resolution of urinary retention symptoms and marked improvement in his gait. He was discharged on postoperative day 2 and began radiation therapy of the cervical, thoracic and lumbar spine on postoperative day 5. He completed radiation therapy and continued with chemotherapy without any wound healing issues. The patient succumbed to the progression of metastatic disease 16 months after his initial diagnosis. He maintained bowel and bladder function as well as ambulatory status until he entered hospice care 15 months after his diagnosis.

Related posts:

Minimally Invasive Posterior Cervical Laminectomy Minimally Invasive Far Lateral Microdiscectomy Minimally Invasive Resection of Intradural Extramedullary Lesions within the Thoracic Spine Minimally Invasive Lateral Transpsoas Interbody Lumbar Fusion Anterior Cervical Discectomy with Arthroplasty or Fusion Minimally Invasive Transforaminal Lumbar Interbody Fusion

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