Advances in Minimally Invasive Surgery for Spine Tumors

45 Advances in Minimally Invasive Surgery for Spine Tumors


A. Karim Ahmed, Alp Yurter, Patricia Zadnik Sullivan, Daniel M. Sciubba, and Rory Goodwin


Abstract


Minimally invasive approaches for metastatic spine disease may reduce the recovery time and morbidity for affected patients. As such, accelerated recovery can facilitate earlier adjuvant therapy and serve as a less invasive option for patients with poor prognosis. Two common minimally invasive spine surgery (MIS) techniques for metastatic spine disease include video-assisted thoracoscopic surgery (VATS) and minimal access spine surgery (MASS). Percutaneous pedicle screw fixation (PPSF) is employed in both techniques. VATS allows for access of the anterior column to treat spinal pathologies located from T1 to L2. MASS, with a greater ease of application, has surpassed VATS in popularity and may be applied from T2–S1. Despite the potential benefits, surgeons should be aware of drawbacks in minimally invasive approaches for spine metastases. MIS techniques have limited utility for circumferential tumors and may increase the risk of postoperative epidural hematoma in highly vascular tumors. Moreover, the benefits, indications, and drawbacks should be taken into consideration on an individual basis to make the best decision in treating patients with metastatic spine disease.


Keywords: spine tumor, minimally invasive spine surgery, MIS, metastatic spine disease


45.1 Introduction


In the United States alone, approximately 1.7 million new cases of cancer were diagnosed in 2013,1 with over 500,000 deaths resulting from metastatic disease.2 Advances in diagnostics and therapies have extended patient survival, resulting in a greater incidence of long-term complications. Metastatic epidural spinal cord compression (MESCC), one such example, occurs in 5 to 10% of cancer patients and often requires operative management.3


Surgical management of spinal metastasis is increasingly becoming minimally invasive in nature, in order to reduce tissue damage and the incidence of subsequent morbidities associated with open surgery. Fast recovery time is critical for metastatic spine disease patients, as it reduces the period between surgery and a postoperative adjuvant therapy regimen.4,5,6 Moreover, minimally invasive approaches offer patients with poorer health status (i.e., high systemic tumor burden, aggressive tumor pathology, short expected survival [< 6–12 months], and old age) a less morbid surgical procedure.7,8,9 The two prominent minimally invasive surgery (MIS) techniques used to treat metastatic spine disease are endoscopic video-assisted thoracoscopic surgery (VATS) and mini-open surgery, also known as minimal access spine surgery (MASS).10 These procedures are often used with percutaneous pedicle screw fixation (PPSF) to stabilize the vertebral column.


This chapter will review the following MIS techniques for spinal metastasis: PPSF, endoscopy VATS, and mini-open decompression/MASS.11,12,13 Preoperative planning, instrumentation, surgical approach and techniques, and patient case examples are discussed.


45.2 Evolution of Techniques


45.2.1 Percutaneous Pedicle Screw Fixation


Percutaneous Schanz screws inserted into the pedicles with an external spinal fixation system were first described and popularized by Magerl.14 Since then, image guidance systems (CT and, later, fluoroscopy) have been developed to facilitate percutaneous pedicle screw placement and PPSF has been used to treat numerous spine pathologies, including metastatic spine disease.15


45.2.2 Video-Assisted Thoracoscopic Surgery


VATS was developed in order to reduce approach-related morbidity associated with traditional transthoracic approaches.5 While standard thoracotomy provides excellent access to the anterior spine with minimal manipulation of the spinal cord, major surgical complications can ensue, leading to increased length of stay (LOS), mortality, and resource utilization.16,17,18 Moreover, in elderly patients (≥ 65 years) the risk of complications for open thoracotomy exceeds the benefits of operative treatment.19 VATS was adapted from the field of cardiothoracic surgery, in which patients exhibited reduced recovery time, shorter hospital LOS, and decreased morbidity.20,21,22 This technique was first used in 1993 to treat spinal disorders22 (e.g., discectomy for herniated discs, abscess drainage, anterior release for kyphoscoliosis, etc.), but it was not until 1996 that anterior spinal decompression and stabilization was performed via VATS in patients with metastatic spine disease.16 Currently, VATS can approach the spine anteriorly and laterally from either side and treat levels T1–T12 as well as L1–L2.23


45.2.3 Mini-open Decompression/Minimal Access Spine Surgery


MASS was first reported in 1997 as an approach for anterior lumbar fusion in the context of spinal trauma and degeneration.24 Initially, it was used for spinal levels L2–S1, but has since evolved to allow accessibility of T2–S1 using combined mini-open thoracotomy and/or retroperitoneal mini-approach.24,25,26 MASS has surpassed VATS in popularity because of its advantages including ease of application to a wide variety of pathology.


45.3 Advantages and Disadvantages of Minimally Invasive Surgery


MIS allows for faster recovery time and reduces the period between surgery and a postoperative adjuvant therapy regimen. This is crucial for metastatic cancer patients. In addition, minimally invasive approaches can treat a certain subset of patients with poorer health status who would otherwise be precluded from traditional surgical techniques.7,8,9 For example, VATS approaches reduce lung tissue trauma, and PPSF allows retention of the fascial plane, reducing the likelihood of skin breakdown. Overall analgesic use, pain and discomfort, and hospital LOS are lower with MIS.27 In a 2011 meta-analysis, Molina et al26 found that MIS offered decreased blood loss, shorter operative time, and lower complication rates relative to standard open spine surgery when performed by a trained surgeon with experience in MIS techniques.


Current MIS techniques generally have a limited use for circumferential tumors, which are better decompressed with an open approach. Additionally, in the context of highly vascular tumors, MIS decompression techniques can increase the risk of postoperative epidural hematoma, as proper hemostasis may be difficult to achieve in the limited working corridors.11


45.3.1 Percutaneous Pedicle Screw Fixation


PPSF provides biomechanical stability in patients with metastatic disease who have particularly high disease burden or do not require operative decompression and/or anterior column restoration.5 PPSF is also used in conjunction with decompression to stabilize the spine after tumor resection. In circumventing the traditional open approach, muscular denervation, increased intramuscular pressure, ischemia, necrosis, and subsequent muscle atrophy and scarring can be significantly minimized if not avoided.28 Thus, modern percutaneous screw instrumentation allows for quick stabilization, minimal soft-tissue exposure, and a reduced soft-tissue healing duration.5 The less invasive exposure decreases the risk of infection.29 Additionally, the benign nature of the procedure allows for subsequent radiosurgery or earlier adjuvant radiation.5


This technique may initially have a steep learning curve, as it requires safe, accurate placement of instrumentation and access to intraoperative fluoroscopy. Moreover, PPSF in the upper thoracic spine can be technically difficult due to the small pedicle sizes. Preoperative CT scans and anteroposterior (AP) radiographs must be carefully examined to determine whether pedicles can be cannulated. Additionally, at the L5/S1 level, percutaneous retraction sleeves may impinge upon each other at the skin level.28 Finally, PPSF is not as secure as standard pedicle screw fixation, and this fact should be accounted for when selecting patients.


45.3.2 Video-Assisted Thoracoscopic Surgery


VATS allows for the visualization and magnification of the entire thoracic ventral spine (T1–T12), and permits the decompression, reconstruction, and stabilization of the spine.10 The magnitude of superficial incisions, muscle dissection, and rib retraction is less than that of open thoracotomy.30 Consequently, this technique provides shorter recovery time and decreased hospital LOS, as well as decreased approach-related and thoracotomy-associated morbidities in comparison to open thoracotomy, while providing comparable exposure for thoracic corpectomy and anterior column stabilization.5,20,21,22,30 In particular, the risk of postoperative pulmonary morbidity, scapular dysfunction, intercostal neuralgia, and hindered chest wall movement is reduced.10 Further, some surgeons find that this technique provides superior access to extreme ends of the thoracic cavity (e.g., T3–T4) as it circumvents the need to mobilize the scapula and transect the rhomboid muscles.30 Finally, VATS allows two surgeons to work in tandem as well as providing visualization to the entire team.


However, there are notable drawbacks to VATS: a steep learning curve, the need for specialized training, and expensive equipment.10,26 There is a need for single-lung ventilation for sufficient visualization of anatomical structures. Furthermore, as with open thoracotomy, posterior spinal structures cannot be accessed and the contralateral pedicle can only be exposed in a limited fashion. As such, posterior approaches may be more suitable than VATS for patients who require circumferential decompression or have significant deformity. Finally, the management of intraoperative complications such as hemorrhage and dural tears may be difficult and may require the adoption of an open thoracotomy.30


45.3.3 Mini-open Decompression/Minimal Access Spine Surgery


In comparison to VATS, MASS is easier to learn, involves a more familiar exposure for most spine surgeons, facilitates a faster spinal cord decompression, permits safer mobilization of neurovascular structures, and allows easier reconstruction of the anterior column since spinal elements are visualized in three dimensions.13,26 Due to the high degree of visualization, hemostasis is typically easily achieved and the risk for postoperative hematoma is low.11 Various posterior and anterior approaches to the spine can be undertaken using MASS, making it a versatile technique. Because of these advantages, MASS is the standard means of MIS resection for metastasis.10


However, for MASS techniques, intraoperative fluoroscopy is required to ensure the correct level, and dural closure may be difficult through a tube.31


45.4 Indications and Contraindications


Surgery for metastatic spine disease is suited for those with mechanical instability, radioresistant tumors, medically intractable pain, and/or progressive neurological deficits resulting from spinal cord compression, given that they have sufficient life expectancy and health status.32 For open surgeries, literature recommends that patients have an expected survival of at least 3 months, which is determined by a multidisciplinary team of medical and radiation oncologists as well as the surgical teams.33 In general, MIS techniques are indicated for candidates with less favorable characteristics, including high systemic tumor burden, aggressive tumor type, shorter expected survival (< 6–12 months), and old age.7,8,9 MIS surgical candidates should be unqualified (i.e., have restrictive comorbidities or have failed alternative therapies) for more aggressive treatments.8


MIS approaches are typically contraindicated for circumferential tumors that require an open approach for adequate decompression and highly vascular tumors for which proper hemostasis can only be confidently achieved with an open approach.11 Moreover, because MIS techniques involve partial resection, they have limited applications to solitary metastasis, which may benefit more from en bloc resection.10


45.4.1 Percutaneous Pedicle Screw Fixation


Stand-alone PPSF may be appropriate for mechanically unstable patients who are unsuited for cement augmentation procedures (vertebroplasty/kyphoplasty) and who have disease burden that prevents them from undergoing open surgery.5,34 PPSF may be combined with other MIS techniques given that there are no contraindications (see the following discussion).


However, patients with major spinal instability (e.g., absence of anterior column support) are contraindicated for stand-alone MIS posterior instrumentation without anterior column augmentation (e.g., cage insertion, methylmethacrylate augmentation, concurrent vertebroplasty/kyphoplasty), as MIS instrumentation is currently not as strong as that used in open surgeries.11


45.4.2 Video-Assisted Thoracoscopic Surgery


VATS is typically indicated in patients who would otherwise undergo open thoracotomy for metastasis, and especially for those who do not have the health status to tolerate the more invasive option. Most spinal lesions requiring surgery using an anterior approach can be treated with VATS.23


However, VATS is unsuitable for patients with the following comorbidities: pleural adhesions (e.g., from prior chest surgery, infection, or trauma) and pulmonary conditions that make single-lung ventilation dangerous (e.g., asthma or chronic obstructive pulmonary disease).30 Moreover, because hemorrhaging is difficult to manage with VATS, surgeons should consider the alternative option in cases of highly vascular tumors; excessive bleeding can hinder visualization and compromise safety. Some surgeons forgo VATS entirely for metastatic spinal malignancies to avoid the risk of tumor dissemination to trocar insertion sites.23


45.4.3 Mini-open Decompression/Minimal Access Spine Surgery


Currently, MASS is the standard minimally invasive surgical technique for decompressing and reconstructing the spine. General indications for this technique are those mentioned at the beginning of this section. However, relative contraindications include tumor involvement at two or more levels, certain hemorrhagic tumors, and morbid obesity because the height of the tube may be too short.31


45.5 Preoperative Planning


In general, patients with MESCC should be started on a corticosteroid regimen.35 Vascular metastatic lesions should be considered for preoperative angiogram and embolization.36 Standard images (MRI, CT, AP radiographs) should be taken to identify the levels of tumor pathology. Patients should undergo standard neurological examination to determine the severity of neurological deficits.


45.5.1 Percutaneous Pedicle Screw Fixation


Prior to PPSF, the surgeon should carefully evaluate preoperative CT scans and AP radiographs to determine whether the pedicle can be cannulated. This is particularly relevant for the mid-upper thoracic spine, at which pedicles are small, and T1–T4 levels, at which pedicle angulation changes. Pedicles should be confirmed to have a width of at least 3 to 4 mm to ensure adequate Jamshidi needle navigation.28


If there is an option to choose a specific imaging modality (CT vs. three-dimensional [3D] fluoroscopy vs. standard 2D fluoroscopy), one should weigh the benefits of pedicle screw placement accuracy against the time required to acquire data; while CT navigation has been shown to be more accurate than other modalities, it requires pre- and intraoperative preparatory steps that are not present in fluoroscopic imaging.37,38 Because fluoroscopy avoids time-consuming steps inherent to CT systems without sacrificing too much accuracy, it is the conventional means of navigation.39 For fluoroscopy, two units should be placed to enable lateral and AP views.


45.5.2 Video-Assisted Thoracoscopic Surgery


Standard preoperative spine imaging should be supplemented with radiographic assessment of the posteroanterior and lateral chest to determine potential pleural fluid, fibrinous membranes, or pleural adhesions.23 The presence of such conditions significantly increases the need to convert to an open procedure.27 Because VATS requires single-lung ventilation, patients with a history of smoking and chronic obstructive airway disease require preoperative pulmonary function tests, arterial blood gas evaluation, and cessation of smoking prior to surgery.27


45.5.3 Mini-open Decompression/Minimal Access Spine Surgery


Based on the preoperative images, a trajectory should be chosen to access the tumor. There should also be a plan to convert to an open procedure in the event of major intraoperative complications.


45.5.4 Instrumentation Notes


Percutaneous Pedicle Screw Fixation

Imaging requires equipment for fluoroscopy or CT scanners with stereotactic navigation. Cannulated awls are required for pedicle cannulation. Guidewires and cannulated taps assist pedicle screw trajectory. Rods, screws, and screwdrivers/reduction towers are used in the final stages of the procedure to stabilize the spine.11


Video-Assisted Thoracoscopic Surgery

VATS requires a video endoscope, C-arm fluoroscopy, and video monitors for visualization. A double-lumen endotracheal tube is necessary to collapse the lung at the side of metastasis. A trocar is needed as a conduit for endoscope insertion.


Mini-open Decompression/Minimal Access Spine Surgery

Unique to MASS is the use of a table-mounted retractor system or tubular retractor (either expandable or nonexpendable) for exposure to the site of disease. Additionally, fluoroscopy is used to identify the level of the lesion.


45.6 Surgical Approach


45.6.1 Percutaneous Pedicle Screw Fixation


Patients with metastatic spine tumors often have multiple adjacent vertebral bodies affected by disease. In patients undergoing PPSF for local deformity or instability due to metastatic spine disease, the offending level should be identified and bilateral pedicle screw fixation is recommended two to three levels above and below the level of interest to provide multiple sites of fixation.11


45.6.2 Video-Assisted Thoracoscopic Surgery


In patients with previous lung surgery, surgical approaches on the affected side may be limited by pleural adhesions.


45.6.3 Mini-open Thoracotomy


For tumors of the upper thoracic spine, a right-sided approach is recommended to avoid the thoracic duct. For tumors of the thoracolumbar region, the left-sided approach is recommended to avoid direct trauma to the vena cava.


45.6.4 Surgical Technique


Percutaneous Pedicle Screw Fixation

The patient is placed prone on the operating table, and biplanar fluoroscopy or an intraoperative CT scanner with navigation is used to localize the level of pathology and any relevant surgical landmarks. Individual paraspinal stab incisions are made for each of the pedicle screw entry sites. Alternatively, a midline incision may be made through the soft tissue to the dorsal interfascial plane. Individual stab incisions off midline may then be made through the interfascial plane for pedicle instrumentation (image Fig. 45.1). Preservation of the fascial plane is crucial for expedited wound healing, particularly in metastatic cancer patients who are likely to undergo postoperative radiation therapy or chemotherapy.


A cannulated awl and taps are used under the guidance of fluoroscopy or intraoperative navigation to create the trajectory for the pedicle screws. A guidewire is then placed in the cannula and pedicle screws are placed over the guidewires. Guidewires are then removed. An additional stab incision is made for the introduction of the rod and the screws are locked into place. The wound is irrigated and closed using multilayer closure.


In order to reduce operating time, when performing multilevel fixation, rod insertion should be carefully planned out. Rod length should be determined, and the length between the retraction sleeves can help in determining this. Whether the rod requires bending or needs an additional incision for insertion, and from which end the rod should be inserted should be determined prior to insertion.28


Oct 17, 2019 | Posted by in NEUROSURGERY | Comments Off on Advances in Minimally Invasive Surgery for Spine Tumors
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