Thoracolumbar Metastatic Tumors: Comparison of Minimally Invasive Surgery versus Open Techniques for Addressing Thoracolumbar Metastatic Tumor Resection and Stabilization

18 Thoracolumbar Metastatic Tumors: Comparison of Minimally Invasive Surgery versus Open Techniques for Addressing Thoracolumbar Metastatic Tumor Resection and Stabilization

MIS: Prashanth J. Rao and Ralph J. Mobbs
Open: Peter S. Rose and Michelle J. Clarke

18.1 Introduction

Cancer is currently the second leading cause of death in the United States, Australia, and most western nations; it is already the leading cause of death in some developed countries. The majority of patients with cancer have spinal metastases present at autopsy,1,2 with around 30% of them exhibiting symptomatic metastatic spinal disease.³ While only a minority (10%) of these progress to epidural spinal cord, conus medullaris, or cauda equina compression, because of the large numbers involved, metastatic compression of the neural elements is a common occurrence in clinical practice.³ In most estimates, oncologic neurologic compression along the spinal axis is approximately twice as common as traumatic spinal cord injuries.

Radiotherapy is used in the treatment of almost all patients with symptomatic spinal metastases. While the response of any given lesion to radiotherapy is not known, estimates of radiosensitivity can be made based on histology ( Table 18.1). However, radiation therapy is not able to restore mechanical integrity to a spine compromised by pathologic fracture or impending instability. As well, once neurologic signs are present, level I evidence has demonstrated the superiority of direct decompressive surgery followed by radiotherapy to radiotherapy alone in the care of patients with common metastatic histologies.⁴ Clinical experience and published data have shown a benefit for direct decompressive treatment of the spinal cord rather than stabilization alone and/or indirect decompression by laminectomy.

Patients undergoing decompression and stabilization procedures for metastatic spinal cord compression have traditionally been approached in an open manner. However, advances in instrumentation, imaging, and navigation now make minimally invasive approaches possible. These techniques most commonly involve the use of percutaneously placed pedicle screw instrumentation along with decompression through a limited open or tubular retractor system.⁵

18.2 Indications for Surgery for Metastatic Epidural Neurologic Compression

Patients who present with or have impending spinal instability and/or neurologic deficit from typical solid organ metastases are considered for surgical treatment. Patients with hematopoietic malignancies and certain highly chemo- or radiosensitive solid organ metastases (e.g., lymphoma, germ cell tumors) can often be managed without surgical intervention because of the ability to achieve rapid disease regression and decompression of neural elements with these modalities. Patients who have widely disseminated disease with an anticipated life expectancy less than 3 months or multiple sites of spinal involvement seldom benefit from aggressive surgical intervention. Additionally, once a dense neurologic deficit is present, particularly for greater than 48 hours, the likelihood of meaningful recovery is low and surgery is generally not indicated. Surgeons must also evaluate potential surgical patients for their fitness to undergo surgical procedures (particularly if a patient is in the process of receiving chemotherapy at the time of presentation).

Table 18.1 Radiosensitivity of common metastatic histologies

	Histology	Value of radiation as sole treatment
Highly radiosensitive	Myeloma	Effective treatment
	Lymphoma
	Germ cell tumors
Moderately radiosensitive	Breast cancer
Moderately radiosensitive	Small cell lung cancer
Moderately radioresistant	Colon cancer
Moderately radioresistant	Non–small cell lung cancer
Highly radioresistant	Renal cell carcinoma
	Thyroid carcinoma	Suboptimal/Unreliable treatment
	Sarcoma
	Melanoma

Several clinical scales have been introduced to guide the treatment of patients with metastatic disease to the spine. The Spinal Instability Neoplastic Score (SINS) from the Spine Oncology Study Group is the most contemporary method to evaluate for present or potential spinal instability from neoplastic processes.6 While a number of clinical scoring systems exist to stratify patients for aggressive, palliative, or nonoperative treatment, the modified Tokuhashi score is currently the most widely accepted treatment framework in clinical practice.⁷ It assesses the patient’s spinal and extraspinal disease burden, histology, neurologic status, and performance status to guide treatment recommendations.

18.3 Advantages of Minimally Invasive Surgery

The surgical treatment for the majority of patients with metastatic epidural neurologic compression is palliative, while a cure can be achieved in only a minority of select patients with surgically resectable or chemoradiotherapy sensitive disease.8,9 Due to the poor general condition of these patients, open spinal decompression with stabilization surgery may be associated with high morbidity rates.^8,10,11 Basic principles of a minimally invasive surgery (MIS) approach in spine surgery include the following: (1) avoid iatrogenic muscle injury by self-retaining retractors; (2) do not disrupt tendon attachment sites of key muscles, particularly the origin of the multifidus muscle on the spinous process; (3) use known anatomic neurovascular and muscle compartment planes; and (4) minimize collateral soft-tissue injury by limiting the width of the surgical corridor.¹²

There are several important advantages of MIS techniques for spinal decompression and stabilization in metastatic spine disease. Although complete tumor resection through an MIS access could be a limitation, the goal of surgery (open or MIS) in these cases is tumor debulking, neuronal decompression, and mechanical stabilization, which can be achieved readily via an MIS technique. Definitive treatment in such cases is in fact chemoradiotherapy, which can be started earlier in MIS patients given that wound and general recovery are quicker. Although circumferential compression is common, the majority of the metastatic disease is in the vertebral body. A common MIS approach is posterior for spinal metastatic disease; however, anterior or lateral approaches are available to be utilized as either a stand-alone or combined with percutaneous posterior pedicle screw stabilization. Another advantage of the MIS technique is faster wound healing, which lessens the risk of wound dehiscence following radiotherapy. It is common knowledge that prolonged operative time is associated with increased infection rates and elevated blood loss, and blood transfusion is associated with risk of systemic infection, gastrointestinal complaints, and hemolytic reactions.¹³ Due to the minimization of surgical exposure, MIS techniques result in reduced blood loss. Although the criticism of MIS technique is longer operative times, as a result of minimal wound exposure, the operative time is in fact reduced.^14,15 The morbidity of spine surgery in patients with neuronal compression from metastatic tumor can be minimized with MIS techniques by reducing operative time, blood loss, and iatrogenic muscle injury, and decreasing the need for blood transfusions.

18.4 Advantages of Open Surgery

Although some cases are selected for an anterior approach, the majority of patients are approached with a midline posterior approach using pedicle screw stabilization above and below the level of the pathology and a transpedicular or limited costotransversectomy for decompression of the neural elements. When possible, a cage or methylmethacrylate is used to reconstruct the anterior column.

The open technique for stabilization and decompression has several advantages. It is the only technique for which level I evidence supports the surgical treatment of patients with metastatic epidural spinal cord compression. A key aspect in studies that have demonstrated a benefit to surgery in these patients has been the ability to perform a direct decompression of the neural elements. Metastatic tumors leading to cord compression arise in the vertebral body in approximately 85% of cases but commonly demonstrate near circumferential involvement of the spinal canal. Depending on the local anatomy of the tumor, it can be difficult for surgeons to fully access the spinal canal and perform a true direct decompression of the neural elements with MIS techniques. The majority of tumors leading to metastatic spinal cord compression are lytic; an open technique affords the surgeon the widest array of options for reconstruction of the anterior column through a transpedicular or limited costotransversectomy approach. These cases often present in an urgent clinical fashion, and open techniques employ standard spinal instruments, instrumentation, and imaging capabilities that are readily available even when cases are performed on an unscheduled or “add-on” basis.

The techniques of the open approach are an adaptation of techniques known to qualified spine surgeons and do not require any steep learning curves that MIS techniques may have; they are readily “scalable” to apply to lesions that involve more than a single level of compression and are also applicable along the entire length of the spinal axis. While MIS techniques hold the potential for lower complications and more rapid institution of adjuvant treatments, no high-level evidence demonstrates this to be the case. Even if radiotherapy can theoretically be administered 7 to 10 days earlier with MIS techniques, there is no established clinical benefit to this. The net length of surgical incision used in standard surgeries is often substantially less than the sum of incisions used in an MIS procedure given the need for separate incisions for decompression, placement of each screw, and rod placement.

18.5 Case Illustration

A 58-year-old female patient presented with a 2-month history of back pain. She was a heavy smoker but otherwise had no significant past medical history. X-ray of the chest revealed a lung lesion on the right that on computed tomography (CT) guided biopsy was diagnosed as a large cell carcinoma of the lung. Also on the CT scan, a single metastatic lesion was found at the T9 level. She underwent radiation to the spinal lesion for 2 days and then developed rapidly progressive paraplegia (T10 sensory level, 1/5 MRC [Medical Research Council] grade power in lower limbs). On MRI (whole spine) scan ( Fig. 18.1), circumferential spinal cord compression was identified at the T9 vertebral level due to tumor involving all the three columns. On T2-weighted images ( Fig. 18.1a, d), there was no cerebrospinal fluid evident around the spinal cord at that level. With the administration of contrast ( Fig. 18.1c, e), the tumor was enhancing and involved all the spinal columns including the prevertebral soft tissue.

Fig. 18.1 Preoperative magnetic resonance imaging scan. (a) Sagittal T2-weighted image of cervicothoracic region demonstrating circumferential spinal cord compression by metastatic tumor at T9 level. (b) Sagittal T1-weighted image of cervicothoracic region. (c) Contrast-enhanced sagittal image of cervicothoracic region. (d) Axial T2-weighted image at T9 level demonstrating spinal cord compression. (e) Axial contrast-enhancing image.

Median survival was estimated to be between 6 to 9 months after a discussion with her oncologist. After thorough discussion with the patient, it was decided to proceed with surgery within 12 hours after the onset of paraplegia.

18.6 Surgical Technique in Minimally Invasive Surgery

18.6.1 Step 1: Decompression

After induction of general endotracheal anesthesia patient was positioned prone on a Jackson table with Harbor Bridge. Suitable padding of all pressure areas was done. Image intensifier confirmation of the index level was performed prior to prepping and draping. Local anesthetic 0.25% Marcaine with adrenaline was infiltrated along the incision line. A small 4-cm midline incision was placed at the index level. Subperiosteal muscle dissection was performed to expose the T9 lamina, and facet joints (T8/T9) and Versatrac retractors were placed. A T9 laminectomy was performed with high-speed burr and Kerrison rongeurs. Extradural tumor with ligamentum flavum was removed with pituitary rongeurs to decompress the spinal cord posteriorly ( Fig. 18.2a). Bilateral pediculotomies were performed, and tumor involving the pedicles was removed and the posterior part of the vertebral body reached. Extradural tumor compressing the spinal cord anteriorly and involving the posterior half of the vertebral body was removed with pituitary rongeurs resulting in 360-degree decompression of the spinal cord. Vertebroplasty was performed with methylmethacrylate ( Fig. 18.2b) and after hemostasis the wound was closed in layers.

Fig. 18.2 Minimally invasive surgery technique (decompression). (a) Laminectomy and posterior spinal cord decompression. (b) Transpedicular anterior spinal cord decompression and methylmethacrylate augmented reconstruction. (c) Stabilization with percutaneously inserted pedicle screws and rods. (d) Demonstration of midline and percutaneous pedicle screw wounds.

18.6.2 Step 2: Stabilization

Percutaneous pedicle screws (T7, T8, T10, and T11) were placed under image intensifier guidance. Suitable sized rods were threaded onto screw heads and secured with set screws. ( Fig. 18.2c,d; Fig. 18.3; and Fig. 18.4)

18.7 Surgical Technique in Open Surgery

The patient is positioned prone on a radiolucent frame with fluoroscopy used for initial localization and to verify implant position. A midline incision is used to expose to the transverse processes from T7 to T11 and pedicle screws are placed using the surgeon’s technique of choice (anatomic landmarks are the preference of the author) typically two levels above and two levels below the tumor.

A holding rod is maintained on one side at all times to guard against subluxation. A laminectomy is performed from the pedicles of T8 to the pedicles of T10, and the dural plane is accessed above the level of tumor. Once all dorsal tumor is removed, the pedicle on one side is removed and the plane between the posterior longitudinal ligament (PLL) and the dura is identified (the PLL is a natural anatomic barrier to tumor extension and a reliable landmark in cases not previously manipulated). Tumor coming out of the vertebral body is removed using curettes, rongeurs, and suction curettage. The PLL is sectioned with tenotomy scissors and removed to avoid leaving tumor remnants in close proximity to the neural elements.