Hybrid Therapy for Metastatic Epidural Spinal Cord Compression: Technique for Separation Surgery and Spine Radiosurgery

Abstract

Background: Despite major advances in radiation and systemic treatments, surgery remains a critical step in the multidisciplinary treatment of metastatic spinal cord tumors.

Objective: To describe the indications, rationale, and technique of "hybrid therapy" (separation surgery and concomitant spine stereotactic radiosurgery [SRS]) along with practical nuances.

Methods: Separation surgery describes a posterolateral approach for circumferential epidural decompression and stabilization. The goal is to decompress the spinal cord, stabilize the spine, and create adequate separation between the neural elements and the tumor for SRS to achieve durable tumor control.

Results: A transpedicular route to achieve ventrolateral access and limited resection of the tumorous vertebral body is carried out. In the setting of high-grade cord compression, caution must be taken when performing the tumor decompression. "Separation" of the ventral epidural tumor component anteriorly creates space for concomitant SRS while a simple laminectomy would not adequately achieve this goal. Dissection of the posterior longitudinal ligament allows maximal ventral decompression. Gross total tumor resection is not crucial for durable tumor control using the "hybrid therapy" model. Thus, attempts at ventral tumor resection may unnecessarily increase operative morbidity. Cement augmentation of the construct or vertebral body may improve construct stability. CT myelogram is the preferred exam for postoperative SRS planning. Radiosurgical planning constitutes a multidisciplinary effort and guidelines for contouring in the postoperative setting have recently become available.

Conclusion: Separation surgery is an effective, well-tolerated, and reproducible surgery. It provides safe margins for concomitant SRS. Combined, this "Hybrid Therapy" allows durable local control, maintenance of spinal stability, and palliation of symptoms, while minimizing operative morbidity.

Keywords: Hybrid therapy; Radiosurgery; Separation Surgery; Tumor.

FIGURE 1.

Illustration of the thoracic spine. A, Pedicle screws and connecting rods have been inserted two levels above and two levels below the tumor level. B, The outlined area represents the decompression margins. Note that pedicles and joints are drilled bilaterally to the level of the vertebral body. © 2018 Department of Neurosurgery, Memorial Sloan Kettering Cancer Center. Used with permission.

FIGURE 2.

Dissecting the tumor off of the dura. It is imperative to find normal dural margins, locate a plane between the tumor and the dura and then continue removal of the tumor. © 2018 Department of Neurosurgery, Memorial Sloan Kettering Cancer Center. Used with permission.

FIGURE 3.

Once the posterior part of the tumor has been removed and the dura and exiting nerve roots are exposed, a ventral plane between the tumor and the thecal sac is located. The tumor is pushed ventrally off of the thecal sac. © 2018 Department of Neurosurgery, Memorial Sloan Kettering Cancer Center. Used with permission.

FIGURE 4.

Resection of the posterior longitudinal ligament allows assurance of adequate ventral decompression. Residual tumor ventral to the thecal sac is then further compressed ventrally creating a safe distance from the thecal sac. © 2018 Department of Neurosurgery, Memorial Sloan Kettering Cancer Center. Used with permission.

FIGURE 5.

Intraoperative ultrasound demonstrating circumferential decompression and reconstitution of the thecal sac.

FIGURE 6.

Representative case example. A 76-yr-old male with renal cell carcinoma presented with severe back pain and no signs of myelopathy. Evaluation including spinal imaging demonstrated a T4 tumor with high grade cord compression. A, and B, Pre and postoperative sagittal imaging. A, Preoperative MRI T2 demonstrating a T4 tumor. B, Postoperative CT myelography demonstrating the surgical and reconstituted thecal sac. C and D, Pre and postoperative axial imaging. C, Preoperative MRI T1 with contrast enhancement. D, Postoperative CT myelography. Note the high-grade cord compression preoperatively and the cerebrospinal fluid-filled thecal sac postoperatively. This new distance between the tumor and the spinal cord allows for safe concurrent radiosurgical treatment.

FIGURE 7.

Postoperative CT myelography at T4 demonstrating contouring for the patient described in Figure 6. Contouring of the GTV in the postoperative setting is done using preoperative imaging and the CTV is delineated accordingly. OARs are outlined fusing preoperative to postoperative CT myelogram or MR scans. The CTV includes abnormal marrow signal suspicious for microscopic invasion and an adjacent normal bony expansion to account for subclinical tumor spread in the marrow space. To note, in the case presented, a small space posterior to the dura (orange) is outlined as a P32 brachytherapy plaque was placed on the dura during surgery delivering radiation to the posterior dural margin intraoperatively and allowing for optimal dose delivery postoperatively.^,A, The GTV is outlined in red. B, The G = CTV is outlined in green. C, The PTV is outlined in blue. The OARs are outlined as follows; esophagus in purple, spinal cord in light green, dura in yellow. OARs = organs at risk, GTV = gross tumor volume, CTV = clinical target volume, PTV = planning target volume.