Claudio E. Tatsui, Laurence D. Rhines, and Garrett L. Walsh
Introduction
The surgical management of a spinal tumor is complex and is influenced by multiple patient, disease, and surgeon variables. In general, morbidity is directly related with the complexity of the operation and inversely related with postoperative quality of life. Therefore, the treating physician needs to tailor the extension of the surgical intervention for each individual patient to achieve the best balance in quality of life regardless if the goal is cure, long-term disease control, or palliation.
The term en bloc refers to removal of the whole tumor in one piece together with a margin of normal tissue. Histopathologic examination of the surgical specimen classifies the margin as: (a) intralesional:when the surgeon has cut within the tumor, (b) marginal: when the dissection occurs in the reactive interface between tumor and normal tissue, and (c) wide: when the tumor is removed together within a layer of healthy tissue.
En bloc resection of spine tumors should be attempted only when a marginal or a wide margin is possible. It is a technically demanding procedure and requires a highly skilled team of anesthesiologists, spine, thoracic, and plastic surgeons to achieve a good outcome. This chapter describes the surgical technique utilized to perform a single-staged thoracic en bloc spondylectomy.
INDICATIONS
The best indication for an en bloc spondylectomy is the presence of a solitary well-demarcated tumor contained within the periosteal layer of a vertebral body, without extension to the epidural space or paravertebral structures. Such a strict requirement is relatively uncommon in clinical practice, thus limiting the application of this technique to special selected cases of primary spinal tumors, when the goal of surgery is cure. If these conditions are not met, the goal is immediately downgraded to long-term control of the disease, which is acceptable in cases of primary vertebral tumors with partial response to adjuvant treatment and have no gross extravertebral extension or selected cases of solitary spinal metastasis with controlled systemic disease.
We believe this technique should not be applied in cases where a gross total resection is not feasible, or when long-term local control of disease does not affect functional status or survival.
Surgical Staging and Planning
Meticulous preoperative imaging evaluation of the chest, abdomen, and pelvis is required to ascertain that disease is restricted to the vertebral body. Usually MRI with contrast and CT scans are both utilized for this purpose. A CT scan is useful for studying the anatomy of the adjacent pedicles and for planning the extension of the spinal stabilization. An extensive biomechanical analysis is out of the scope of this review, but in general for the nonmobile thoracic spine (T3 to T10), pedicle screw stabilization of two levels above and below the resected level is adequate. When the procedure is performed in junctional levels (T1 to T2 and T11 to T12), we recommend pedicle screw stabilization at least three levels above and below the resected vertebral body.
The thecal sac is surrounded by a bony ring composed by the vertebral body, pedicles, and a posterior arch formed by the laminas and spinous process. To pull the vertebral body away from the contents of the thecal sac, the posterior arch needs to be disconnected from the vertebral body. This requires at least two cuts, which needs to be performed in a bone without tumor. The most useful surgical classification for planning feasibility of an en bloc resection is the Weinstein–Boriani–Biagini classification, commonly referred as the WBB staging. This classification subdivides the vertebra in 12 radiating zones numbered 1 to 12 clockwise and 5 concentric layers labeled A to E from prevertebral to epidural involvement. Ideally for an en bloc resection tumor needs to spare one pedicle (zones 3 to 9, or 4 to 10), and be contained within the vertebral body (layers B, C, and D).
SURGERY
Preparation and Positioning
The procedure is performed from a single posterior midline exposure; it is our routine to have motorization of somatosensory (SSEPs) and motor (MEPs) evoked potentials. We do not monitor electromyography, so the patient can receive paralytics throughout the case. We recommend 10 mg of dexamethasone to be given prior to the skin incision; however, the protective role of high doses of steroids is uncertain. The patient is positioned prone with arms tucked to the side or with arms abducted with the elbows flexed at 90 degrees “superman position,” depending on the level to be removed and the utilization of image guidance or fluoroscopy. Either a Jackson table, or gel rolls in the chest and iliac crest region provide adequate body support and decompression of the abdomen to avoid excessive epidural congestion. It is our preference to place patients in the Mayfield head holder to avoid pressure on the eyes and face during the procedure.
One of the most important factors in such procedure is localization of the accurate level. Since the tumor is contained within normal bony edges, all vertebral bodies will have a relatively normal appearance in the intraoperative fluoroscopy images. We usually use live fluoroscopy in anteroposterior and lateral projections to count pedicles from the bottom (sacrum) to top (level of interest). We always double check the count since performing resection at the wrong level is an unacceptable mistake. Once the level of interest is identified, the skin exposure is marked on the midline, extending at least two spinous processes above and below the tumor.
Exposure
A midline approach is performed and subperiosteal dissection of the paraspinal musculature with monopolar cautery exposes the spinous processes, laminas, and transverse process of at least two levels above and below the resection. Both ribs attached to the pedicle of the level of interest and the level below has to be exposed 10 to 12 cm laterally in the paraspinal region. This additional exposure is needed for resection of the rib heads to allow adequate access to the intervertebral discs and pleural space above and below the tumor. An Allis clamp is placed on the transverse process of the level planned to be resected and the level is again confirmed with AP and lateral fluoroscopic images. If the surgeon is using image guidance, the parameters for the navigation require an intact lamina and spinous process for registration; therefore, this step is performed prior to the laminectomy. We recommend placing the spinal instrumentation at this stage.
Figure 31.1 En bloc removal of the posterior elements. The ligamentum flavum above and below the lamina is removed exposing the epidural space. All soft tissues under the pars interarticularis are dissected and a plastic malleable tube is passed under the lamina from rostral to cudal and medial to lateral. Next a thread wire saw is used to cut the pars with reciprocating movements.
If there is no evidence of tumor infiltration of the spinous process and lamina, a piecemeal resection is perfectly acceptable to expose the dural sac. Complete removal of the interlaminar ligaments and a partial laminectomy of the level above and below is required for adequate access to the intervertebral discs. Alternatively, the posterior elements can be removed in a single piece. This requires stripping the capsular ligaments of facet joints and piecemeal removal of the ligamentum flavum above and below the lamina of interest to expose the epidural space. All soft tissues lateral and under the pars interarticularis are dissected taking extreme care to avoid injury to the underlying dura mater and nerve root. Careful utilization of curved ball-ended or Woodson dissectors allow releasing epidural adhesions and identification of a safe plane. We use a thread wire saw which is passed under the lamina in a rostral-to-caudal and medial-to-lateral orientation. The ideal location of the saw is wrapping around the pedicle at the base of its insertion in the lamina, dorsal to the exiting nerve root. This allows performance of a safe cut with reciprocating movements. Repeating the procedure on the contralateral side releases the posterior elements in one piece (Fig. 31.1).
The epidural veins are cauterized with of bipolar and a small right angle clamp is used to dissect the axilla of the exiting nerve roots. The clamp is passed under the nerve and a. 0 silk suture is used to tie the nerve prior to the spinal ganglion. Sacrificing the nerve root prior to the ganglion avoids neuropathic pain and allows safe mobilization of the thecal sac from the posterior longitudinal ligament without excessive traction on the spinal cord. It is imperative that the dural sac is completely dissected from the posterior longitudinal ligament with a ball-ended dissector or a Penfield no. 3 passed free under the thecal sac from the disc above to the disc below the level of interest. It is very important that any incidental durotomy gets immediately repaired, since maintenance of a full thecal sac helps decrease the mechanical trauma to the spinal cord during manipulation of the dural tube (Fig. 31.2).
Pleural Dissection
The intercostal muscles are detached from the exposed ribs and a right angle clamp or pigtail periosteal dissector is used to dissect the retropleural plane from the undersurface of the rib. This dissection is carried as far medial as possible towards the transverse process. The rib is resected and the bone can be saved as an auto graft. This maneuver is performed bilaterally and is the beginning of the extracavitary approach. Next, if there is no evidence of tumor, the transverse process can be resected exposing the underlying rib head and the costotransverse ligaments. The rib head needs to be completely resected increasing the exposure of the retropleural plane and the posterior-lateral aspect of the vertebral body. From this point, a sponge stick is used to gently peel off the retropleural plane from the vertebral body (Fig. 31.3).
Figure 31.2 This picture demonstrates the complete laminectomy and resection of the supra- and infralaminar ligamentum flavum, exposing the thecal sac. A complete facetectomy was performed above and below the pedicles of interest exposing the nerve roots which were dissected and ligated proximal to the ganglion. The transverse processes of the level of interest were resected and the rib head at the level of interest above and below were removed, exposing the underlying pleura and posterior-lateral aspect of the vertebral body. It is imperative that the dura is completely detached from the posterior longitudinal ligament allowing free passage of a Penfield no. 3 under the thecal sac from the disc above and below the vertebral body of interest.
The segmental vessels lie in the midportion of the lateral aspect of the vertebral body. Very often a branch coming off the segmental vessel to feed the vertebral body is found, and attempt to elevate the segmental will rip this vessel and cause bleeding, usually requiring sacrifice of the segmental for control. Once the anterolateral portion of the vertebral body is reached on both sides, bilateral gentle finger dissection is used to elevate the subpleural plane away from the anterior surface of the vertebral body until both fingertips meet. The surgeon must feel that all retropleural planes are dissected away from the spine above and below the intervertebral discs. This is a critical step and relies completely on tactile feedback. Once dissection is completed, a malleable dissector is bent and passed from one side around the vertebral body to the contralateral side, isolating the retopleural space, to protect the great vessels during disconnection of the anterior annulus and anterior longitudinal ligament (Fig. 31.4).
Figure 31.3 This picture demonstrates the pleura being separated with a sponge from the right and left posterior vertebral body. This is possible after resection of the transverse process and the rib head above and below the level of interest. This pleural dissection usually detaches the segmental vessel from the lateral aspect of the vertebral body. Usually a branch feeding the vertebral body arises from the segmental and needs to be cauterized to proceed anteriorly with the dissection.
Figure 31.4 Once the pleural dissection reaches the anterolateral aspect of the vertebral body, the surgeon uses bilateral finger dissection. This step relies on tactile feedback. Both fingers must meet anteriorly and the retropleural plane needs to be dissected away from the spine extending from above and below the intervertebral discs. Once this dissection is completed a malleable dissector is bent and used to isolate and maintain this plane around the spine.
Temporary Spinal Stabilization and Discectomy
We usually place a temporary rod on one side and work on the contralateral side during this step. This provides stabilization of the spine and allows application of slight distraction, facilitating the mobilization and rotation of the vertebral body when the disconnection is completed. It will also prevent collapse of the vertebral column which could cause damage to the spinal cord (Fig. 31.5).
At this stage, it is imperative that the dural sac is completely free from all lateral and anterior attachments. If a durotomy occurs at any stage of the procedure, we advocate immediate repair. Any retraction on the dural tube is more likely to cause damage to the spinal cord if there is no fluid around the spinal cord to act like a cushion. The assistant gently retracts and elevates the thecal sac to expose the posterior annulus of the intervertebral disc. A no. 15 blade is used to cut the disc annulus as far medial as possible. This maneuver is repeated in the contralateral side until both cuts meet in the midline. The temporary rod is moved from one side to the other during these cuts. Subsequently, pituitary rongeurs are used to perform an aggressive discectomy (Fig. 31.6).
Figure 31.5 This picture demonstrates the temporary rod. Slight distraction of the screws is used to enlarge both disc spaces. Note the pleural plane is isolated by the malleable dissector, which can be mobilized cranial and caudal in front of both intervertebral discs. At this stage, the dura needs to be completely dissected from the adhesions with the posterior vertebral body.
Figure 31.6 This picture demonstrates the assistant gently retracting the thecal sac medially and superiorly and the surgeon performing an incision in the posterior annulus (for better illustration the temporary rod was removed).
Once the posterior annulus is completely cut, the pleura is retracted and incision is extended to the lateral annulus as far anteriorly as possible. Removal of the disc with a pituitary is continued until the anterior annulus is reached. The malleable retractor is positioned in front of the anterior annulus and isolates the pleura and great vessels away from the spine A no. 15 blade is used to complete the cut and disconnect the disc space. Similar technique is used in the other disc space (Fig. 31.7). This maneuver completes the disconnection of the vertebral body, which should be very mobile (Fig. 31.8). Slight increase in the distraction allows easier mobilization and the vertebral body, which is grasped with an Allis or Kocher clamp and carefully rotated away from the thecal sac toward the opposite side of the temporary rod.
Figure 31.7 This picture illustrates the final cut of the anterior annulus which completes the release of the vertebral body. A clamp is used to grasp the pedicle and carefully rotate the vertebral body away from the thecal sac.
Figure 31.8 Photograph showing the specimen after en bloc resection. The tumor is completely contained within the boundaries of the vertebral body.
Reconstruction of the Vertebral Body and Closure
A variety of techniques can be used for the reconstruction of the vertebral body. Since this procedure is performed with the goal of long-term control or cure, an interbody fusion should always be attempted. The residual disc and the cartilaginous end plate are completely removed using curettes and the subchondral bone of vertebral body above and below is exposed. It is our preference to use expandable cages, which are placed carefully from a posterolateral direction. The cage is packed with bone auto or allograft and expanded to reconstruct the height of the resected vertebral bodies and discs. Care needs to be taken to avoid excessive distraction which increases the tension on the thecal sac and can potentially stretch the spinal cord. Also, overdistraction will create a fracture of the end plates and the cage can subside into the adjacent vertebral bodies.
Once the cage is placed, the spinal instrumentation is completed (Fig. 31.9). A crosslink is added and decortication of the laminas and spinous processes is performed. Bone graft is added for a posterolateral arthrodesis.
Figure 31.9 Final picture of the procedure, with the expandable cage in place and the instrumentation locked.
Figure 31.10 Postop CT reconstructions depicting the 360-degree reconstruction after en bloc vertebrectomy.
The wound is closed using a routine multilayered closure or alternatively, plastic surgery can rotate muscle flaps to cover the bony defect if a concern with healing is anticipated. We usually place an epidural drain. If the pleura is violated during the exposure, chest tubes are placed. We keep patients on prophylactic antibiotics until all drains are out.
We usually obtain postoperative x-rays and CT scans with sagittal and coronal reconstructions (Fig. 31.10). Once adequate placement of the instrumentation is confirmed, patients are encouraged to mobilize as soon as possible. We do not routinely use a thoracolumbar orthosis.
CONCLUSION
This chapter describes the technique for a single-staged en bloc vertebrectomy. This procedure is technically demanding and should be part of the armamentarium of a dedicated multidisciplinary team including specially trained spine surgeons, thoracic surgeons, plastic surgeons, and anesthesiologists.