Endoscopic Approaches to Cervical Tumors, Trauma, and Infection

51 Endoscopic Approaches to Cervical Tumors, Trauma, and Infection

Christopher C. Gillis and John O’Toole

51.1 Introduction

As the decreased morbidity of minimal access (minimally invasive surgery, or MIS) approaches is increasingly presented in the literature, the techniques continue to evolve and to be expanded to include approaches to the cervical spine.1 Traditional approaches to the dorsal cervical spine continue to require extensive periosteal stripping of the paraspinal musculature that leads to increased postoperative pain, spasm, and dysfunction that can lead to muscular ischemia and can be persistently disabling in 18 to 60% of patients.^2,3,4,5 Furthermore, preoperative loss of lordosis and long-segment decompressions increase the risk for postoperative sagittal plane deformity,^3,6,7 a complication that frequently prompts instrumented arthrodesis at the time of laminectomy. Employing these extensive posterior fusion techniques increases operative risks, time, and blood loss, exacerbates early postoperative pain, and potentially contributes to adjacent-level degeneration.

To reduce the complication of deformity and avoid fusion after cervical decompression, minimally invasive cervical decompression was described as an adaption of MIS lumbar laminectomy techniques and can be adapted to approach both intradural and extradural lesions in the cervical spine, be they tumor or infection.^8,9,10 Additionally, minimally invasive dorsal cervical foraminotomy is a well-described and practiced technique that can be adapted to decompression of nerve roots in the face of impinging pathology.^2,3,11,12 With respect to trauma, MIS lateral mass screw placement has been described, as well as MIS screw placement for traumatic spondylolisthesis of the axis.^3,5,13 Combining these techniques, a wide variety of traumatic, infectious, or neoplastic pathology in the cervical spine can be approached in an MIS fashion, tailored to the specific case. This chapter discusses the basics of these techniques and how to use them.

51.2 Choice of Patient

51.2.1 Indications

Intradural lesions, extradural lesions, dorsal spinal pathology involving the facet, lamina, lateral mass or any of the posterior elements, pathology along the nerve root, and even more laterally located ventral lesions are all appropriate for a minimally invasive approach. Generally, the MIS approach works best with lesions spanning less than two spinal levels. In cases where fusion is required, such as in trauma, it can be done with MIS lateral mass screws or percutaneous screws.

51.2.2 Contraindications

Generally, lesions spanning more than two spinal segments or tumors with a significant ventral portion are too difficult to approach with MIS techniques, due to the size limitation of the expandable retractor, even with angling of the retractor.^8,9,14,15 Open approaches are often considered in these cases. Tumor and trauma cases that are in the vertebral body in the cervical spine are best approached through anterior approaches, due to the presence of the vertebral artery. The traditional anterior cervical approach takes advantage of natural tissue planes and thus is best for these cases.

51.3 Procedure

The basic tools of MIS in the lumbar spine are adapted to use in the cervical spine. The approaches are performed using muscle dilators and tubular retractors (which can include either fixed or expandable tubular retractors), and visualization can be achieved through use of an endoscope, loupes, and a headlight, or even the operating room microscope. The patient is usually positioned prone; however, the sitting position is an option when performing endoscopic foraminotomy.

51.3.1 Foraminotomy

With prone patient positioning, the head is held with a Mayfield pin holder or Gardner-Wells tongs, with the neck in slight flexion, which allows for rigid holding of the cervical spine during muscle dilation. Also with the prone position, the operating table is tilted in a reverse Trendelenburg position to ensure that the cervical spine is parallel to the floor. For the sitting position, the patient’s head is fixed in a Mayfield head holder. The table is manipulated to place the patient in a semisitting position with the chin flexed and the neck straight and perpendicular to the floor, and the table is turned either 90° or 180° relative to the anesthesiologist.

For foraminotomy, the general approach is paramedian. The operative level(s) and entry point are confirmed on lateral fluoroscopy with a Kirschner (K)-wire or the inner muscle dilator. A 2-cm longitudinal incision is marked out ~ 1.5 cm off the midline on the operative side and is injected with local anesthetic. For two-level procedures, the incision should be placed midway between the targeted levels. Once an optimal trajectory is established, using fluoroscopy as the guide, due to the thicker fascial and muscle attachments in the cervical spine, dissection is taken down to the fascia, which is then incised with a scalpel or electrocautery to accommodate dilators. Metzenbaum scissors are used to bluntly dissect to the level of the facets to enable “force-free” insertion of the tissue dilators. The fascia is retracted, and the smallest dilator is placed through the posterior cervical musculature under fluoroscopic guidance and is docked on the facet at the level of interest. A slightly lateral trajectory is advised to avoid the spinal canal and to ensure contact with the lateral mass. Successive tubular muscle dilators are carefully and gently inserted, remembering that the axial forces that are routinely applied during muscle dilation in the lumbar spine are hazardous in the cervical spine (Fig. 51.1).

Fig. 51.1 Intraoperative view during sitting endoscopic minimally invasive cervical foraminotomy. (a) Paramedian incision in the cervical spine with insertion of the fixed retractor over the dilators. (b) The fixed tubular dilator in the final position after removal of the dilators, affixed to the rigid retractor arm.

After dilation, the final tubular retractor is placed and is secured over the laminofacet junction with a table-mounted flexible retractor arm. The following steps are performed under microscopic magnification or using loupes and headlight or an endoscope attached to the tubular retractor. Tissue is cleared off the bone to expose the underlying lamina and lateral mass using monopolar cautery and a pituitary rongeur, taking care to start and maintain the dissection laterally and over solid bone.

The medial facet/interlaminar space junction is identified. Using a high-speed drill, a partial laminotomy-facetectomy is performed, beginning at the medial facet/interlaminar space and going laterally, removing less than 50% of the facet, to maintain biomechanical integrity. The dorsolateral portion of the superior lamina and the medial part of the inferior articular facet are removed first. This will permit the removal of the lateral corner of the inferior lamina and the medial part of the superior articular facet, exposing the medial border of the caudal pedicle. The nerve root is located directly above the caudal pedicle and anterior to the superior articular facet. The ligamentum flavum can be removed medially after the foraminotomy to expose the lateral edge of the dura and proximal portion of the nerve root. Progressive lateral dissection can then proceed along the root as it enters the foramen. The venous plexus overlying the nerve root should be carefully coagulated with bipolar cautery and incised. With the root well visualized, a fine-angled dissector can be used to palpate ventrally to the nerve root for compressive lesion or tissue. Gentle dissection along the root can allow removal of material ventral and inferior to the root. If there is a large portion of lesion or bony fragment ventral to the root, additional drilling of the superomedial quadrant of the caudal pedicle allows greater access while avoiding the need for excessive nerve root retraction.

51.3.2 Laminectomy/Decompression/Tumor Resection

Laminectomy or decompression is more often done through a laterally to medially oriented approach. A skin incision to accompany the size of retractor desired is made one finger breadth off the dorsal midline, with the incision centered on the level of the disk space. Larger incisions extending over two segments may be necessary for larger lesions and allowing for angulation of the tubular retractor. The operative level(s) and entry point are confirmed with lateral fluoroscopy. The fascia is again incised under direct vision and Metzenbaum scissors used to carry out subfascial dissection down to the level of bone for easy docking of the tubular dilators. Sequential muscle dilation and insertion of the tubular retractor follow, and, again depending on the lesion, an expandable tubular retractor can be placed. The remaining steps are performed under microscopic magnification or using loupes and a headlight or with an attached endoscope. Starting close to the midline is useful in cases of anatomical distortion to maintain orientation given the limited visualization.

Ipsilateral laminotomy of the level of interest is performed using a high-speed drill and the ligamentum flavum is left in place to protect the dura until bony removal is finished. The tube is then angled ~ 45° off the midline so that the tube is oriented to allow visualization and decompression of the contralateral side. The contralateral drilling can be tailored to the lesion; for example, if the lesion is located only ipsilateral, then complete contralateral decompression is not required, and exposure of at least the midline to allow space for enough durotomy and closure is recommended. To safely drill along the underside of the spinous process, a tissue plane can be developed between the ligamentum flavum and undersurface of the spinous process through dissection with a fine curet. Either using the suction to retract the ligamentum away from the drill or using an adjustable guard sleeve extended to cover the tip of the drill allows for safe drilling along the undersurface of the spinous process and contralateral lamina all the way to the contralateral facet. This initial decompression allows greater working space within which to remove hypertrophied ligament while avoiding downward pressure on the dura and spinal cord. Dissection and removal of the ligamentum flavum with curets and Kerrison rongeurs may now proceed safely. Any compressive elements of the contralateral facet or the superior edge of the caudal lamina may also be drilled off or removed with Kerrison rongeurs at this time, because their compression on the dura is most apparent once the ligament is removed. After confirming decompression of the contralateral foramen with a fine probe, the tube is returned to its original position to complete the ipsilateral removal of ligament and bone. This should then reveal completely decompressed and pulsatile dura. If indicated, ipsilateral foraminotomy, as described earlier, also may be performed at this time. Decompression and irrigation may be all that is required in cases of infection.

For intradural work, it is important to ensure enough bony decompression and dural exposure to allow for the durotomy and its closure. The operating room microscope is used for cases of tumor resection. An ultrasound with a long, small tip can be used to help guide the extent of decompression needed. The durotomy is carefully started with a long-handled scalpel, and a favored technique is to use straight hooks to open the dura longitudinally while preserving the arachnoid plane. Preserving the arachnoid is ideal to minimize early flooding of the exposure with CSF and epidural blood. The dural edges can be held open with tack-up sutures pulled up out of the tube retractor and held with hemostats (Fig. 51.2).

Fig. 51.2 Intraoperative views of sequential resection of intradural extramedullary tumor. For all views, rostral is to the reader’s left, caudal to the right, medial superior, and lateral inferior: (a) Tubular retractor in place with laminectomy performed and thecal sac visible through the retractor. (b) Microscope view through the tubular retractor with dural tack-up sutures in place exiting outside of the tubular retractor and durotomy performed, exposing the arachnoid. (c) Extramedullary lesion being delivered away from the spinal cord. (d) Intradural exposure after removal of the lesion.

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