Endoscopic Approaches to Thoracic Tumors, Trauma, and Infection

36 Endoscopic Approaches to Thoracic Tumors, Trauma, and Infection

Christopher C. Gillis and John O’Toole

36.1 Introduction

A variety of surgical approaches have been proposed and implemented in the treatment of thoracic spine pathology, with the latest advancements geared toward minimally invasive options.1,2,3,4,5,6 The direct open posterior approach can be used in cases of purely dorsal disease but otherwise is unfavorable in the thoracic region due to the requirement for retraction of the thoracic cord instead of cauda equina nerve roots.4,5,6,7 The thoracic cord is especially sensitive to minimal retraction, and this has been postulated to be the cause of the relatively poor outcomes that had traditionally been seen with posterior approaches to more central and ventral pathology.1,4 This has led surgeons away from direct posterior approaches to posterolateral approaches, including both costotransversectomy and transpedicular trajectories, which used more extensive bone removal to minimize manipulation of neurologic structures and have thus been shown to be much safer than a direct posterior approach. These posterolateral approaches, however, result in removal of supportive bone structures that often necessitates fusion for prevention of postoperative instability and can also lead to increased postoperative pain and morbidity. Open anterior and lateral approaches have also been used, and are associated with complications related to the approach through the thoracic cavity, such as risk of injury to vital thoracic structures and vessels, pulmonary contusion, hemothorax, chylothorax, intraoperative and postoperative difficulty with ventilation, shoulder girdle dysfunction, and difficulty with wound healing.4

36.2 Minimally Invasive Approaches

Minimally invasive options include endoscopic lateral retropleural decompression, minimally invasive transpedicular decompression, and thoracic microendoscopic decompression (TMED).4 TMED is a modification of the lumbar microendoscopic technique. Benefits of this approach include sparing of the majority pedicle, which must be removed in the transpedicular approach, and the avoidance of rib resection, required in the lateral retropleural approach.4,5,6 Use of the endoscope is not required for visualization during this approach, and a similar approach using tubular muscle retractors can be used for a variety of thoracic pathologies, with the use of loupe, microscope, or endoscopic visualization.5,6 Once a laminectomy is performed through either a direct posterior approach or a more lateral transpedicular approach, depending on the angle of pathology presenting, both ventral and dorsal decompression can be achieved, as well as durotomy and resection of intradural lesions. Tredway et al8 successfully adapted a minimally invasive unilateral laminotomy approach for resection of intradural extramedullary lesions in both the cervical and thoracic spine. The lateral retropleural approach allows easier access for vertebral body decompression and can be performed in a fashion very similar to lateral lumbar interbody fusion (LLIF), using the same retractor system with long retraction blades. For cases of trauma or instability related to tumor or approach, instrumentation can be achieved through the use of percutaneous screw placement with fluoroscopic or navigation guidance.

36.3 Choice of Patient

36.3.1 Indications

The choice of minimally invasive approach depends on the area to be decompressed, the presence or absence of instability, and the primary location of the pathology. As an example, ventral decompression can be achieved through both the transpedicular and direct lateral retropleural approach, with the lateral retropleural ideal for more central ventral pathology than can be reached through a transpedicular approach. Direct dorsal decompression or paramedian dorsal decompression can be achieved through a more direct posterior approach. Once decompression is achieved, for tumor, trauma, or infection, the next step is determination of the presence of instability, which would require supplemental instrumentation with percutaneous pedicle screw and rod placement.

In the direct lateral approach, as in LLIF, vertebrectomy and cage placement can be used in cases of severe burst fracture or significant bony infiltration of tumor.9,10 In cases of metastases, however, the need for complete tumor resection has been minimized through the concept of separation surgery,11,12 which requires decompression of the neural elements with adjuvant (often stereotactic) radiotherapy for treatment. A minimally invasive corpectomy can also be performed through a posterolateral approach by taking a more lateral trajectory (average of 6 cm off midline) and approaching through a corridor similar to that used for an open costotransversectomy.

36.3.2 Contraindications

As in most minimally invasive procedures, the approach is limited by the retractor size and thus is left mostly to lesions spanning one to two spinal levels. Some surgeons have successfully performed staggered contralateral skip laminectomies for larger lesions. Primary bony tumors requiring complete vertebrectomy in the thoracic area are likely best approached through a combination of anterior and posterior approaches, which may involve a combination of minimally invasive and open techniques.13

36.4 Procedure

36.4.1 Level Identification

One of the most important steps, irrespective of the technique used, is appropriate identification of the surgical level. Identification of the surgical level in the thoracic spine is more difficult than in the cervical or lumbar spine, where counting of levels facilitates knowledge of the appropriate level. This is due to the distance of the thoracic spine from the skull or sacrum, individual variance in regional anatomy and the number of ribs that can be used for counting, and poor fluoroscopic penetration in upper thoracic levels—especially in patients with increased subcutaneous fat. We have found that careful preoperative examination of ribs and levels combined with careful fluoroscopic intraoperative counting has allowed identification of the appropriate level. Other described adjuncts for level identification include percutaneous placement of radiographic skin markers, percutaneous placement of a radiopaque marker at the periosteum of the pedicle of interest, percutaneous injection of methylene blue dye, and even preoperative vertebroplasty; however, none of these adjuncts has gained widespread use.14 Depending on the procedure being performed, intraoperative neuronavigation can help with the identification of level, but it requires an intraoperative CT scan and is not usually of benefit in cases without instrumentation placement. At our center, we rely on anatomical landmarks and level counting with both lateral and anteroposterior fluoroscopic views.

36.4.2 Decompression

The lateral transpedicular or direct dorsal decompressive procedure is done with the patient in the prone position and under general anesthetic, in a fashion similar to minimally invasive laminectomy elsewhere in the spine. A radiolucent Jackson table with appropriate chest and hip pads facilitates use of fluoroscopy during the case. Arms can be tucked with sheets for upper thoracic cases, and positioned on arm boards for lower thoracic cases, with care to appropriately pad the elbows, and especially the ulnar nerve, as well avoiding extension of the arms greater than 90°. It is the practice of many surgeons to obtain continuous somatosensory evoked potentials throughout the procedure. Some advocate for motor evoked potentials (MEP) as well.

Once the appropriate level has been identified and marked as described above, an incision is made between 3 and 4 cm lateral to the midline. In cases where thoracic corpectomy is to be performed, an even more lateral trajectory is desired, which averages 6 cm from midline. In obese patients or patients with an increased amount of subcutaneous tissue, it is useful to take a more lateral trajectory. The goal of entering laterally is to minimize manipulation of the thecal sac and spinal cord during the procedure. Through the incision, a K-wire is inserted at the rostral side of the caudal transverse process of the level of interest. Serial tubular muscle dilators are then placed over the K-wire under fluoroscopic guidance. Care is taken to ensure the K-wire remains on bone throughout the dilation, to prevent migration. After dilation is complete, the tubular retractor is placed over the dilators and fixed to the rigid retractor arm, attached to the operating table. Through the tubular retractor, a microscope, loupes, and a headlight or an endoscope with a 30° lens can be used for visualization. When using the endoscope, it is useful to orient the scope so that medial is located at the top of the monitor and lateral at the bottom, bringing the rostral-caudal axis along the horizontal.

Remnant muscle and soft tissue at the bottom of the tubular retractor is then dissected away using monopolar cautery and can be removed from the field with a pituitary rongeur. With this small amount of soft tissue removal, the proximal transverse process and the lateral facet are exposed. The tubular retractor can be adjusted to bring the facet–transverse process junction into the middle of the field of view for optimal working exposure. The high-speed drill is then used to remove the rostral aspect of the inferior transverse process and the lateral facet until the pedicle of the caudal vertebral body is exposed. The pedicle is then followed ventrally to identify the disk space; drilling a portion of the rostral aspect of this pedicle allows a better working corridor into the disk space if this is required, such as in a case of diskitis. Due to the lateral trajectory, minimal to no manipulation of the thecal sac is required. Laterally placed tumor, bone fragment, or abscess is readily identified and more medial pathology can be dissected away from the thecal sac, underneath the annulus, with downpushing curets into the disk space or resection cavity, where they are then safely retrieved.

In thoracic corpectomy through the posterior approach, greater bony removal involves resection of a longer segment of the rib from medial to lateral. This provides a greater space for expansion and angling of a retractor for visualization. From a unilateral approach, the disk above, the vertebral body, and the disk below can all be resected through a combination of curets and drilling. After bone removal, an expandable intervertebral cage can be placed, supported by the remaining cortical bone from the contralateral side. If contralateral decompression is desired, a bilateral approach can be used. An illustration of the approach angle and bone removal is seen in Fig. 36.1a, and postoperative CT from a thoracic minimally invasive corpectomy is seen in Fig. 36.1b.

After decompression, the field is irrigated and meticulous hemostasis is achieved, especially in the muscle edges, which are carefully inspected as the tubular retractor is removed. Absorbable Vicryl sutures are used in the fascia and then in the subcutaneous tissue. For the skin, skin glue, a continuous subcuticular monofilament suture, or skin tape can be used to augment the subcutaneous stitch.

Mar 29, 2020 | Posted by in ORTHOPEDIC | Comments Off on Endoscopic Approaches to Thoracic Tumors, Trauma, and Infection
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