Overview
The transthoracic approach to the midthoracic level is indicated when the anterior column is involved with tumor mass. This approach enables surgeons to accomplish complete ventral decompression of the spinal cord with simultaneous anterior reconstruction. Depending on the intactness of the pleura, two kinds of approaches might be taken: transpleural or extrapleural. Patients should possess competent lung function to perform one-lung ventilation. If preoperative evaluation shows a partial pressure of oxygen (P o 2 ) of less than 60, partial pressure of carbon dioxide (P co 2 ) of more than 45, oxygen (O 2 ) saturation below 90%, forced vital capacity (FVC) less than 1.5 L, forced expiratory volume in 1 second (FEV 1 ) less than 1 L, and FEV 1 /FVC less than 35%, the transthoracic approach is contraindicated.
Transthoracic Approach to the Midthoracic Level
Positioning and Incision
The operation is performed with the patient in a lateral decubitus position with an axillary roll under the dependent axilla ( Fig. 35-1 ). The patient’s body should be extended with the kidney rest and by the tilting of the operating table. The side of approach is decided based on the location of the pathology. When possible, a right-sided approach is preferred in the middle and upper thoracic spine, because more working space is available over the spinal surface behind the azygos vein compared with that behind the aorta. The left side is preferred for the lower thoracic spine, because at this level, the liver causes the right diaphragm to rise and partially obstruct the working space. The skin incision starts from four fingerbreadths lateral to the spinous process, runs along the selected rib, and reaches anteriorly to the costochondral junction.
Muscle Dissection
The latissimus dorsi muscle is then divided in a transverse direction relative to the fibers ( Fig. 35-2 ). In the anterior region of the opening, the anterior serratus muscle is exposed; posteriorly, the trapezius muscle can be exposed. When severing this muscle, the incision line should be as far caudal as possible to save the long thoracic nerve.
After the superficial muscle layer is divided, the second layer of muscles is exposed. According to the level of the lesion, rhomboids (superior), serratus anterior (anterior), and serratus posterior inferior (posterior) can be severed ( Fig. 35-3 ). In cases that involve the upper thoracic level, mobilization of the scapula is required.
Rib Removal
The selection of the rib to be removed is dependent on the lesion site. With lateral radiographs, the rib seen to be overlying the pathologic vertebral body can be determined. In general, an interspace of at least two levels above the level of the vertebral body involvement should be entered, and the rib below is resected.
The outer periosteum of the selected rib is incised sharply and stripped with a periosteal elevator ( Fig. 35-4 ). On preparing the outer and superior surfaces of the rib, a small dissector is used to free the inner periosteum from the underlying pleura. A Doyen elevator is introduced to elevate the inner periosteum anteriorly from the costal junction to the angle of the rib posteriorly ( Fig. 35-5 ). A rib cutter is used to remove the rib. To gain additional exposure of the rib posteriorly, a longitudinal incision is made along the anterior border of the paraspinal muscles to allow them to be retracted posteriorly past the rib angle.
Exposure of Vertebral Body (Transpleural)
The thoracic cavity is opened in the bed of the resected rib. The spine is exposed by a longitudinal incision of the pleura 5 mm anterior to the rib heads. The lung is retracted anteriorly, and the vertebral body is exposed with the parietal pleura covered. Underneath the parietal pleura, the rib head is seen to be in contact with the intervertebral disk. On palpation, the intervertebral disk spaces are prominent, and the segmental vessels generally cross the middle portion of the body.
A transverse incision of the parietal pleura is made along the rib head and disk space to expose the segmental vessels. In cases of a T8 body lesion, dissection starts from adjacent levels (T7 and T9). The parietal pleura overlying the segmental vessels are swept away with a monopolar coagulator ( Fig. 35-6 ).
The segmental vessels are coagulated and divided ( Fig. 35-7 ). The segmental vessels are dissected from the underlying vertebral body with a right-angle dissector, and hemoclips are applied to two sites, proximal and distal; the proximal side is controlled first, and later the distal side. After the hemoclips are applied to both sides, the vessel is cut and retracted. The sympathetic ganglion is removed to expose the rib head. For further exposure of the anterior portion of the vertebral body, the great vessels should be dissected. The space between the anterior longitudinal ligaments (ALLs) and great vessels is easily created by blunt dissection after the segmental vessels are disconnected. The removal of the rib head is mandatory for the exposure of the intervertebral foramen and posterior margin of the vertebral body. The rib head is drilled away, and the shell is removed with a curette. After rib head removal is complete, the costovertebral joint is exposed.
Vertebral Body Resection
After the parietal pleura is reflected and segmental vessels are controlled, the corpectomy begins. Adjacent disk removal is completed with an osteotome and pituitary forceps. The tumor-infiltrated vertebral body is slightly soft and friable. The resection boundary is confined with an osteotome, and an internal debulking is performed with pituitary forceps ( Fig. 35-8 ). For the exposure of the ventral surface of the spinal cord, the posterior cortical shell of the vertebral body should be removed. When the posterior cortex is removed, great care should be taken not to injure the spinal cord.
Exposure of the Vertebral Body (Extrapleural)
When a patient’s pulmonary function is not sustainable for one-lung ventilation, an extrapleural approach can be considered. Although this approach provides limited exposure compared with the transpleural approach, one advantage is that it can be done with lung retraction without lung collapse. After rib removal, the endothoracic fascia is incised; the parietal pleura is kept intact. The dissection is performed between the endothoracic fascia and the parietal pleura ( Fig. 35-9 ). This dissection provides the way to the vertebral body ( Fig. 35-10 ).
Bilateral Segmental Vessel Ligation
In a study involving dogs, the interruption of the bilateral segmental arteries at three levels, one targeting the vertebra and the other two the adjacent vertebrae, reduced the blood flow of the target vertebra to one fourth of the control value in the lower thoracic spine. This experimental result suggests that preoperative embolization at three levels, the levels of the tumor vertebra and the adjacent vertebrae above and below, may reduce intraoperative hemorrhage effectively during total en bloc spondylectomy for hypervascular spinal tumors. When the embolization fails, intraoperative ligation of the segmental vessels can lessen tumor bleeding. If the interruption of the bilateral segmental arteries is planned, the Adamkiewicz artery should be identified on preoperative angiography to be excluded from the ligation.
In the thoracic region, parietal pleural incisions are made on each vertebral body level and corresponding rib head. After the dissection of the parietal pleura, the segmental vessels are seen on the midpoint of the vertebral bodies. First, the segmental vessels on the approach side are ligated ( Fig. 35-11 ). Great care should be taken to dissect the vessel from the tumor-infiltrated cortical surface. After vessel ligation, the interface between the aorta and vertebral body anterior surface is dissected. With traction applied to the proximal portion of the ligated segmental vessels, the great vessels are moved to the anterior side to form a potential space relative to the ALL ( Fig. 35-12 ).
An adhesion may exist between the tumor-infiltrated vertebral body and great vessels. However, the dissection is relatively easy, because the ALL blocks ventral expansion of the tumor mass. When the great vessels are moved forward, the segmental vessels on the contralateral side are seen to wind around the lateral surface of the vertebral bodies. The exposed field is very deep. A surgical instrument such as the right-angle dissector is applied to the contralateral segmental vessels, which are cut and tied ( Figs. 35-13 and 35-14 ). Great care should be taken not to stretch these vessels. Neurologic deficit after unilateral left-sided ligation of the T10–T12 segmental vessels occurs in 0.75% of patients. The risk of segmental vessel ligation is minuscule provided 1) vessel ligation is unilateral, 2) ligation is done on the convexity of a scoliosis, 3) vessels are ligated at the midvertebral body level, and 4) hypotensive anesthesia is avoided.
Anterior Approach to Thoracolumbar Junction (Transpleural-Transdiaphragmatic Approach with Tenth Rib Resection)
The exposure of the thoracolumbar junction (TLJ) can be approached through either side, but a left-sided approach is often selected, for which the patient is placed in the true lateral decubitus position with a beanbag under the flank. For the exposure of T11–T12, the resection of the ninth rib is usually best, and at T12–L1, a tenth rib thoracoabdominal approach is preferred. In this approach, long exposure of the thoracic and lumbar spines is possible from the T10 vertebral body down to L3 level. This approach involves detaching the diaphragm at its circumference.
When the diaphragm should not be taken down, or when less exposure is needed, the twelfth rib approach is used. For L1–L2 exposure, a twelfth rib extrapleural retroperitoneal approach is recommended. The eleventh rib exposure is the highest practical, extrapleural, retroperitoneal approach for exposure of T10–L2. It avoids opening the pleural cavity and cutting the diaphragm in patients with the potential for high morbidity.
Positioning and Incision
The patient is placed in the lateral decubitus position. The skin incision begins posteriorly near the midline, follows the course of the tenth rib as far as the costal cartilage, and then continues obliquely downward on the upper abdomen, following the direction of the segmental nerves ( Fig. 35-15 ). The procedures are performed to expose the thoracic cavity first, followed by the exposure of the abdomen, and then the two parts are joined.
Soft Tissue Dissection
Using cautery, the incision is deepened down through the thoracic muscles, and the latissimus dorsi muscle and serratus anterior muscles are transected posteriorly ( Fig. 35-16 ). The deep abdominal muscle layers (internal oblique and transverse muscles of the abdomen) are bluntly split and retracted to allow exposure of the upper lumbar spine retroperitonially.
Rib Removal
The superficial periosteum is stripped out with cautery from the rib to the costal cartilage, and the ribs are dissected subperiosteally with a periosteal elevator and Doyen elevator. The neurovascular bundle that lies below the rib is carefully isolated and ligated.
The rib is removed using a rib cutter from the angle of the rib posteriorly to the costal cartilage anteriorly ( Fig. 35-17 ). The pleural cavity extends over the majority of the eleventh rib and the medial portion of the twelfth rib. The endothoracic fascia and the pleura are carefully stripped from the inner surface of the rib.
The thorax is opened with the incision of the periosteal layer of the removed rib bed and the parietal pleura. Using a sponge stick, the diaphragm is kept under tension and is gradually detached from its costal insertion and posteriorly from the eleventh and twelfth ribs.
Diaphragm Incision
For exposure of the T12–L1 vertebral body, diaphragmatic detachment is required. Anatomically, the diaphragmatic muscle fibers originate from three locations: the sternal, costal, and lumbar parts. The lumbar part arises from both the right and left crura and from the medial and lateral arcuate ligaments, the sternal part originates from two muscular slips from the dorsum of the xiphoid process, and the costal part arises from the inner surfaces of the costal cartilages and adjacent portions of the bone of the last six ribs on either side. The right crus begins from the sides of the L1–L3 bodies, and the left crus begins from the sides of the L1 and L2 bodies. The medial arcuate ligament covers the upper part of the psoas major muscle, attaching from the sides of the first and second lumbar vertebrae to the tip of the L1 and L2 transverse processes. The lateral arcuate ligament covers the quadratus lumborum and attaches from the tip of the L1 transverse process and laterally to the lower border of the twelfth rib. Thus both the crura and arcuate ligaments of the diaphragm are inserted below the T12–L1 disk space, so lesions located above the T12–L1 disk can be approached from above without dividing the diaphragm. Below the T12–L1 disk space, the spine is surrounded by the diaphragmatic crura, psoas muscles, and arcuate ligaments, so injuries here require diaphragmatic detachment for adequate exposure.
The diaphragmatic incision is made from inside the chest with clear visualization under the diaphragm in the retroperitoneal space ( Fig. 35-18 ). The incision may be extended circumferentially 1 inch from its peripheral attachment to the chest wall. For an accurate reapproximation, marker clips should be used throughout the takedown of the diaphragm ( Fig. 35-19 ).
Exposure of Each Vertebral Body
After the longitudinal incision of the parietal pleura, the dissection is done over the intervertebral disk space, until the base of the transverse processes is reached. The sympathetic trunk is retracted laterally ( Fig. 35-20 ). The origins of the psoas muscles are stripped from the vertebral body. The intercostal arteries and veins are tied and ligated to allow mobilization of the major vascular trunk ( Fig. 35-21 ). The twelfth intercostal vessels and first lumbar artery and vein may be covered by the muscular crus of the diaphragm.
For the cephalad extension of the operative field, the parietal pleura can be incised to the lower thoracic spine. In the lower thoracic spine, the aorta is located slightly to the left of the vertebral body compared with the L1 body level. For the exposure of the vertebral body at the lower thoracic level, the aorta should be mobilized to the midline.
Closure
The diaphragm is reattached starting with approximation of the divided crus using a polydioxanone (PDS) No. 0 monofilament and proceeding as a continuous or interrupted suture along the periphery of the divided diaphragm to the site of the division of the costal arch ( Fig. 35-22 ). If the instrument is left on the vertebral body, the crus connection may be incomplete. The diaphragm repair is done over the implant applied to the vertebral body ( Fig. 35-23 ). The divided costal cartilage serves as a good landmark for closure and should be reapproximated with two No. 0 or 1 braided polyester sutures used as a figure-eight. Closure of the diaphragm is completed by additional stitches.
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