Transthoracic Thoracic Diskectomy

Thoracic disk herniation (TDH) is a common spinal disorder, with an estimated radiographic prevalence of 11% to 37%. ¹^, ²^, ³ Clinically symptomatic TDH is rare, however, occurring in as few as one per one million patients. ⁴ When operative intervention is indicated, safe and effective execution of the appropriately selected technique is critical for achieving favorable outcomes. Herein, we discuss the surgical indications, operative nuances, and postoperative management for the transthoracic anterolateral approaches, thoracotomy, and thoracoscopy.

31.2 Patient Selection

Because most cases of TDH are asymptomatic, nonoperative management is appropriate for most patients. Surgical decompression should, however, be considered for two primary scenarios: (1) radiographic evidence of spinal cord compression with signs or symptoms of myelopathy; and 2) radiographic evidence of nerve root compression with severe, protracted radicular pain that has not responded to nonoperative management. Surgical decompression is most commonly achieved via either a transthoracic anterolateral or an extracavitary posterolateral approach. Although the posterolateral approach is effective for small, soft, laterally oriented disk herniations, the transthoracic anterolateral corridor is preferred for TDHs that are large, calcified, or centrally located.

Transthoracic approaches include both traditional open thoracotomy and thoracoscopy, and each has distinct advantages and disadvantages. As a minimally invasive alternative to open thoracotomy, thoracoscopy offers a reduction in approach-related morbidity, ⁵^, ⁶^, ⁷^, ⁸ but it is technically challenging and requires significant experience to be conducted proficiently. In contrast, the open thoracotomy offers superior bimanual dexterity and thus remains the preferred approach for severe pathology; however, open thoracotomy is associated with increased blood loss, higher transfusion rates, longer chest tube duration, higher rates of intercostal neuralgia, and longer hospital stays. ⁶^, ⁷ Thus, its consideration should take into account the specifics of the pathology and general health of the patient. Likewise, when thoracoscopy is being considered, careful attention must be paid to any history of thoracic surgery, rib fractures, or pneumonia because preexisting pleural adhesions can prevent adequate visualization of the pleural cavity. Both thoracoscopy and thoracotomy require single-lung ventilation, and transthoracic approaches are contraindicated when single-lung ventilation cannot be performed. Patients should be informed of the possibility that a thoracoscopic procedure may have to be converted to an open thoracotomy. In general, thoracoscopy is preferred for soft, midline TDH, and open thoracotomy is preferred for large or calcified TDH. ⁵

31.3 Preoperative Preparation

Transthoracic approaches for the treatment of TDH require meticulous preoperative planning. Imaging studies (e.g., plain radiographs and magnetic resonance imaging [MRI] scans) should be obtained and carefully studied. Fine-cut computed tomography (CT) may be helpful in identifying the presence or absence of disk calcification. Localization of the appropriate level requires detailed analysis of all preoperative and intraoperative imaging. All preoperative localization images on MRI and CT should be studied by the surgeon, and ribs should be counted using anteroposterior radiographs. Use of intraoperative fluoroscopy is critical for determining the appropriate level. An alternative strategy for level localization involves the preoperative placement of a radiopaque fiducial at the adjacent vertebral pedicle. The fiducial can then be easily identified intraoperatively with fluoroscopy.

Multimodal intraoperative neuromonitoring has become the standard of care during complex spine surgery at many institutions, and it should be used during transthoracic thoracic diskectomy when available; this is especially important for higher risk lesions (e.g., giant calcified TDH). Given the importance of single-lung ventilation, patients must have adequate cardiopulmonary function so that selective bronchial intubation can be tolerated for a prolonged period. For maintenance of optimal hemodynamics, cell saver and blood products should be made available, especially for patients requiring multilevel diskectomies and for patients who are frail or anemic. Preoperatively, the side of approach must also be determined. Normal thoracic anatomy plays a key role in guiding the side selection. For most upper thoracic lesions, a right-sided approach is preferable because it makes available more working space over the spinal surface behind the azygos vein compared with the area behind the aorta. The midthoracic levels can be exposed from either side, with the side of the approach determined by the location of the pathology and the position of the aorta, azygos vein, and other structures. Lower thoracic levels are most easily accessed from the left side because caudal exposure is not impeded by the liver. These considerations are merely guidelines, however; the regional thoracic anatomy of each patient and the details of the patient’s pathology must be thoroughly evaluated so that the optimal approach can be determined.

31.4 Operative Procedure

The patient is intubated with a double-lumen endotracheal tube, and intravascular access is obtained. Next, baseline somatosensory and motor evoked potentials are recorded. The patient is positioned in the lateral decubitus position with the operative side up and the ventilated lung in the dependent position ( ▶ Fig. 31.1 a). The lower leg is flexed, an axillary roll is placed, and all pressure points are adequately padded. After positioning, the stability of the somatosensory and motor evoked potentials is confirmed. C-arm fluoroscopic imaging is used to localize the correct level for surgery, as discussed already herein. Before the incision is made, the ipsilateral lung is deflated. Intermittent reinflation in 30- to 60-minute intervals during the case may help protect against postoperative atelectasis.

Fig. 31.1 (a) Patient positioned for left thoracotomy. The position of the scapula and a midthoracic thoracotomy incision are marked on the chest wall. (b) Portal positioning for a left thoracoscopic approach to the midthoracic spine for diskectomy. The portals are placed along the anterior, middle, and posterior axillary lines around the level of the disk herniation, with adequate separation between portals to optimize surgical freedom. The endoscope is placed through the posterior portal, and a retractor is placed through the anterior portal. The middle axillary portals are used for other instruments. (c) During thoracoscopic procedures, the surgeon stands in front of the patient at the level of the approach. Video monitors are positioned to allow the surgeon and the surgical assistant to comfortably view the footage from the endoscope. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.)

31.4.1 Thoracotomy

The skin incision for an open thoracotomy is made parallel to the ribs at one or two levels above the pathology. The incision is marked, the surgical site is washed with either iodine or Chlor-hexidine, and drapes are placed. Skin is infiltrated with 0.5% bupivacaine, and an intercostal block is performed. After the incision is made, subperiosteal dissection is performed to strip away the intercostal muscles and neurovascular bundle. The rib is subsequently resected and the pleura incised. A rib spreader is then inserted, and sponges are packed into the thoracic cavity to keep the deflated lung clear of the operative site. Adequate visualization of T11 to L1 requires division of the diaphragm 1 cm from the costal margin to access the retroperitoneal space.

31.4.2 Thoracoscopy

Proper portal arrangement is essential to ensure adequate visualization of the levels of interest. In a routine single-level diskectomy, three to four portals are placed around the affected level ( ▶ Fig. 31.1 b). The first portal is positioned at the posterior axillary line. Others are positioned near the middle and anterior axillary lines at separate intercostal spaces. These portals are spaced across the surface of the chest to improve operative dexterity and maximize the freedom of the surgical instruments. The incisions are marked, the surgical site is washed with either iodine or chlorhexidine, and drapes are placed. The skin is infiltrated with 0.5% bupivacaine, and an intercostal block is performed. The surgeon stands in front of the patient at the level of the approach, and the assistant stands cross-table. Video monitors are positioned to allow the surgeon and the surgical assistant to comfortably view the video feed from the endoscope ( ▶ Fig. 31.2 c).

Fig. 31.2 Thoracoscopic surgical instrumentation. Top to bottom: Suction and irrigation, right-angled clamp, endoshears, fine tissue forceps, ringed tissue forceps, Babcock clamp, long drill bits and cutting burs, shafts for the drill attachment, osteotomes, periosteal elevator, bone graft impactor, curette, straight osteotome, peanut dissectors, and endoscopic Avitene delivery tube. Left: Flexible and rigid thoracoscopic portals. Right: Right-angled hemoclip applier, bipolar cautery forceps, and fan retractor. (Reproduced with permission from Dickman et al. ⁸)

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