Minimally invasive thoracic surgery

Imagine exploring the thoracic cavity and performing surgical interventions without using an intercostal or a median sternotomy. This is possible when you perform thoracoscopy—a technique widely used in human thoracic and cardiac surgery. Minimally invasive video-assisted endoscopy and minimally invasive surgical instrumentation allow practitioners to perform diagnostic and advanced therapeutic procedures in the thoracic cavity.1 Thoracoscopy is indicated for exploration of the thoracic cavity, diagnosis of pleural effusion of unknown origin, and pericardial effusion.2-4 Biopsy of the pleural surface, lymph nodes, pericardium, and lungs can be performed during thoracic cavity exploration. Veterinary literature reports the use of thoracoscopy to perform lung lobectomies, ligate thoracic ducts, and correct persistent right aortic arches.5-8

Eric Monnet, DVM, MD, PhD, DACVS, DECVS

What you will need

The basic thoracoscopy equipment includes a surgical telescope (

Figure 1

), trocar-cannulas, a basic set of thoracoscopic surgical instruments, a light source, a video camera, and a video monitor (

Table 1

). Thoracoscopy doesn't require CO2 insufflation because the rib cage keeps the thoracic cavity expanded.

Telescopes

Telescopes used for thoracoscopy are most commonly 5 mm in diameter and 30 cm long. This scope size works in a wide range of animals. Telescopes are available with different angles, and the forward-view 0-degree and the forward oblique 30-degree telescopes are most commonly used. The 0-degree telescope allows a natural field of view and a normal perspective to organ orientation. The 30- degree telescopes allow better visualization of areas in the thoracic cavity that are difficult to access. However, orientation and manipulation are more difficult with the angled scopes.

Cannulas

Cannulas for thoracoscopy are either open or closed. Closed cannulas feature a valve that allows the veterinarian to create a controlled pneumothorax. They can potentially induce a tension pneumothorax during the procedure. Open cannulas create an open chest, as in a thoracotomy. Open cannulas are preferred for long surgical procedures because they reduce the risk for tension pneumothorax. Cannulas come in different diameters. The recommended diameter is 12 mm because most stapling equipment available for thoracoscopy is 10 mm in diameter.

Instruments

Numerous instruments are available for endoscopic exploration and surgery. The basic instrument set consists of grasping forceps, scissors, biopsy forceps, and a palpation probe. Forceps and scissors are insulated for electrocautery. Electrocautery can be used to cauterize small blood vessels during resection of the mediastinum or pericardium. For lung biopsies, pretied ligatures can be used, which eliminate the need for knot tying inside the thoracic cavity. Retractors are required to hold lungs away from the camera and obtain a clearer surgical field. Ligating small blood vessels in the mediastinum requires vascular clip applicators, which come in different sizes, and lung lobe resections necessitate the use of stapling equipment. The Endo GIA stapling device (Tyco Healthcare/Kendall Animal Health) comes in three lengths: 30, 45, and 60 mm. Staples come in lengths of 2.0, 2.5, 3.5, or 4.8 mm. Finally, suction and irrigation devices are available to aspirate blood during the procedure and lavage the surgical field and thoracic cavity.

Figure1. A 5-mm forward view telescope. The telescope is 30 cm long.

As for equipment, two types are recommended for advanced surgical procedures using minimally invasive surgery: radiofrequency and ultrasound-based equipment. They provide fast, safe sealing of blood vessels without using suture materials. Radiofrequency equipment can safely seal an artery with a diameter of less than 7 mm. Ultrasound-based equipment allows the practitioner to cut through the tissue and seal the blood vessels. Vessels sealed using ultrasound technology should have a diameter of less than 3 mm.

Approaches

Thoracoscopy can be performed using a transdiaphragmatic or an intercostal approach. The transdiaphragmatic approach is preferred for exploration of the thoracic cavity and biopsy because it allows visualization of both hemithoraces. A long axis view of the thorax is then obtained. The intercostal approach allows visualization of only one side of the thoracic cavity, but it gives a better visualization of the dorsal part of the thoracic cavity. A thorough exploration of the thoracic cavity (with either approach) requires at least three cannulas.

Table 1. Thoracoscopy instruments and sources

Transdiaphragmatic approach

With the patient positioned in dorsal recumbency, a small skin incision is made caudal to the xiphoid. A screw-in cannula is then inserted in a subxiphoid position in a cranial direction. The cannula is screwed in the thoracic cavity under thoracoscopic visualization. After the cannula penetrates the thoracic cavity, the thoracoscope is advanced in the thoracic cavity. At the beginning of the exploration, a 0-degree telescope is used. At this time, only one hemithorax can be visualized because the mediastinum is intact.

After exploring the thoracic cavity, two additional cannulas are placed to allow instrument use. To allow maximum instrument mobility, these cannulas are most commonly placed in the eighth intercostal space in the left and right side of the thoracic cavity as ventrally as possible. To place the cannulas, the skin is incised with a No. 10 blade. The incision length should match the cannula's diameter. Next, forceps are used to bluntly dissect the thoracic wall and penetrate the thoracic cavity. The cannula is introduced over a blunt obturator under thoracoscopic visualization.

Figure 2. The pericardium is pulled toward the sternum. Scissors will be used to open the pericardium toward the apex.

With all portals in place, the ventral mediastinum of the sternum is cut to move it out of the visual and manipulative field. Scissors are used to cut the mediastinum, accompanied by electrosurgical assistance to control bleeding. Inadequate control of bleeding from the mediastinal vessels interferes with the procedure by allowing blood to drip onto the telescope and obscure visualization. Dissection of the mediastinum will allow exploration of both hemithoraces.

Intercostal approach

One-lung ventilation is used more often with the intercostal approach than the transdiaphragmatic approach. After placing the patient in lateral recumbency, cannulae are placed in the 10th, seventh, and eighth intercostal spaces. The thoracoscope is introduced in the thoracic cavity through the cannula in the 10th intercostal space. Instruments can then be introduced in the two other cannulae. The three cannulas are placed in a triangle fashion. Cannulas are placed as described for the transdiaphragmatic approach.

Figure 3. The pericardium is opened and a right atrial tumor is visible.

Surgical Procedures

Pericardial window

Creating a pericardial window establishes permanent drainage for patients with pericardial effusion. This minimally invasive approach greatly reduces operative trauma and postoperative pain.3,4 Indications for permanent pericardial drainage include neoplastic effusions, hemorrhage from neoplastic masses, inflammatory disease, and idiopathic effusions. This procedure prevents a cardiac tamponade from developing by allowing pericardial fluid to drain into the pleural space. Results with this procedure are excellent: long-term resolution for patients with idiopathic or inflammatory disease and dramatically improved quality of remaining life for patients with neoplasia.

The surgeon can use either a transdiaphragmatic or an intercostal approach to create a pericardial window in dogs. The intercostal approach on the right side allows better visualization of the right atrial appendage and aortic root. During the transdiaphragmatic approach, portals are placed in the left and right ninth to 10th intercostal spaces. All portals are placed ventral to the costochondral junction in the area of the lateral margin of the transverse thoracic muscles. For the intercostal approach, the camera portal is placed in the ventral third of the sixth or seventh intercostal space, and one instrument portal is placed in the fourth intercostal space, and another in the eighth intercostal space. This creates a pericardial window on the right side of the pericardium. Before incising the pericardium, however, the phrenic nerve must be identified.

Figure 4. Lung neoplasia in the middle of a caudal lung lobe. The diameter of the mass was 2 in, and it was located away from the hilus.

When creating a pericardial window, it's necessary to start toward the apex of the heart to avoid iatrogenic damage to the right atrial appendage. Babcock forceps or grasping forceps with teeth are used to pick up a fold of pericardium, and Metzenbaum scissors are used to cut into this elevated fold of tissue for initial penetration of the pericardium (Figure 2). Next, the graspers are repositioned to pick up a margin of the initial pericardial incision, and the window is then extended toward the base of the heart to expose the right atrium (Figure 3). Any excess pericardial fluid that hasn't been evacuated and interferes with visualization is removed with suction. The portion of pericardium removed needs to be large enough to prevent closure of the defect by the healing process and small enough to prevent the heart from herniating through the window. A 1-in to 2-in square patch is an acceptable size. The removed patch is extracted from the chest through one of the operative portals and inspected for size and to define pathology. Samples are submitted for histopathology and, if indicated, for cultures. Biopsy of the mediastinal lymph node is recommended because it may reveal pericardial mesothelioma that might not be apparent with the pericardial window sample.

Finally, the surgeon removes any residual pericardial and pleural fluid with suction and irrigates the cavities with saline. The operative portal cannulas are removed and the portals are closed in layers to achieve an airtight closure. Cruciate sutures are placed in the deep muscle layer, the subcutaneous tissue, and the skin. A thoracostomy drain is placed in a routine fashion through the chest wall. Its placement can be monitored with the thoracoscope.

Figure 5. Application of an Endo GIA stapling device at the hilus of the left caudal lung lobe.

Partial lung lobectomy

Lung biopsies for chronic lung disease and excision of lung masses, lung abscesses, emphysematous bullae, or any other localized disease process in the peripheral portions of the lung lobes can be performed effectively with a minimally invasive technique.9,10 A partial lung lobectomy can also be performed for diagnostic biopsy of generalized lung disease. In a partial lung lobectomy, the location of the lung tissue to be removed dictates portal placement. Dorsal recumbency and the transdiaphragmatic telescope portal allow examination of both sides of the chest when the side of the pathology can't be determined, such as with spontaneous pneumothorax. If the side of involvement can be determined preoperatively with radiographs or other diagnostic techniques, lateral recumbency is preferred because it provides greater unilateral access. To access the involved pathology, the telescope and operative portals are inserted using appropriate triangulation. For small peripheral lesions and for lung biopsies, a loop ligature technique can be used. The tip of the lobe to be removed is positioned through a pretied loop ligature, which is tightened, and the ligated portion of the lung is transected and removed. This technique is quick, easy, and saves the substantial expense of an endoscopic stapler. Larger or more central lesions require an endoscopic stapling device for occlusion and transection of the portion of the lobe to be removed. When performing partial lung lobectomy with an endoscopic stapler, the telescope and operative portals are placed, the lung lobe lesion is retracted or elevated as needed, and the endoscopic stapler is placed through an additional portal to provide optimal alignment for stapling. Following transection of the lung lobe, one of the portals is enlarged to allow the excised tissue to be removed. An endoscopic tissue pouch (

i.e.

, a sterile plastic bag used to retrieve a specimen from the thoracic cavity without contaminating the edges of the portals) is recommended to facilitate tissue removal. The transected lung margin should be observed for air leakage or bleeding before exiting the chest with the telescope. A chest drain is placed at a site away from all portals, operative and telescope cannulas are removed, and the portals are closed.

Figure 6. Biopsy of an enlarged hilar lymph node.

Lung lobectomy

A complete lung lobectomy can also be performed with a minimally invasive technique to treat lung cancer.8,11 Lung lobes with small masses that are away from the hilus of the lung can be removed with minimally invasive surgery (

Figure 4

). Large masses impair visualization of the hilus and make lung manipulation difficult. Lateral recumbency with intercostal portal placement is the preferred technique for a complete lung lobectomy. One-lung ventilation is recommended to increase the amount of space available in the thoracic cavity, which allows manipulation of the instruments and the lung mass. To begin the procedure, place a telescope portal and two operative portals using triangulation. The hilus of the lung lobe to be removed is exposed. For caudal lung lobes, divide the pulmonary ligament to free the lung lobe so it can be positioned for stapling with the endoscopic stapling device. The pulmonary artery and vein and the bronchi are not separated (

Figure 5

). A 45-mm to 65-mm long stapling cartridge with 3.5 mm staples is placed across the hilus of the lobe. The stapling cartridge must be long enough to include the entire hilus to be stapled. The resected lung lobe is removed from the chest through a small intercostal thoracotomy. Enlarged hilar lymph nodes can be biopsied with the minimally invasive technique (

Figure 6

). An endoscopic tissue pouch facilitates lung lobe removal and decreases the potential for seeding the chest wall with neoplastic cells or infection. Observe the hilus for air leakage or bleeding. Finally, a chest drain is placed at a site away from all portals. Cannulae are removed and the portals are sutured. Cruciate sutures are placed in the deep muscle layer, the subcutaneous tissue, and the skin.

Figure 7. A persistent right aortic arch has been dissected away from the esophagus.

Thoracic duct occlusion

Thoracic duct occlusion to manage chylothorax is possible with a minimally invasive technique.5 The telescope and video system magnify the site, enhancing visualization of the thoracic ducts, and instruments designed for minimally invasive surgery allow manipulation of structures deep in the chest. The thoracic duct can be occluded with vascular clips specifically designed for minimally invasive surgery or with radiofrequency equipment.

Intercostal portals are placed on the right lateral chest wall with the patient in ventral recumbency.The telescope portal is placed in the seventh intercostal space at the dorsoventral midpoint of the intercostal space. Operative portals are placed midway between the telescope portal and the dorsal end of the ribs in the sixth and ninth intercostal spaces. For clip application, the pleura is dissected to expose the thoracic ducts and multiple clips are applied to all visible duct branches. Injecting methylene blue into the popliteal lymph node or the cisterna chyli has been recommended to improve visualization of the thoracic duct.5

Figure 8. Vascular clips have been applied to the persistent right aortic arch, which has been cut between the two clips.

Persistent right aortic arch correction

In cases of persistent right aortic arch, minimally invasive transection of the ligamentum arteriosum is an effective alternative to the open surgical approach.6,7

To perform this minimally invasive surgery, the patient is placed in right lateral recumbency. The telescope portal is placed in the left fourth or fifth intercostal space at the costochondral junction, and operative portals are placed in the third and sixth or seventh intercostal spaces at the level of the costochondral junction and at the dorsal end of the fifth intercostal space. A retractor is placed in the sixth or seventh intercostal portal to retract the cranial lung lobe caudally. Placement of a stomach tube in the esophagus improves visualization of the esophagus and the ligamentum arteriosum during the surgery. A palpation probe is used to further localize the ligamentum arteriosum. The ligamentum arteriosum is isolated from the pleura and esophagus using sharp and blunt dissection (Figure 7). Endoscopic 5-mm vascular clips are placed on the isolated ligamentum arteriosum, which is transected between the clips (Figure 8). Any remaining fibers are dissected away from the esophagus and divided, and the esophagus is dilated by passing a balloon dilation catheter. The surgeon then places a chest tube and closes the portals. Postoperative dietary management is the same as in the open surgical approach.

Figure 9. Thymoma in the cranial mediastinum (white arrows). The internal thoracic artery (black arrow) is also visible.

Mediastinal andpleural mass excision

Selected neoplastic (

e.g.,

thymoma) and inflammatory masses can be removed effectively with a minimally invasive technique (

Figure 9

). Masses that are inoperable with a minimally invasive technique can be evaluated for open surgical resectability or biopsied and staged for appropriate nonsurgical treatment. Patient position and portal placement is determined by the location of the mass. Cranial mediastinal masses are visualized most effectively using a paraxiphoid telescope portal in dorsal recumbency. Bilateral operative portals can be placed with both portals on one side of the thorax. Intercostal space selection for the operative portals depends on the location and size of the cranial mediastinal mass. These portals are placed as ventrally as possible in the appropriate intercostal spaces without traumatizing the internal thoracic artery. Masses are removed using sharp and blunt dissection as indicated with ligatures, vascular clips, and electrosurgical assistance for hemostasis.

Thoracoscopy provides a safe, efficient technique to create pericardial windows and perform lung and pleural biopsies, lung lobectomies, and persistent aortic arch correction in dogs. Animals' recovery after thoracoscopy is superior to that of thoracotomy. The animals are more comfortable, and they require less analgesia. Thoracoscopy also seems to reduce time spent in the hospital.

References

1. Potter, L.; Hendrickson, D.A.: Therapeutic video assisted thoracic surgery.

Vet. Endosurgery

, 1st Ed. (L.J. Freeman, ed.). C.V. Mosby, St. Louis, Mo., 1999; pp 169-191.

2. Kovak, J.R. et al.: Use of thoracoscopy to determine the etiology of pleural effusion in dogs and cats: 18 cases (1998-2001). JAVMA 221:990-994; 2002.

3. Dupre, G.P. et al.: Thoracoscopic pericardectomy performed without pulmonary exclusion in 9 dogs. Vet. Surg. 30:21-27; 2001.

4. Jackson, J. et al.: Thoracoscopic partial pericardiectomy in 13 dogs. J. Vet. Intern. Med. 13:529-533; 1999.

5. Radlinsky, M.G. et al.: Thoracoscopic visualization and ligation of the thoracic duct in dogs. Vet. Surg. 31:138-146; 2002.

6. MacPhail, C.M. et al.: Thoracoscopic correction of persistent right aortic arch in a dog. JAAHA 37:577-581; 2001.

7. Isakow, K. et al.: Video-assisted thoracoscopic division of the ligamentum arteriosum in two dogs with persistent right aortic arch. JAVMA 217:1333-1336; 2000.

8. Lansdown, J.; Monnet, E.: Thoracoscopic lung lobectomy for the treatment of lung tumors in dogs: A review of 9 cases (1999-2003). European College of Veterinary Surgeons, Prague, Czech Republic, 2004.

9. Faunt, K.K. et al.: Evaluation of biopsy specimens obtained during thoracoscopy from lungs of clinically normal dogs. AJVR 59:1499-1502; 1998.

10. Brissot, H.N. et al.: Thoracoscopic treatment of bullous emphysema in 3 dogs. Vet. Surg. 32:524-529; 2003.

11. Lin, J.; Iannettoni, M.D.: The role of thoracoscopy in the management of lung cancer. Surg. Oncol. 12:195-200; 2003.

Eric Monnet, DVM, MS, PhD, DACVS, DECVS, graduated from veterinary school in 1985. A fellow of the American Heart Association, Dr. Monnet is currently an associate professor in small animal surgery (soft tissue) at Colorado State University.