Veterinary Endoscopy
0195-5616/90 $0.00
+ .20
Thoracoscopy Tirrwthy C. McCarthy, DVM, PhD,* and Sharon L. McDerrrwid, CAHTt
Thoracoscopy, or pleuroscopy, is the examination of the chest cavity or pleural cavity with an endoscope. It must be differentiated from mediastinoscopy, which is a commonly employed technique for evaluation of superior mediastinal structures in humans. The cranial mediastinum in the dog has been considered to be too narrow and the pleura too weak for application of true mediastinoscopy. Examination of the pleural cavity is an effective technique that can provide significant diagnostic information with minimal morbidity and mortality. 1 In some respects thoracoscopy is easier to perform than laparoscopy. This technique has been employed in humans for diagnosis and management of spontaneous pneumothorax, pericardia} effusions, neoplasia, and infectious processes involving the pleural space. 2 • 3 • 5 • 7- 9 Application in small animal veterinary medicine has been limited to biopsy collection of pleural lesions. 1 Thoracoscopy has also been employed in the horse for evaluation of pleural effusion, intrathoracic masses, abscesses, and severe pleural adhesions. 4 • 6 INDICATIONS
Diseases that can be diagnosed by thoracoscopy and the complications and contraindications for thoracoscopy are largely undeveloped. The primary indication for thoracoscopy is diagnosis of intrathoracic pathology when direct visualization of the lesions is indicated or desired, when less invasive techniques cannot provide sufficient information, and when surgical invasion of the chest is not indicated or desired. Radiographic and ultrasonographic evaluations revealing mediastinal, pleural, pulmonary, or hilar masses; pleural fluid that cannot be completely removed; and pericardia} fluid are findings that warrant consideration of thoracoscopy. Pleural fluid From the Surgical Specialty Clinic for Animals, Beaverton, Oregon *Diplomate, American College of Veterinary Surgeons; Private Practitioner tCertified Animal Health Technician Veterinary Clinics of North America: Small Animal Practice-Vol. 20, No. 5, September 1990
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loculation can be differentiated from solid tissue masses, and fluid cavities and adhesions can be broken down under direct visualization to allow more complete fluid removal. Biopsies can be taken and samples obtained for bacterial and fungal cultures. Thoracoscopy is far less invasive than surgical exploration and has a much lower morbidity and mortality, yet allows for visual exploration of the thoracic cavity. General anesthesia is required for performing thoracoscopy but the duration and depth of anesthesia are much less than for surgery. In many cases the procedure can be performed and the animal sent home the same day, thus reducing cost and client and patient stress. Many times, the owner's reluctance or desire for surgery plays an important roll in the decision to perform thoracoscopy. With an owner who is reluctant to have surgery performed on a patient, thoracoscopy provides an excellent alternative, allowing the establishment of a diagnosis by which the owner can make decisions about further treatment.
EQUIPMENT The endoscopic instrumentation required for thoracoscopy is the same as that required for laparoscopy. A 5-mm-diameter Olympus laparoscope system (Olympus Corp., Lake Success, NY) has been used for large dogs, and a 2. 7-mm-diameter arthroscope for small dogs and cats. Both of the instrument systems described in this article are designed for application as double-puncture instruments; they do not have biopsy channels and a second puncture of the chest wall must be done for sample collection or manipulation if needed. A Verres's needle is required for initial penetration of the chest wall to avoid lung lobe or vessel laceration by the instrument trochar. Accessory instrumentation includes a trochar and cannula system for passage of the endoscope through the chest wall. The telescopes employed are a 5-mm-diameter laparoscope with a 5-degree viewing angle and a 2. 7-mm-diameter arthroscope with 5- and 25-degree viewing angles. The animal size separation for application of these endoscopes has not been accurately established. The arthroscope system could be applied well to the entire size range of small animal patients from small cats and dogs through the giant breeds. The laparoscope system is better in the larger patients but could be used to a size range of 15 to 20 lb. The primary advantage of the laparoscope in larger patients is the greater light availability for photography. For sample collection and other manipulative procedures a second puncture cannula and trochar are required. The laparoscope system employs a 4.5-mm-diameter cannula and the arthroscope a 3.5mm-cannula. Both cannulae have air seal systems to allow passage and removal of sample collection instrumentation without air leakage. A small 2-mm-diameter apposing cup biopsy forceps is employed with the smaller system, and a 5 X 3 mm cutting jaw biopsy forcep has been used with the larger instrumentation. A wide variety of biopsy forceps are available for application with each size of instrumentation. A smaller version of the cutting jaw biopsy forceps was initially employed with the smaller set of instrumentation; however, it did not have an adequate sample retention
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design, and biopsy samples were easily lost before they could be removed from the chest cavity. The laparoscope system has a specially designed fluid aspiration cannula with multiple holes in the distal 2 em of its tip to allow removal of large quantities of fluid without occlusion. A graduated manipulation probe has been used for retracting and manipulating organs. This probe has 1-cm graduations that allow size assessment. A Menghini needle has been employed infrequently for fluid aspiration from smaller fluid-filled intrathoracic structures and solid masses for cytology. The biopsy instrument most frequently employed for larger intrapulmonary, mediastinal, and hilar masses has been a Tru-Cut biopsy needle. This allows deeper sampling of large masses with less tissue trauma.
PATIENT PREPARATION A thorough preanesthetic assessment of the patient is carried out prior to anesthesia to establish anesthetic risk and to attempt to establish a diagnosis with less invasive procedures. Most of the patients requiring thoracoscopy are older patients, and preanesthetic evaluation should include a blood profile, urinalysis, chest radiographs, and an electrocardiogram. If pleural fluid is present, additional diagnostics for a data base for the thoracic disease should include thoracentesis for fluid analysis and cytology. Pleural drainage will allow improved radiographic imaging and reduced anesthetic risk. Diagnostic ultrasound may also be applicable if the lesion or lesions are situated to allow adequate imaging. After induction of anesthesia, transtracheal washes for cytology and cultures may be indicated. Once it is determined that the patient is a candidate for thoracoscopy, the patient is fasted for 12 hours and anesthesia is induced using a technique acceptable for high-risk or thoracic surgery patients. A cuffed endotracheal tube is required and intermittent positive-pressure breathing is required during a portion of the procedure. The patient is placed in dorsal recumbency or in either lateral recumbent position, depending on the location of the lesion and the area of desired examination. The appropriate area of the chest wall is shaved, scrubbed, and draped in a manner similar to that needed for a thoracotomy. A sufficiently wide area of the chest should be exposed with the draping to allow placement of two chest wall punctures and a chest drain.
TECHNIQUE A site is selected for chest wall puncture that is not directly over the lesion to be examined but is close enough to allow examination of the area of pathology. This offset placement allows passage of the biopsy or other sample collection instrumentation directly over the lesion and still allows visualization and triangulation with the endoscope. A small skin incision is made at the selected site and the Verres's needle is placed through the chest wall into the pleural space. The stop cock on the needle is opened and air is allowed to enter the pleural space until the lungs are partially collapsed. A large amount of lung collapse is not required but sufficient
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needed to allow placement of the endoscope cannula with its trochar without damage to the lung or other thoracic viscera. The amount of pneumothorax can be adjusted after placement of the endoscope. Intermittent positive pressure ventilation is initiated when the pneumothorax is induced. In some patients with compromised ventilatory capacity, initiation of intermittent positive pressure breathing may be desired at the time of anesthetic induction. Patient ventilation may be interrupted periodically during the procedure to allow placement .of the cannula and trochar assemblies and for biopsy or other sample collections. Once an adequate pneumothorax has been created, the Varess needle is removed and the endoscope cannula and trochar are placed through the chest wall at the same location. It is important that placement of the cannula-trochar assembly be done carefully and that excessive depth of placement be prevented to ensure that the thoracic viscera not be damaged. This may be done by using two hands, one on the chest wall around the cannula and the other on the cannula assembly the desired depth of penetration above the first hand. The cannula is forced through the chest wall with the upper hand with a back and forth rotation until it penetrates the chest wall and free motion can be felt. With the hand positions that are used, if the instrumentation breaks through the chest wall suddenly the penetration is stopped when the upper hand hits the lower hand and intrathoracic damage is avoided. The trochar is removed and replaced with the endoscope and the intrathoracic examination is conducted. If sufficient pleural fluid is present to prevent or make adequate examination difficult, it can be removed by passing the aspiration tube through the endoscope cannula or the secondpuncture cannula can be placed. The technique for placement of the biopsy cannula and trochar is the same as for placement of the endoscope cannula. The site for its placement should be selected to allow access to the lesion or lesions for biopsy or other sample collection. Fluid samples can be collected for fluid analysis, cytology, and bacterial and fungal cultures. Fine-needle aspirates can be taken for cytologic examination, and biopsies can be taken for histopathology. Samples can be collected with the special endoscopic instrumentation passed through the second-puncture cannula, or they can be taken with conventional sample collection instrumentation. Tru-Cut biopsy needles work well for collecting biopsy samples from large lung (Fig. 1), mediastinal (Fig. 2), or hilar masses, but they do not work well for smaller masses. With small masses there is a risk of penetration of structures deep to the mass while attempting sample collection. Standard hypodermic needles of sufficient length or the Menghini needle can be used for fluid collection and for fine-needle aspiration. When the examination has been completed the lungs are reexpanded and the instrumentation is removed. The second-puncture cannula is usually removed first and the chest wall closed with one suture in the superficial fascia and one suture in the skin. Positive pressure is applied to the rebreathing system, and the examination cannula is opened to allow exit of air and is closed between insuffiations to prevent recollapse of the lungs between breaths. The extent of lung expansion can be checked by exami-
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Figure 1. Needle biopsy of a large deep papillary adenocarcinoma of the lung in a 10-year-old Saint Bernard.
nation with the endoscope. When re-expansion is nearly complete a chest drain is placed. In cases with minimal or no pleural fluid and no evidence of air leakage, a small drain can be placed through the endoscope cannula. If this is done the drain is placed through the cannula well into the chest and the cannula is removed leaving the chest drain tube in place. The tube is then sutured in place to the skin with 2-0 nylon sutures placed around but not through the tube. Placement of the suture directly around the tube is preferred to attachment with tape butterflies because the tape may loosen and the tube slip. In cases with significant pleural fluid because of the disease process, bleeding, or air leakage secondary to the procedure, a standard chest drain should be placed to allow use of a larger tube. Intermittent positive pressure breathing should be continued until the patient is stable and then a slow transition is made to spontaneous breathing.
Figure 2. Needle biopsy of a large cranial mediastinal mass in a 7-year-old Labrador retriever. Histopathology revealed that the mass was a lymphosarcoma.
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Continuous underwater seal drainage with suction is employed during patient recovery and for a sufficient period to ensure complete lung expansion. Chest radiographs are recommended prior to chest tube removal. Chest tube removal is usually done during anesthetic recovery prior to endotracheal tube removal but may be delayed as indicated by the intrathoracic pathology present. NORMAL ANATOMY
Intrathoracic structures visible endoscopically appear very similar to those seen with an exploratory thoracotomy except where accessibility is limited by the approach used and because of magnification produced by the endoscope. Lateral endoscopic placement allows visualization of the structures of each hemithorax. The ventral approach allows bilateral examination of the chest but is limited to the ventral structures. The exterior surface of the lungs can be seen easily over their exposed surfaces (Fig. 3). The interlobar fissures can be evaluated by displacement of adjacent pulmonary tissue. With endoscopic magnification, close-up observation allows clear visualization of the superficial alveoli (Fig. 4). The internal surface of the chest wall can be well defined with the internal surface of the ribs, muscles, blood vessels, and nerves clearly seen (Fig. 5). The thoracic surface of the diaphragm can be evaluated and the muscular fibers and phrenic nerves can be visualized (Fig. 6). The parietal pleural surfaces are normally smooth and shiny to slightly dull with no visible opacity. The pericardium is opaque, preventing clear visualization of the heart but movement of cardiac structures can be seen. The phrenic and vagal nerves can be seen coursing across the pericardia) surface . On the left side of the thorax, the pulmonary artery and aorta (Fig. 7) can be defined. The major blood vessels of the anterior mediastinum can be located and defined (Fig. 8). The caudal vena cava (Fig. 9) and esophagus can be seen on the right side.
Figure 3. Normal appearance of the pleural surface of the lungs as viewed with the endoscope directed cranially and with the patient in lateral recumbency.
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Figure 4. Normal close-up appearance of the pulmonary surface in a cat demonstrating the superficial alveolar pattern.
Figure 5. Normal appearance of the chest wall showing a rib, intercostal vessels, and intercostal muscles.
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Figure 6. Normal phrenic nerve and pleural surface of the diaphragm.
PATHOLOGY Abnormalities that have been found in the chest by thoracoscopy have included primary and metastatic neoplasia, reactive hilar lymph nodes, pericardia! effusion, and inflammatory tissue associated with a diaphragmatic hernia in a cat. As discussed in the section on normal appearance of the thoracic cavity, there is little difference in the appearance of pathology seen via thoracoscopy and thoracotomy except for magnification produced by the endoscopes and lessened accessibility to a wide area of the chest. Neoplasia The primary limiting factor in visualizing and collecting biopsies of intrathoracic neoplasia is when intrapulmonary masses are small and deep. Superficial pulmonary masses can be seen directly and large deep pulmo-
Figure 7. Normal descending aorta and diaphragmatic lung lobe as viewed from the left side in lateral recumbency.
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Figure 8. Normal appearance of the major vessels of the anterior mediastinum.
nary masses can be located by the overlying atelectasis (Fig. 10). The appearance of pulmonary masses that are seen directly can vary from small white nodules to the large typically variable masses associated with primary lung tumors. Single or multiple lesions may be seen. Mediastinal masses can be seen as large single or multiple masses partially filling the cranial chest (see Fig. 2) or as smaller masses on the pleural surface (Color Plate 0). The variation in appearance, number, size, and location of lesions covers the full spectrum of intrathoracic neoplasia. The number of cases of pleuroscopy that have been performed have not allowed complete definition of the typical appearance of all intrathoracic neoplasia. Spontaneous Pneumothorax One of the causes of spontaneous pneumothorax in the dog is ruptured emphysematous bullae with subsequent air leakage. These lesions can be
Figure 9. Normal caudal vena cava viewed from the right side in a cat.
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Figure 10. Atelectasis superficial to a large deep pulmonary mass.
difficult to locate by noninvasive procedures. Many cases do respond to conservative treatment with chest tubes and underwater seal drainage with continuous or intermittent suction. Those cases that do not respond require surgical correction, usually with pulmonary lobectomy to remove the bullae. Because pulmonary lobectomy is more difficult to perform through a ventral sternotomy incision than through a lateral intercostal thoracotomy, it is desirable to determine the side of involvement prior to surgery. The bullae can usually be visualized via thoracoscopy and thus the side of involvement can be determined. The bullae will appear as air-filled structures protruding from the pulmonary surface (Fig. 11). If the pneumothorax has been of significant duration, extensive atelectasis may also be present (Fig. 12). Hilar Lymph Node Enlargement
A wide variety of conditions can cause enlargement of the hilar lymph nodes. When the hilar lymph nodes are enlarged they can be seen easily
Figure ll. Emphysematous bulla protruding from the lung surface of a 10-year-old mixed breed dog presented with spontaneous pneumothorax.
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Figure 12. Pulmonary atelectasis in the same case as shown in Figure 11.
between the lung lobes, which are partially collapsed for thoracoscopy. The nodes can vary in appearance from normal but large (Fig. 13) to grossly distorted neoplastic masses and can encompass the entire range of appearance of hilar lymph node pathology. Pericardia! Effusion
The large distended pericardia} sac can be defined effectively by thoracoscopy. If visualization is obscured by pleural effusion, the fluid can be drained under direct visualization, allowing the pericardium to be evaluated. The pericardium can be tapped or catheterized and drained also under direct thoracoscopic visualization. With the increased application and availability of ultrasonography and its effectiveness in diagnosis and drainage of pericardia! effusions, the application of thoracoscopy in this disease is limited. Pericardioscopy has been considered as a possible technique for
Figure 13. Enlarged hilar lymph nodes covered with mildly thickened pleura are visible between lung lobes of a 2-year-old male Weimaraner. Histopathology revealed that the enlargement was due to reactive lymph node hyperplasia.
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visualization and biopsy collection of possible pericardia! masses detected with ultrasonography (see Fig. 10) but, to date, has not been attempted. Diaphragmatic Hernia A soft-tissue density in the caudal mediastinum of a cat was evaluated by thoracoscopy. No well-defined mass could be visualized but the caudal portion of the chest was difficult to examine owing to the presence of abnormal tissues. Biopsies revealed chronic .inflammatory tissue. Exploratory surgery revealed a small diaphragmatic hernia.
CONCLUSION There is limited experience in the veterinary profession with thoracoscopy, and there is more to be learned about the indications, pathology, advantages, disadvantages, problems, complications, and contralndications. The authors have not experienced any complications associated with thoracoscopy. Significant hemorrhage or air leakage has not occurred. Thoracoscopy appears to have a significant application for obtaining additional diagnostic information with minimal morbidity and mortality.
REFERENCES 1. Bauer T, Thomas WB: Pulmonary diagnostic techniques. Vet Clin North Am [Small Anim Pract] 13:273-298, 1983 2. Boutin C, Viallat JR, Cargnino P, et al: Thoracoscopic lung biopsy. Chest 82:44-48, 1982 3. Davidson AC, George RJ, Sheldon CD, et al: Thoracoscopy: Assessment of a physician service and comparison of a flexible bronchoscope used as a thoracoscope with a rigid thoracoscope. Thorax 43:327-332, 1988 4. Ford TS, Vaala WE, Sweeney CR, et al: Pleuroscopic diagnosis of gastroesophageal squamous cell carcinoma in a horse. JAm Vet Med Assoc 190:1556-1558, 1987 5. Luther R, Wetzer K, Kuhne W, et al: Asbestos-induced pleural diseases- thoracoscopic aspects. Endoscopy 20:104-106, 1988 6. Mackey VS, Wheat JD: Endoscopic examination of the equine thorax. Equine Vet J 17:140-142, 1985 7. Rodriguez PF, Lopez MJ: Survival time of patients with pleural metastatic carcinoma predicted by glucose and pH studies. Chest 95:320-324, 1989 8. Sarker SK, Purohit SD, Sharma TN, et al: Pleuroscopy in the diagnosis of pleural effusion using a fiberoptic bronchoscope. Tubercle 66:141- 144, 1985 9. Schulz V: Thoracoscopic diagnosis and therapy of spontaneous pneumothorax. Langenbeeks Arch Chir 2 (suppl):493-497, 1988 10. Wong KKS: Use of a flexible choledochoscope for pericardioscopy and drainage of a loculated pericardial effusion. Thorax 42:637-638, 1987
Address reprint requests to Timothy C. McCarthy, DVM, PhD Surgical Specialty Clinic for Animals 4525 SW 109th Avenue Beaverton, OR 97005
0195-5616/90 $0.00
+ .20
Thoracoscopy Tirrwthy C. McCarthy, DVM, PhD,* and Sharon L. McDerrrwid, CAHTt
Thoracoscopy, or pleuroscopy, is the examination of the chest cavity or pleural cavity with an endoscope. It must be differentiated from mediastinoscopy, which is a commonly employed technique for evaluation of superior mediastinal structures in humans. The cranial mediastinum in the dog has been considered to be too narrow and the pleura too weak for application of true mediastinoscopy. Examination of the pleural cavity is an effective technique that can provide significant diagnostic information with minimal morbidity and mortality. 1 In some respects thoracoscopy is easier to perform than laparoscopy. This technique has been employed in humans for diagnosis and management of spontaneous pneumothorax, pericardia} effusions, neoplasia, and infectious processes involving the pleural space. 2 • 3 • 5 • 7- 9 Application in small animal veterinary medicine has been limited to biopsy collection of pleural lesions. 1 Thoracoscopy has also been employed in the horse for evaluation of pleural effusion, intrathoracic masses, abscesses, and severe pleural adhesions. 4 • 6 INDICATIONS
Diseases that can be diagnosed by thoracoscopy and the complications and contraindications for thoracoscopy are largely undeveloped. The primary indication for thoracoscopy is diagnosis of intrathoracic pathology when direct visualization of the lesions is indicated or desired, when less invasive techniques cannot provide sufficient information, and when surgical invasion of the chest is not indicated or desired. Radiographic and ultrasonographic evaluations revealing mediastinal, pleural, pulmonary, or hilar masses; pleural fluid that cannot be completely removed; and pericardia} fluid are findings that warrant consideration of thoracoscopy. Pleural fluid From the Surgical Specialty Clinic for Animals, Beaverton, Oregon *Diplomate, American College of Veterinary Surgeons; Private Practitioner tCertified Animal Health Technician Veterinary Clinics of North America: Small Animal Practice-Vol. 20, No. 5, September 1990
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loculation can be differentiated from solid tissue masses, and fluid cavities and adhesions can be broken down under direct visualization to allow more complete fluid removal. Biopsies can be taken and samples obtained for bacterial and fungal cultures. Thoracoscopy is far less invasive than surgical exploration and has a much lower morbidity and mortality, yet allows for visual exploration of the thoracic cavity. General anesthesia is required for performing thoracoscopy but the duration and depth of anesthesia are much less than for surgery. In many cases the procedure can be performed and the animal sent home the same day, thus reducing cost and client and patient stress. Many times, the owner's reluctance or desire for surgery plays an important roll in the decision to perform thoracoscopy. With an owner who is reluctant to have surgery performed on a patient, thoracoscopy provides an excellent alternative, allowing the establishment of a diagnosis by which the owner can make decisions about further treatment.
EQUIPMENT The endoscopic instrumentation required for thoracoscopy is the same as that required for laparoscopy. A 5-mm-diameter Olympus laparoscope system (Olympus Corp., Lake Success, NY) has been used for large dogs, and a 2. 7-mm-diameter arthroscope for small dogs and cats. Both of the instrument systems described in this article are designed for application as double-puncture instruments; they do not have biopsy channels and a second puncture of the chest wall must be done for sample collection or manipulation if needed. A Verres's needle is required for initial penetration of the chest wall to avoid lung lobe or vessel laceration by the instrument trochar. Accessory instrumentation includes a trochar and cannula system for passage of the endoscope through the chest wall. The telescopes employed are a 5-mm-diameter laparoscope with a 5-degree viewing angle and a 2. 7-mm-diameter arthroscope with 5- and 25-degree viewing angles. The animal size separation for application of these endoscopes has not been accurately established. The arthroscope system could be applied well to the entire size range of small animal patients from small cats and dogs through the giant breeds. The laparoscope system is better in the larger patients but could be used to a size range of 15 to 20 lb. The primary advantage of the laparoscope in larger patients is the greater light availability for photography. For sample collection and other manipulative procedures a second puncture cannula and trochar are required. The laparoscope system employs a 4.5-mm-diameter cannula and the arthroscope a 3.5mm-cannula. Both cannulae have air seal systems to allow passage and removal of sample collection instrumentation without air leakage. A small 2-mm-diameter apposing cup biopsy forceps is employed with the smaller system, and a 5 X 3 mm cutting jaw biopsy forcep has been used with the larger instrumentation. A wide variety of biopsy forceps are available for application with each size of instrumentation. A smaller version of the cutting jaw biopsy forceps was initially employed with the smaller set of instrumentation; however, it did not have an adequate sample retention
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design, and biopsy samples were easily lost before they could be removed from the chest cavity. The laparoscope system has a specially designed fluid aspiration cannula with multiple holes in the distal 2 em of its tip to allow removal of large quantities of fluid without occlusion. A graduated manipulation probe has been used for retracting and manipulating organs. This probe has 1-cm graduations that allow size assessment. A Menghini needle has been employed infrequently for fluid aspiration from smaller fluid-filled intrathoracic structures and solid masses for cytology. The biopsy instrument most frequently employed for larger intrapulmonary, mediastinal, and hilar masses has been a Tru-Cut biopsy needle. This allows deeper sampling of large masses with less tissue trauma.
PATIENT PREPARATION A thorough preanesthetic assessment of the patient is carried out prior to anesthesia to establish anesthetic risk and to attempt to establish a diagnosis with less invasive procedures. Most of the patients requiring thoracoscopy are older patients, and preanesthetic evaluation should include a blood profile, urinalysis, chest radiographs, and an electrocardiogram. If pleural fluid is present, additional diagnostics for a data base for the thoracic disease should include thoracentesis for fluid analysis and cytology. Pleural drainage will allow improved radiographic imaging and reduced anesthetic risk. Diagnostic ultrasound may also be applicable if the lesion or lesions are situated to allow adequate imaging. After induction of anesthesia, transtracheal washes for cytology and cultures may be indicated. Once it is determined that the patient is a candidate for thoracoscopy, the patient is fasted for 12 hours and anesthesia is induced using a technique acceptable for high-risk or thoracic surgery patients. A cuffed endotracheal tube is required and intermittent positive-pressure breathing is required during a portion of the procedure. The patient is placed in dorsal recumbency or in either lateral recumbent position, depending on the location of the lesion and the area of desired examination. The appropriate area of the chest wall is shaved, scrubbed, and draped in a manner similar to that needed for a thoracotomy. A sufficiently wide area of the chest should be exposed with the draping to allow placement of two chest wall punctures and a chest drain.
TECHNIQUE A site is selected for chest wall puncture that is not directly over the lesion to be examined but is close enough to allow examination of the area of pathology. This offset placement allows passage of the biopsy or other sample collection instrumentation directly over the lesion and still allows visualization and triangulation with the endoscope. A small skin incision is made at the selected site and the Verres's needle is placed through the chest wall into the pleural space. The stop cock on the needle is opened and air is allowed to enter the pleural space until the lungs are partially collapsed. A large amount of lung collapse is not required but sufficient
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needed to allow placement of the endoscope cannula with its trochar without damage to the lung or other thoracic viscera. The amount of pneumothorax can be adjusted after placement of the endoscope. Intermittent positive pressure ventilation is initiated when the pneumothorax is induced. In some patients with compromised ventilatory capacity, initiation of intermittent positive pressure breathing may be desired at the time of anesthetic induction. Patient ventilation may be interrupted periodically during the procedure to allow placement .of the cannula and trochar assemblies and for biopsy or other sample collections. Once an adequate pneumothorax has been created, the Varess needle is removed and the endoscope cannula and trochar are placed through the chest wall at the same location. It is important that placement of the cannula-trochar assembly be done carefully and that excessive depth of placement be prevented to ensure that the thoracic viscera not be damaged. This may be done by using two hands, one on the chest wall around the cannula and the other on the cannula assembly the desired depth of penetration above the first hand. The cannula is forced through the chest wall with the upper hand with a back and forth rotation until it penetrates the chest wall and free motion can be felt. With the hand positions that are used, if the instrumentation breaks through the chest wall suddenly the penetration is stopped when the upper hand hits the lower hand and intrathoracic damage is avoided. The trochar is removed and replaced with the endoscope and the intrathoracic examination is conducted. If sufficient pleural fluid is present to prevent or make adequate examination difficult, it can be removed by passing the aspiration tube through the endoscope cannula or the secondpuncture cannula can be placed. The technique for placement of the biopsy cannula and trochar is the same as for placement of the endoscope cannula. The site for its placement should be selected to allow access to the lesion or lesions for biopsy or other sample collection. Fluid samples can be collected for fluid analysis, cytology, and bacterial and fungal cultures. Fine-needle aspirates can be taken for cytologic examination, and biopsies can be taken for histopathology. Samples can be collected with the special endoscopic instrumentation passed through the second-puncture cannula, or they can be taken with conventional sample collection instrumentation. Tru-Cut biopsy needles work well for collecting biopsy samples from large lung (Fig. 1), mediastinal (Fig. 2), or hilar masses, but they do not work well for smaller masses. With small masses there is a risk of penetration of structures deep to the mass while attempting sample collection. Standard hypodermic needles of sufficient length or the Menghini needle can be used for fluid collection and for fine-needle aspiration. When the examination has been completed the lungs are reexpanded and the instrumentation is removed. The second-puncture cannula is usually removed first and the chest wall closed with one suture in the superficial fascia and one suture in the skin. Positive pressure is applied to the rebreathing system, and the examination cannula is opened to allow exit of air and is closed between insuffiations to prevent recollapse of the lungs between breaths. The extent of lung expansion can be checked by exami-
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Figure 1. Needle biopsy of a large deep papillary adenocarcinoma of the lung in a 10-year-old Saint Bernard.
nation with the endoscope. When re-expansion is nearly complete a chest drain is placed. In cases with minimal or no pleural fluid and no evidence of air leakage, a small drain can be placed through the endoscope cannula. If this is done the drain is placed through the cannula well into the chest and the cannula is removed leaving the chest drain tube in place. The tube is then sutured in place to the skin with 2-0 nylon sutures placed around but not through the tube. Placement of the suture directly around the tube is preferred to attachment with tape butterflies because the tape may loosen and the tube slip. In cases with significant pleural fluid because of the disease process, bleeding, or air leakage secondary to the procedure, a standard chest drain should be placed to allow use of a larger tube. Intermittent positive pressure breathing should be continued until the patient is stable and then a slow transition is made to spontaneous breathing.
Figure 2. Needle biopsy of a large cranial mediastinal mass in a 7-year-old Labrador retriever. Histopathology revealed that the mass was a lymphosarcoma.
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Continuous underwater seal drainage with suction is employed during patient recovery and for a sufficient period to ensure complete lung expansion. Chest radiographs are recommended prior to chest tube removal. Chest tube removal is usually done during anesthetic recovery prior to endotracheal tube removal but may be delayed as indicated by the intrathoracic pathology present. NORMAL ANATOMY
Intrathoracic structures visible endoscopically appear very similar to those seen with an exploratory thoracotomy except where accessibility is limited by the approach used and because of magnification produced by the endoscope. Lateral endoscopic placement allows visualization of the structures of each hemithorax. The ventral approach allows bilateral examination of the chest but is limited to the ventral structures. The exterior surface of the lungs can be seen easily over their exposed surfaces (Fig. 3). The interlobar fissures can be evaluated by displacement of adjacent pulmonary tissue. With endoscopic magnification, close-up observation allows clear visualization of the superficial alveoli (Fig. 4). The internal surface of the chest wall can be well defined with the internal surface of the ribs, muscles, blood vessels, and nerves clearly seen (Fig. 5). The thoracic surface of the diaphragm can be evaluated and the muscular fibers and phrenic nerves can be visualized (Fig. 6). The parietal pleural surfaces are normally smooth and shiny to slightly dull with no visible opacity. The pericardium is opaque, preventing clear visualization of the heart but movement of cardiac structures can be seen. The phrenic and vagal nerves can be seen coursing across the pericardia) surface . On the left side of the thorax, the pulmonary artery and aorta (Fig. 7) can be defined. The major blood vessels of the anterior mediastinum can be located and defined (Fig. 8). The caudal vena cava (Fig. 9) and esophagus can be seen on the right side.
Figure 3. Normal appearance of the pleural surface of the lungs as viewed with the endoscope directed cranially and with the patient in lateral recumbency.
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Figure 4. Normal close-up appearance of the pulmonary surface in a cat demonstrating the superficial alveolar pattern.
Figure 5. Normal appearance of the chest wall showing a rib, intercostal vessels, and intercostal muscles.
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Figure 6. Normal phrenic nerve and pleural surface of the diaphragm.
PATHOLOGY Abnormalities that have been found in the chest by thoracoscopy have included primary and metastatic neoplasia, reactive hilar lymph nodes, pericardia! effusion, and inflammatory tissue associated with a diaphragmatic hernia in a cat. As discussed in the section on normal appearance of the thoracic cavity, there is little difference in the appearance of pathology seen via thoracoscopy and thoracotomy except for magnification produced by the endoscopes and lessened accessibility to a wide area of the chest. Neoplasia The primary limiting factor in visualizing and collecting biopsies of intrathoracic neoplasia is when intrapulmonary masses are small and deep. Superficial pulmonary masses can be seen directly and large deep pulmo-
Figure 7. Normal descending aorta and diaphragmatic lung lobe as viewed from the left side in lateral recumbency.
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Figure 8. Normal appearance of the major vessels of the anterior mediastinum.
nary masses can be located by the overlying atelectasis (Fig. 10). The appearance of pulmonary masses that are seen directly can vary from small white nodules to the large typically variable masses associated with primary lung tumors. Single or multiple lesions may be seen. Mediastinal masses can be seen as large single or multiple masses partially filling the cranial chest (see Fig. 2) or as smaller masses on the pleural surface (Color Plate 0). The variation in appearance, number, size, and location of lesions covers the full spectrum of intrathoracic neoplasia. The number of cases of pleuroscopy that have been performed have not allowed complete definition of the typical appearance of all intrathoracic neoplasia. Spontaneous Pneumothorax One of the causes of spontaneous pneumothorax in the dog is ruptured emphysematous bullae with subsequent air leakage. These lesions can be
Figure 9. Normal caudal vena cava viewed from the right side in a cat.
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Figure 10. Atelectasis superficial to a large deep pulmonary mass.
difficult to locate by noninvasive procedures. Many cases do respond to conservative treatment with chest tubes and underwater seal drainage with continuous or intermittent suction. Those cases that do not respond require surgical correction, usually with pulmonary lobectomy to remove the bullae. Because pulmonary lobectomy is more difficult to perform through a ventral sternotomy incision than through a lateral intercostal thoracotomy, it is desirable to determine the side of involvement prior to surgery. The bullae can usually be visualized via thoracoscopy and thus the side of involvement can be determined. The bullae will appear as air-filled structures protruding from the pulmonary surface (Fig. 11). If the pneumothorax has been of significant duration, extensive atelectasis may also be present (Fig. 12). Hilar Lymph Node Enlargement
A wide variety of conditions can cause enlargement of the hilar lymph nodes. When the hilar lymph nodes are enlarged they can be seen easily
Figure ll. Emphysematous bulla protruding from the lung surface of a 10-year-old mixed breed dog presented with spontaneous pneumothorax.
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Figure 12. Pulmonary atelectasis in the same case as shown in Figure 11.
between the lung lobes, which are partially collapsed for thoracoscopy. The nodes can vary in appearance from normal but large (Fig. 13) to grossly distorted neoplastic masses and can encompass the entire range of appearance of hilar lymph node pathology. Pericardia! Effusion
The large distended pericardia} sac can be defined effectively by thoracoscopy. If visualization is obscured by pleural effusion, the fluid can be drained under direct visualization, allowing the pericardium to be evaluated. The pericardium can be tapped or catheterized and drained also under direct thoracoscopic visualization. With the increased application and availability of ultrasonography and its effectiveness in diagnosis and drainage of pericardia! effusions, the application of thoracoscopy in this disease is limited. Pericardioscopy has been considered as a possible technique for
Figure 13. Enlarged hilar lymph nodes covered with mildly thickened pleura are visible between lung lobes of a 2-year-old male Weimaraner. Histopathology revealed that the enlargement was due to reactive lymph node hyperplasia.
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visualization and biopsy collection of possible pericardia! masses detected with ultrasonography (see Fig. 10) but, to date, has not been attempted. Diaphragmatic Hernia A soft-tissue density in the caudal mediastinum of a cat was evaluated by thoracoscopy. No well-defined mass could be visualized but the caudal portion of the chest was difficult to examine owing to the presence of abnormal tissues. Biopsies revealed chronic .inflammatory tissue. Exploratory surgery revealed a small diaphragmatic hernia.
CONCLUSION There is limited experience in the veterinary profession with thoracoscopy, and there is more to be learned about the indications, pathology, advantages, disadvantages, problems, complications, and contralndications. The authors have not experienced any complications associated with thoracoscopy. Significant hemorrhage or air leakage has not occurred. Thoracoscopy appears to have a significant application for obtaining additional diagnostic information with minimal morbidity and mortality.
REFERENCES 1. Bauer T, Thomas WB: Pulmonary diagnostic techniques. Vet Clin North Am [Small Anim Pract] 13:273-298, 1983 2. Boutin C, Viallat JR, Cargnino P, et al: Thoracoscopic lung biopsy. Chest 82:44-48, 1982 3. Davidson AC, George RJ, Sheldon CD, et al: Thoracoscopy: Assessment of a physician service and comparison of a flexible bronchoscope used as a thoracoscope with a rigid thoracoscope. Thorax 43:327-332, 1988 4. Ford TS, Vaala WE, Sweeney CR, et al: Pleuroscopic diagnosis of gastroesophageal squamous cell carcinoma in a horse. JAm Vet Med Assoc 190:1556-1558, 1987 5. Luther R, Wetzer K, Kuhne W, et al: Asbestos-induced pleural diseases- thoracoscopic aspects. Endoscopy 20:104-106, 1988 6. Mackey VS, Wheat JD: Endoscopic examination of the equine thorax. Equine Vet J 17:140-142, 1985 7. Rodriguez PF, Lopez MJ: Survival time of patients with pleural metastatic carcinoma predicted by glucose and pH studies. Chest 95:320-324, 1989 8. Sarker SK, Purohit SD, Sharma TN, et al: Pleuroscopy in the diagnosis of pleural effusion using a fiberoptic bronchoscope. Tubercle 66:141- 144, 1985 9. Schulz V: Thoracoscopic diagnosis and therapy of spontaneous pneumothorax. Langenbeeks Arch Chir 2 (suppl):493-497, 1988 10. Wong KKS: Use of a flexible choledochoscope for pericardioscopy and drainage of a loculated pericardial effusion. Thorax 42:637-638, 1987
Address reprint requests to Timothy C. McCarthy, DVM, PhD Surgical Specialty Clinic for Animals 4525 SW 109th Avenue Beaverton, OR 97005
