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Thoracoscopic Lung Biopsy and Lung Lobectomy
Eric Monnet
Lung biopsy and lung lobectomy can be performed with video-assisted thoracoscopic surgery (VATS) in dogs. The minimal invasiveness of the procedure, the rapid patient recovery, and diagnostic accuracy make VATS an ideal technique over other more invasive procedures for the resection of small primary lung tumors. It can also be used for surgical treatment of spontaneous pneumothorax. Diffuse lung disease may require the collection of a peripheral lung biopsy for culture and histology. Lung biopsy can be collected with VATS with minimal morbidity for the patient. Also, lymph node biopsies for staging purposes can be collected at the same time.
Complete or partial lung lobectomy can be completed under VATS or with a thoracoscopic-assisted procedure. One-lung ventilation (OLV) may be required for lung lobectomy.
Preoperative Considerations
Patient Selection
Thoracoscopic or thoracoscopic-assisted resection of lung disease is especially appropriate for the resection of small lung lesions at the periphery of the lung lobes (Figures 32.1 and 32.2).1,2 Primary lung tumor is the most common indication for lung lobectomy, but resection of single lung metastasis has also been performed.
Figure 32.1 Radiograph of a dog with a solitary lung mass in the right middle lung lobe. The mass is small and located peripheral to the hilus, making it an ideal case for thoracoscopic lung lobectomy.
Figure 32.2 Computed tomography of the same mass as in Figure 32.1.
Adenocarcinomas are the most commonly reported lung tumors in dogs.3-5 Squamous cell carcinomas and anaplastic carcinoma are less frequently seen in dogs.4 Primary mesenchymal lung neoplasms, osteosarcoma, fibrosarcoma, and hemangiosarcoma are rarely reported in dogs and cats.4 In young dogs, benign lymphomatous granulomatosis has been reported; however, they are very rare. Malignant histiocytosis is a large tumor which metastasize very quickly; it is reported most commonly in Bernese mountain dog. Primary lung tumors are usually aggressive tumors that metastasize to the lungs, lymph nodes, and pleural space.6-8 They have been reported to metastasize to the skeletal muscles, liver, kidney, and heart.9 Transitional cell carcinoma, hemangiosarcoma, thyroid carcinoma, melanoma, and osteosarcoma have a tendency to metastasize to the lungs.
Dogs with primary lung tumors are on average 10 to 12 years of age, and no sex or breed predisposition has been reported. Dogs with primary lung tumors are asymptomatic early in the disease process. Lethargy, inappetence, weight loss, and exercise intolerance could be present in dogs with primary lung tumors. Nonproductive cough can be reported by the owners. Hypertrophic osteopathy inducing severe lameness has been observed in several dogs with primary lung tumors.3 Lung sounds may be decreased at the level of the lung mass or if effusion is present in the pleural space.
Three-view radiographs are required for the diagnosis of primary lung tumors and identification of metastasis.3 Primary lung tumors more commonly appear as a one solid mass in a caudal lung lobe but may occur in any lung lobe (see Figure 32.1). Computed tomography (CT) is another alternative to further identify primary lung tumors, small metastasis, and lymph node involvement (see Figure 32.2).10,11
The size of the tumor (<5 cm), lymph node involvement, and clean margin at the time of surgery have been established as determinants for long-term outcome in dogs with primary lung tumors.5,12 The median survival time was 26 days for dogs with lymph node involvement versus 452 days without lymph node involvement in a study on 67 cases of primary lung tumor in dogs.5 Dogs with a well-differentiated tumor had longer survival time (790 days) than dogs with a poorly differentiated tumor (5 days).5 The tumor stage is also a prognostic indicator with T1 (solitary noninvasive) tumor having a 790-day median survival time and T3 (locally invasive) tumor 81 days.5 The median survival time for adenocarcinoma was 19 months versus 8 months for squamous cell carcinoma.13
In a mass larger than 5 to 7 cm in diameter, VATS is of questionable value because a large thoracotomy at the end of the surgery is required for tumor extraction, and the benefit of the minimally invasive approach will be lost. Dogs with a large mass in the lung parenchyma or a mass close to the hilus are not good candidates for thoracoscopic surgery. A large mass makes the manipulation required for lung hilus visualization and staples placement difficult. Also, if the mass is close to the hilus, safe placement of staples is difficult.1 In addition, a clean margin might be difficult to obtain if the mass is located close to the hilus. A thoracoscopic-assisted procedure can be performed but the thoracotomy to extract the lung lobe has to be large enough to safely remove the lung lobe.
Spontaneous pneumothorax occurs in dogs without evidence of trauma. Spontaneous pneumothorax caused by a ruptured lung bullae can be explored and treated with VATS.14 However, an evaluation of the entire lung parenchyma is not always possible with either a transdiaphragmatic or an intercostal approach, making the utilization of VATS for treatment of spontaneous pneumothorax questionable.
Diagnosis and Imaging
Exploration of the entire lung parenchyma can be very challenging in dogs even with OLV. CT has been used for localizing bullae and bleb,15,16 but the ruptured bullae or bleb may not be visible if located in atelectatic tissue.
In dogs with lung tumor, the size and location of the mass are important criteria for selection of patients. Therefore, thoracic radiographs and CT of the thorax are important imaging modalities. For tumors in the cranial lung lobe, it can be difficult to determine if the mass is in the left or right cranial lung lobe on radiographic examination. Therefore, CT may help to further define the location of the mass and in deciding the side for intercostal VATS.10
A CT scan will also help to evaluate the hilar lymph nodes. If any hilar lymph node looks reactive on CT scan, an effort to biopsy it during VATS will be important (Figure 32.3). Lymph node metastasis is an important prognostic indicator for long-term survival.5,12
Figure 32.3 Biopsy of hilar lymph nodes are often indicated in dogs with video-assisted thoracoscopic surgery lung lobectomy.
Patient Evaluation and Preparation
Patient Preparation
Spontaneous pneumothorax is usually severe and requires placement of a thoracostomy tube for effective treatment before surgery. Continuous pleural suction is often necessary to keep the pleural space evacuated, especially in the early treatment period. After evacuation of the pleural space, thoracic radiographs, including both lateral views, and CT scan should be examined for primary or secondary causes of pneumothorax. Pulmonary bullae may be visible on thoracic radiographs. Pulmonary blebs usually are not visible.15,16
Creation of Working Space: One-Lung Ventilation
One-lung ventilation is important for performance of lung lobectomy. OLV improves visualization of the mass and the hilus of the lungs and increases the amount of space in the thoracic cavity available for instrumentation (Figure 32.4). Stapling equipment is used during lung lobectomy or lung biopsy and requires a large space for instrument manipulation.
Figure 32.4 Intraoperative view of a mass in the left caudal lung lobe. The lung parenchyma is not inflated around the mass because of one-lung ventilation.
One-lung ventilation can be achieved with different procedures. Selective intubation of the lung lobe that will remain ventilated, with either a double-lumen endotracheal tube or a long endotracheal tube, has been used.17,18 Use of a double-lumen endotracheal tube allows for selective or alternating ventilation of the left or right lung lobes. This technique has mostly been used for resection of cranial mediastinal masses or subtotal pericardectomy.17-19 Placement of an endobronchial blocker to exclude the lung lobe to be resected is another option.20 Both techniques require a bronchoscope for correct placement of the double-lumen endotracheal tube or the endobronchial blocker. When an endobronchial blocker is used, it is important to inflate the balloon at the end of the blocker appropriately. If the balloon is not inflated enough, it may create a one-way valve, allowing oxygen to pass around the balloon during positive-pressure ventilation but not allowing gas escape passively during expiration. Consequently, overinflation of the lung may lead to barotrauma.
One-lung ventilation induces atelectasis of the nonventilated (dependent) lung, which result in a ventilation/perfusion (V/Q) mismatch with hypoxemia.20,21 The dependent lung receives more blood flow than the nondependent one because of the patient’s lateral recumbency for most of the lung lobectomy, leading to a low V/Q ratio. Conversely, the dependent lung is in a high V/Q situation, which cannot compensate for the low V/Q situation of the nondependent lung. The dependent lung under the pressure of the heart will gradually get atelectatic, which exacerbates the hypoxemia.20,21
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