Specialty Spotlight: Minimally Invasive Surgery for Management of Lung Tumors

Minimally Invasive Surgery for Management of Lung Tumors
Joseph Palamara, DVM, DACVS-SA

Minimally invasive surgery is a constantly evolving field of veterinary surgery. Competency and expertise in minimally invasive surgery are requirements in the process of board certification in small animal surgery. Thoracoscopy, laparoscopy and arthroscopy are minimally invasive procedures which involve surgery of the chest, abdomen and joints, respectively. Advances in technology adapted from human surgery and innovations developed by veterinary surgeons have enabled a wide array of surgical capabilities to offer an ever-expanding list of surgical applications in veterinary medicine. Veterinary literature supports the use of minimally invasive surgery in prophylactic, diagnostic and therapeutic surgical procedures. Patients benefit from these techniques, experiencing smaller incisions, less pain, shorter hospitalization periods and overall quicker recoveries.

Thoracoscopy involves the use of cannulas and ports to allow safe passage of cameras, small instruments and stapling devices to conduct surgery of the chest cavity involving the lungs, heart, lymph nodes, and lymphatics. One specific application is the use of thoracoscopy to treat tumors of the lung in dogs and cats. Lung tumors in dogs and cats occur with less frequency than people. Dogs and cats affected with pulmonary tumors are typically over 11 years of age. Lung tumors are typically found incidentally during geriatric screening where up to 30% of cases of primary pulmonary tumors will be diagnosed without the presence of clinical signs. The most common clinical signs of pulmonary tumors in dogs and cats include coughing, difficulty breathing, lethargy, decreased appetite, weight loss or coughing with the presence of blood. Additionally, cats may also present with gastrointestinal symptoms like vomiting, regurgitation and diarrhea. Routine staging always begins with a thorough physical examination, including rectal examination, along with serum biochemistry, complete blood count, and urinalysis (cystocentesis if possible). Three view thoracic radiographs are standard for an initial workup of any suspicious lung lesions. Thoracic ultrasound may be used to assess lung or obtain a sample of tissue via fine-needle aspirate. Thoracic CT (computed topography) is a more accurate test which allows evaluation of tracheobronchial lymph nodes (TBLN) and is more sensitive in detecting pulmonary nodules when compared to radiographs. Enlargement of TBLNs or evidence of pulmonary nodules in more than one lung lobe increases the likelihood of metastases and imparts a poor prognosis. Additional staging includes evaluation of the abdomen for evidence of primary malignancy by way of abdominal ultrasound or contrast abdominal CT. Patients determined to have a solitary lung tumor (primarily affecting the lung) with no evidence of metastatic disease are considered good candidates for surgery.

Open thoracotomy is the standard of care for primary lung tumors to remove a portion or all of an affected lung lobe. Traditional surgery for lung tumors typically involves intercostal thoracotomy or median sternotomy.  Minimally invasive thoracic surgery [thoracoscopy and video-assisted thoracoscopic surgery (VATS)] has become a widely accepted option for thoracic surgery in dogs and cats. The use of cannulas and a limited intercostal thoracotomy overall reduce pain and morbidity by reducing transection of muscles to gain entry while providing acceptable exposure for proper cavity exploration. Small (< 5cm) and peripheral lung tumors are most amenable to minimally invasive techniques. Occasionally patients with larger and hilar lung tumors may be candidates. The goal is a clean resection with at least 1 cm (preferably 2 cm) of clean tissue. Contrast CT is used to create a three-dimensional image (Figure 1) to define tumor location with respect to adjacent lung lobes and blood supply. The optimal working intercostal space and port locations are determined to assist in creating an individualized patient plan (Figure 2). A camera port is placed to allow cavity visualization. Two to three additional instrument ports are placed to triangulate around the site of interest to allow efficient thoracic exploration, retract structures, and manipulate the affected lung (Figure 2). Tracheobronchial lymph node extirpation (removal of the entire lymph node) is performed using bipolar technology to allow evaluation of the local lymph node(s) via histopathology. Based on the preoperative plan and intraoperative findings, final determination of the level of resection is made – partial or total lung removal. Complete caudal lung lobectomy requires transection of the pulmonary ligament which loosely tethers the lung to the mediastinum (Figure 3). The affected lung is suspended with atraumatic forceps while additional instruments are used to retract adjacent lung lobes to provide optimal visualization of the proposed removal site. A roticulating ENDO GIA (Figure 4) is introduced with articulation up to 45 degrees, simultaneously ligating the affected lung with six rows of staples and transecting/dividing between the center staple line. The transected lung tumor is then retrieved via a specimen bag to limit tumor cell exposure to the pleural cavity. The cannula site is enlarged or extended (mini-thoracotomy) to allow removal of the lung tumor. Additionally, wound retractors provide a nice complement to circumferential intercostal retraction. The remaining lung or pulmonary hilus is then inspected for air or blood leakage. The thorax is lavaged with warmed sterile saline and suctioned. A temporary thoracostomy tube is placed and maintained for 12 to 24 hours. The incisions are closed; larger incisions may benefit from local blocks with bupicivaine, lidocaine, or extended-release bupivicaine (Nocita®). The histopathologic samples are placed in formalin and submitted. Patients are typically discharged within 24 to 72 hours of surgery and are rechecked at 2 weeks post-surgery.  Most patients return to normal activity within 2 to 3 weeks of surgery.

Overall prognosis and median survival time for patients undergoing removal of primary lung tumors is reported around 361 days. Prognostic factors include the presence of clinical signs, clinical stage, tumor size, tumor type and histologic grade. Withrow and MacEwen’s Small Animal Clinical Oncology states:

Dogs with clinical signs associated with a primary lung tumor had an MST of 240 days compared with 545 days for asymptomatic dogs. Dogs with single solitary lung tumors (T1 clinical stage) had an MST of 790 days, which was significantly longer than dogs with multiple lung tumors (T2 clinical stage, 196 days) and dogs with lung tumors invading into adjacent structures (T3 clinical stage, 81 days).[1] Finally, the MST for dogs with grade I lung carcinomas was 790 days, and this was significantly longer than the MSTs of 251 days and 5 days for dogs with grade II and III lung carcinomas, respectively.

Most patients will benefit from a medical oncology consultation to discuss need for adjuvant therapy. Patients with aggressive tumors or metastatic disease may benefit with adjuvant chemotherapy or palliative therapy techniques offered by our medical oncology team. A combination surgical and oncological multi-specialty approach provides clients with the most current treatments options to help patients live longer and healthier lives.

Upstate Veterinary Specialties is proud to offer consultation to clients for minimally invasive surgery (thoracoscopy, laparoscopy and arthroscopy) services and adjuvant medical oncology options for clients and their pets.

– Joseph Palamara, DVM, DACVS-SA

[1] The TNM Staging System is based on the extent of the tumor (T), the extent of spread to the lymph nodes (N), and the presence of metastasis (M)