LUNG LOBE TUMORS
Overview of the Condition
In dogs and cats, lung lobe (“pulmonary”) tumors are most frequently a result of cancer cells that have been carried by the blood stream and into the lung tissue. These types of tumors are called “metastatic”. Primary lung lobe tumors — tumors that originate in the lung tissue — are much less common. Most come from glandular structures (“adenocarcinoma”), but they can also come from portions of the lung tissue that provide support (“fibrosarcoma” from fibrous tissue, or “chondrosarcoma” from cartilage), blood vessels (“hemangiosarcoma”), and other structures.
Dogs and cats that present with primary lung tumors are usually middle age or older. About 25% of animals with a primary lung tumor will have no signs; these animals may have tumors found incidentally when chest x-rays are taken for some other reason. Some animals will present with a cough, weight loss, or lethargy. Tumors that are large or compress vital structures can cause difficulty breathing or regurugitation- where food comes back up suddenly after eating. Some animals may have lameness because the lung lobe tumor has spread to other sites or has caused swelling and bony reaction along the toes and lower bones of the leg (“hypertrophic osteopathy”).
Dogs that live in a household with smokers, or in environments high in some pollutants, such as asbestos, are at an increased risk for primary lung lobe tumors. Brachycephalic breeds, with their flat noses, are also at a greater risk than long nosed breeds.
Lung tumors are diagnosed on x-rays or CT of the chest (Figures 1, 2). They are hard to see on x-ray until they are at least a half inch in diameter. Tumors that are large or close to the chest wall can be sampled with a needle and syringe; the samples are then examined under a microscope to determine type of tumor. Because most animals are older when they are affected, their blood work and urine are evaluated for evidence of other illnesses.
Figure 1. Lung lobe tumor (black arrows) in one of the caudal (rear) lung lobes of a dog.
Figure 2. This lung lobe tumor measured 47.8 mm (almost 2 inches) in diameter.
Figure 3. A CT scan of a dog’s chest is being performed to see if the lungs have more than one tumor.
Abcesses and fungal masses within the lung tissue can look similar on x-rays; however, they are much less common than tumors. Lung lobes can sometimes twist (“lung lobe torsion”), causing coughing and difficulty breathing, but the appearance on x-ray is usually different from a lung tumor.
Single lung lobe tumors are removed surgically, either through a large incision in the side of the chest, or through several smaller incisions with the help of a laparoscope. Multiple lung lobe tumors are usually metastatic- cancer spread from another site- and treated with chemotherapy.
Cats and dogs have 2 lungs- the right and left- and each lung is divided into several lobes that can be removed separately. Most lung lobe tumors are removed through an incision in the side of the chest (“thoracotomy”), just behind the front leg. The incision goes between the ribs, which are spread apart and then brought back together once the lung lobe has been removed. The blood vessels and air tube (“bronchus”) to the lobe are either tied off with suture or with a stapler. Staplers are usually used by ACVS Veterinary Surgeons since they are much faster and easier than suture closures.
Figure 4. A 2 inch lung lobe tumor in a caudal (rear) lung lobe. A black silk suture has been passed around the large artery to the lobe.
Figure 5. The ribs have been spread apart to expose a lung lobe tumor in a middle lung lobe. A stapler is resting on the dog’s chest, ready for use.
Figure 6. The stapler has been placed across the lung lobe and, when the trigger is squeezed, 3 rows of staplers will seal the end of the lobe.
Figure 7. Appearance of the site after the lobe has been stapled off and removed.
A chest tube is placed to remove any fluid or air from the chest cavity after surgery and for infusion of local anesthetic to reduce pain. Chest tubes are usually kept in for 12 to 24 hours after the surgery. Since these surgeries are very painful, multiple types of pain preventatives and treatment may be used, including epidural anesthesia (injection of pain medication around the spinal cord); intravenous drugs; fentanyl patches (a patch that delivers drugs through the skin); and tablets or liquid when the animal is awake.
Figure 8. This chest tube is being used to remove excess fluid or air and to instill a local anesthetic to block pain.
When to Seek Referral
Because animals with lung tumors have compromised airways, special care is needed before, during, and after surgery. Practices should have a specialist in anesthesia and pain management, and surgery by an ACVS Veterinary Surgeon is recommended because of the skill and speed required for the procedure. Find an ACVS Veterinary Surgeon.
Potential Complications of Surgery
Anesthesia can be risky in any older animal, but the risk increases in animals whose airways are diseased. Many animals must be placed on ventilators during the surgery to keep them well oxygenated. Fluid may pour out of the tumor airway during surgery, blocking the other airways or causing pneumonia. Bleeding or air leakage can be a potential problem if the blood vessels or bronchus do not seal properly. Pain medications are necessary for several days after the surgery; patients that are painful will not expand their lungs well and could suffer from low oxygen. Despite these potential complications, most dogs and cats survive the surgery.
Because the surgery site is directly behind the front leg, some dogs may have trouble walking (particularly up and down steps) for up to 2 weeks after surgery, and many will have swelling along the incision line for several days after the surgery.
After the surgery, the animal will stay in the hospital until the chest tube is removed, it is breathing well, and its pain can be managed with oral medications. Exercise is restricted for 10-14 days to allow the surgery site to strengthen. Some dogs may wear a bandage for 1-2 weeks after the surgery, or they may need to have their toenails cut short, to stop them from scratching at the site as it heals. Depending on the type of tumor, which is based on microscopic examination of the removed tissue, chemotherapy may be recommended. Also, veterinarians may suggest x-raying the chest twice a year to check for spread or recurrence of the tumor.
Prevention and Prognosis
Since breathing second hand smoke can increase the risk of lung tumors, the best prevention available is for the owners to stop smoking (even when owners smoke outside, the smoke is brought in on their hair and clothing).
Survival after lung lobectomy for a primary lung lobe tumor averages one year. Survival is longer when the tumor is smaller or peripheral (15-17.5 months), when the lymph nodes are small (20 months), and when the tumor can be entirely removed. Survival also depends on the tumor type and is longer in dogs with adenocarcinomas that are completely removed (19 months) than dogs with squamous cell carcinomas (8 months). The best prognosis is in animals that have small diameter, well differentiated papillary carcinomas that are diagnosed as incidental findings (before clinical signs occur) and that have no evidence of lymph node spread. Cats are much more likely to have spread of their primary lung tumors, so their prognosis may not be as good as dogs.
— Dr. Karen Tobias, DVM, MS
Reviewed 9/15/2009 by Mitchell A. Robbins, DVM, Diplomate ACVS