Dogs have 13 pairs of ribs that form the supportive structure (rib cage) of the chest cavity. The ribs attach onto the breastbone and the backbones. The vital structures such as the heart and the lungs are protected by the rib cage. The muscles of the chest pull on the ribs during inspiration to increase the size of the chest cavity to pull air into the lungs. As the muscles relax, the rib chest cavity size gets smaller, and air is breathed out.
Types of rib tumors
The most common type of rib tumor is osteosarcoma. This is a malignant tumor with a rapid spread rate (metastasis). The second most common tumor is chondrosarcoma. This tumor has a much lower metastatic potential. Other common tumors that affect the ribs include fibrosarcoma and hemangiosarcoma.
Breeds that most commonly develop rib tumors include golden retrievers, mixed breeds, Labrador retrievers, bassett hounds, dobermans, Australian shepherds, British bulldog, German short-haired pointer, rough coated collie, Irish setter, giant Pyrenees, Rottweiler, giant schnauzer, shar-pei and springer spaniel. Two age groups of dogs tend to develop this type of tumor, young dogs (2 to 4.5 years) or middle-aged (7 to 9 years).
The most common sign of a rib tumor is a mass that is visibly or palpably present. Lameness of the forelimb may be present if the tumor 1) is located within one of the first four ribs, 2) is compressing the nerves to the limb, 3) is causing mechanical interference with movement of the limb, or 4) is invading the muscles of the forelimb. Labored breathing may be noted if the tumor is very large and is causing collapse of the lung. If the tumor has metastasized to the inside of the chest cavity, fluid may build up in the chest, compress the lungs and cause labored breathing.
The diagnosis of a rib tumor is commonly made on X-rays. Typically, the tumor will cause a portion of the rib bone to be dissolved away and/or new bone to be produced within the region of the tumor. Chest X-rays are also used to identify visible spread of the cancer to the lungs; it is important to note that microscopic spread of tumor to the lungs cannot be detected with X-rays. A CT scan may be recommended, as this test provides a better evaluation of the extent of the disease and is more sensitive to detect evidence of metastasis into the lungs. A fine needle biopsy may be helpful to diagnose a rib tumor, but frequently will not ascertain the specific type of tumor. Usually the entire tumor is submitted for biopsy after surgery is performed to establish a final diagnosis. If available, a whole body nuclear bone scan is recommended prior to surgery, as roughly 16% of the rib osteosarcomas will have spread to other bones at the time of diagnosis. In preparation for surgery, preoperative blood work including a complete blood count, chemistry profile and urine testing are recommended to ensure that your pet is healthy enough to undergo anesthesia and surgery.
Surgery is the recommended treatment option for rib tumors. In addition to the rib(s) that are affected by the tumor, one unaffected rib in front and behind the tumor should be removed. If the tumor is adherent or invading into a lung lobe or the sac surrounding the heart, this tissue will also be removed. In dogs, this is generally tolerated very well. In some cases, a plastic mesh patch will be used to repair the defect in the rib cage. In most cases, a muscle (latissimus dorsi or external abdominal oblique muscle) will be used to repair the defect in the rib cage. A drainage tube is placed within the chest cavity, and another drainage tube may be placed beneath the skin and muscle flap.
Expected local recurrence is seen in 25% of dogs with incompletely removed tumors and 13.3% of dogs with completely removed tumors. Dogs with osteosarcoma that have elevation of the alkaline phosphatase enzyme level on chemistry profile have a much lower median survival time (210 days versus 675 days). Chemotherapy will significantly increase the survival of dogs with rib osteosarcoma from a few months to about 9.5 months. Chondrosarcomas have a very good chance to be cured with surgery alone with median survival times exceeding three years. Elevation of the alkaline phosphatase enzyme level may also be seen in patients with chondrosarcomas, but this does not worsen the prognosis in these cases. These tumors can spread and cause death. The grade of a chondrosarcoma generally does not correlate with the malignant potential, and chemotherapy likely is of little benefit. Hemangiosarcoma generally carries a very poor prognosis regardless of treatment.
For more information on this subject, speak to the veterinarian who is treating your pet.