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The thymus is a gland located within the chest cavity, and sits in front of the heart. In the young dog, the thymus produces T-cells, which form part of the body's immune defences against infection. As the dog matures, the thymus is no longer needed to actively produce cells and shrinks down. However, in rare cases, the thymus may become cancerous in later life.
Thymectomy is the surgical procedure to remove a diseased thymus. This is a specialist procedure performed in a referral setting. The surgery commonly involves open chest surgery, gaining access either with an intercostal thoracotomy (entry between two ribs) or median thoracotomy (splitting the sternum or breastbone.)
For dogs with benign cancer of the thymus, surgical removal leads to an excellent prognosis. However, malignant tumors can be difficult to resect and do less well.
The patient is carefully assessed with preoperative MRI or CT scans. This allows the surgeon to visualize the boundaries of the thymus and aid surgical planning.
The dog is given a general anesthetic and the fur over the chest clipped. Once aseptically prepared for surgery, the surgeon performs a thoracotomy. This means gaining access to the chest cavity by making an incision between two ribs or by splitting the sternum.
Once in the chest, the surgeon identifies the thymus, ligates the blood vessels supplying it, and removes the gland. A chest drain is put in place, and the thoracotomy closed. Air is drained from the pleural space via the chest drain, the patient woken, and sent to intensive care for close observation on recovery.
Non-invasive thymic tumors are localized within the chest and can often be removed in their entirety. Many dogs then go on to recover and lead normal lives, dying at a later date from unconnected causes. The survival rates after one year are 83%, a high figure indeed.
Unfortunately, around 50% of thymic tumors are more aggressive and invade into other soft tissue structures within the chest. This includes growing around major blood vessels such as the vena cava, which makes full removal impossible. These dogs then need radiation therapy to shrink the size and reduce its impact within the chest.
Patients receiving radiotherapy for an invasive (malignant) thymic cancer have an average survival time of 200 to 300 days. There have been no scientific studies into the efficacy of chemotherapy against thymic cancer, but in some cases it anecdotally seems to be of some benefit.
Chest surgery is a major procedure and not without complications. In the immediate postoperative period, the dog is closely monitored for signs of pneumothorax (air leakage into the chest), hemorrhage, hypothermia, and infection. The chest drain is often left in place for five days, to cover the period when air leakage is most likely.
The skin sutures are removed after 10 to 14 days. The patient must avoid over exertion for several weeks after this major surgery, in order to allow full healing of the thoracotomy to take place.
There are considerable preoperative costs involved with the initial diagnosis. This includes at least $200 for a specialist consultation, and a scan at anywhere between $800 and $1,500. The cost of the procedure itself is liable to be $3,000 upwards, plus the cost of intensive care nursing at around $600 per night.
Thymectomy is a procedure with a 'black and white' outcome. For the best case scenario (removing a non-invasive tumor) the surgery can be curative, however, this is not the case for more aggressive forms of the disease where the outlook is bleaker.
Thymectomy requires a thoracotomy in order to gain access to the gland. This is major surgery and not without potential complications such as hemorrhage or infection. These risks can be minimized by carefully screening the patient for their suitability and likelihood of a good outcome, before surgery takes place.
Thymic tumors have no known cause, but tend to occur in older dogs belonging to medium or large sized breeds. Therefore it is not appropriate to think in terms of preventing this condition. However, dogs with thymic disease tend to present with nonspecific symptoms, often relating to breathing difficulties, thirst, or lack of energy. Identifying the root cause of these symptoms (i.e., a thymic tumor) early in the disease's progression helps to maximize the chance of a successful outcome to thymectomy surgery.
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