What are Tumor of the Thymus?
Thymoma is a rare tumor that most commonly affects medium to large breed dogs and is most often found in the Labrador and German Shepherd breeds. Most thymomas occur in older dogs, with the median age of 11 years. Thymomas may cause cranial caval syndrome, hypercalcemia, aspirational pneumonia, and/or myasthenia gravis.The thymus is an organ within the lymphatic system located inside the chest cavity just in front of the heart. The thymus produces a subset of lymphocytes, or white blood cells, called T-cells, which are integral in killing foreign cells, activating other immune cells to fight infection, and ceasing the immune response once a threat has been eliminated. A thymoma is a rare tumor originating from the epithelium of the thymus, or the layer of tissue surrounding the thymus.
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Symptoms of Tumor of the Thymus in Dogs
- Labored breathing
- Rapid breathing
- Cranial caval syndrome: swelling of the head, neck, and forelimbs, fluid build-up in the chest
- Myasthenia gravis: muscle weakness, enlarged esophagus, frequent regurgitation
- Hypercalcemia (high calcium level in the blood): increased thirst, increased urination, decreased appetite, weakness, and lethargy
- Decreased exercise tolerance
- Difficulty swallowing
- Weight loss
- Paralysis of voice box
- Aspirational pneumonia
- Abnormal heartbeat
TypesThymomas can be invasive or non-invasive, with each type occurring at about a 50% rate. Even more rare is a thymic carcinoma, a malignant tumor that metastasizes to other parts of the body.
Causes of Tumor of the Thymus in Dogs
The cause of thymoma is completely unknown.
Diagnosis of Tumor of the Thymus in Dogs
The veterinarian who you've brought your dog to will conduct a thorough physical examination of your dog and ask you to recount the onset of symptoms in order to aid diagnosis. A chemical blood profile to measure levels of proteins and calcium in the blood will reveal hypercalcemia, which affects 5% of dogs with thymoma. A complete blood count will measure red and white blood cell and platelet levels in order to detect any abnormalities and anemia, which can be found in some dogs with thymomas. Your dog’s blood will also be tested for the presence of antibodies to acetylcholine receptors, which would be a positive indicator of myasthenia gravis. Another indicator of myasthenia gravis is a Tensilon test, which for which your dog will be injected with tensilon (also called edrophonium) and his muscle movements will be tested. If your dog has myasthenia gravis, muscle strength will be improved during the test. Further, a urinalysis will measure mineral content, glucose and protein levels in your dog’s urine.
X-rays are an important diagnostic tool, and will indicate a build-up of fluid in the lungs, as well as the presence of a mass which may be in between the functioning lungs, on the thymus or in front of the heart, and the presence of an enlarged esophagus, which is a symptom of myasthenia gravis. Definitive diagnosis depends upon a biopsy of the mass, which is most commonly conducted once the mass has been entirely surgically removed and is most likely the case with thymoma. If other tumors are present, they will more likely be diagnosed through a fine-needle aspiration biopsy prior to surgery. CT scans, MRIs or chest ultrasounds may be conducted.
Treatment of Tumor of the Thymus in Dogs
Surgery is the primary treatment for thymoma. Tumors may be removed through open surgery, during which the ribs are spread, or the breastbone is cut with a saw. However, some veterinary surgeons may offer a procedure known as VATS, or video-assisted thoracoscopic surgery, in which a camera on a thin tube, or thoracoscope, is inserted into the chest through a small incision and instruments that can remove the tumor are inserted into the chest cavity through two other small incisions. VATS is less invasive and can reduce in-hospital recovery time; however, it may not be available in your area.
Another treatment option only recommended in cases where the tumor cannot be removed surgically, is radiation, which is effective in 75% of cases. Radiation side effects include inflammation of the heart sac and lungs. Radiation treatments are administered daily for a period of 18 to 21 treatments. Chemotherapy is found to be ineffective and is not considered a viable treatment option for thymoma.
Recovery of Tumor of the Thymus in Dogs
The prognosis for invasive thymoma is guarded, as is that of dogs receiving radiation therapy. Dogs receiving radiation therapy have a median survival time of 248 days following treatment. The prognosis for thymic carcinoma is very poor. Prognosis is also negatively affected by concurrent myasthenia gravis and aspiration pneumonia.
The prognosis for noninvasive thymoma is excellent, particularly in dogs whose thymoma is completely removed.
Regardless of the method of treatment, follow-up appointments will be scheduled in order to review x-rays and monitor the tumor’s size, and/or recurrence you're your dog does undergo surgery, management of surgical sites is incredibly important, as is easing your dog into home life after surgery. Be sure to follow all post-surgery instructions, paying special attention to guidance on diet, pain management, and activity.
Tumor of the Thymus Questions and Advice from Veterinary Professionals
Today I finally got an answer about my 7yr old pit bull. After 3 months of not knowing I got blood work done but nothing came of it. And a pancreas test was negative. I got two separate sets of X-rays done. Dr says there is a mass effect in the cranial thorax. And they think it's cancerous. But it's out of their reach. What's the best way to go about dealing with this? I have no experience?
Masses in the thorax can be difficult to diagnose, manage and treat; usually surgical excision is the treatment of choice but is a costly procedure that carries a level of risk (due to opening the rib cage and requiring artificial ventilation); additionally, the invasiveness of the mass will determine if it can be removed fully. An ultrasound would be useful to get a better idea of the invasiveness and blood supply of the mass; a biopsy may also be taken during this time (guided by the ultrasound) to help to determine if the mass is malignant or not. The origin of the mass, location, invasiveness and type of cells would determine treatment and prognosis. Regards Dr Callum Turner DVM
Extremely thank you so much. I appreciate the clear and concise answer of going about dealing with Roscoe. Thank you again.
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I would like to know how quickly a thymoma grows in size.
My sweet boy died during surgery to remove a non-invasive thymoma. Because of all of the tests that were done, & having to wait to receive the reports on them, it took 1 month from discovery of the tumor to surgery being done. His symptoms became more distressing as time passed.
He was supposed to have been given an IV med for Hypercalcemia last week in preparation for surgery this Monday 10-17 but his calcium levels were normal so he didn't get it. When prepping for surgery 10-17 his calcium levels were high again so he got IV med & surgery was delayed until 10-19.
On 10-19 calcium levels were good so proceeded with surgery. An hour & a half in to the surgery his heart stopped. The surgeon wasn't able to resuscitate him. The surgeon said that Beau hadn't been getting much oxygen for the last few days. The tumor had totally compressed 1 lung & partially compressed the other. It was also pressing against his heart. When I asked how large the tumor was he said it was the size of a watermelon. It basically filled most of his chest.
I had been asking how large it was & was always told it was good sized. Shouldn't they have been able to tell how large it was from his xrays, CT &/or ultrasound?
Thank you in advance for your help. I'd really appreciate any information about the growth rate, especially in relation to size increase, for this type of tumor.
Sorry about your loss, it is normal to ask questions after the death of a loved one especially if the death occurred during surgery. Thymoma’s are generally considered to be slow growing tumours but highly invasive, but may grow to a size where the heart and lungs are displaced and fills the majority of the thoracic (chest) cavity; the level of displacement of the thoracic organs can be visualised easily on a simple x-ray of the chest. The Thymoma can get quite large and an animal is still able to breathe (with difficulty). I am unable to comment on what size the tumour was before surgery, what your Veterinarian determined to be ‘good sized’ or the rate of growth (which is considered slow for Thymoma’s); Thymoma’s can cause secondary conditions including Myasthenia Gravis, Megaesophagus (enlargement of the oesophagus), inflammation of muscles, Hypercalcemia (which Beau had) and other tumours. Surgery is always a risky business, even in young healthy animals there is always a risk of complications (very rare) with anaesthetic agents. Regards Dr Callum Turner DVM
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One of my dogs died in the age of 10 months without any signs to be sick. He was active, had good apetite.
After the autopsy my vet told that the dog had problem with thymus. I would like to know if problems with the thymus could cause death in such an early age?
Condolences on your loss. The thymus is a gland which functions as part of the immune system and is located in front of the heart. Hematoma (accumulation of blood) of the thymus can cause sudden death in dogs; the hematoma is usually caused by trauma from car accidents or severe trauma including excessive stretching of the neck by different means, there are reports of spontaneous bleeding into the thymus gland without a traumatic cause. Other conditions (i.e: tumours of the thymus gland) would show symptoms of respiratory distress, increased drinking and urination, difficulty swallowing and irregular heartbeat before leading to death. Regards Dr Callum Turner DVM
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My dog is 13 years old and has Thymoma. The tumor is about 2.5 inches and symptoms are not yet present. Is it recommended to operate on a dog this old?
Surgery always carries risk, even in a healthy animal; as dogs get older their tolerance for the anaesthetic and the trauma of the surgery decrease. Usually when surgery is being considered in an older dog, a blood count and biochemistry test is carried out to assess the internal health of the dog, especially their liver and kidney’s. The surgery on the Thymus gland is invasive and requires opening the thorax (chest) cavity. Other options apart from surgery is radiation therapy, I would ask your Veterinarian if they believed Sampson would be suitable for radiotherapy. Regards Dr Callum Turner DVM
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