A closer look: Tumor of the Thymus in Dogs
The thymus is an organ located in the chest cavity in front of the heart. It acts as a part of the immune system to produce mature T cells used to fight disease in the body. Thymomas are often associated with myasthenia gravis.
Thymoma is rare in dogs and has a good prognosis with surgical removal. Secondary myasthenia gravis is commonly associated with aspiration pneumonia, which is a life-threatening emergency.
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Additional conditions associated with thymic tumors include myasthenia gravis syndrome and hypercalcemia.
The cause of thymoma is unknown. It is most common in medium and large breeds, with Labrador Retrievers and German Shepherds over-represented.
Non-invasive thymic tumors are sometimes asymptomatic.
Invasive tumors of the thymus can present with the above signs, as well as cranial vena cava syndrome. The characteristic symptom of cranial vena cava syndrome is swelling of submandibular area, neck, thoracic inlet, and thoracic limbs.
Testing and diagnosis
The first steps to diagnose a case of possible thymoma are physical exam, blood work, urinalysis, and x-rays. Tumors are usually identified in x-rays, but other imaging techniques may also be recommended (ultrasound, CT, MRI). From there, ultrasound guided or surgical biopsy may be performed. Exploratory thoracotomy (exploring the upper chest area surgically) may be necessary to differentiate invasive and non-invasive tumors.
Steps to Recovery
Treatment is surgical removal of the tumor, if possible. If the tumor has invaded the vital organs of the chest and excision is not possible, radiation therapy is the treatment of choice.
In dogs with secondary myasthenia gravis, treatment also requires intensive care to ensure they are receiving adequate nutrition, medical intervention with immunosuppressants, anticholinesterase medications, motility drugs, histamine antagonists, and antibiotics for management of megaesophagus.
Prognosis with complete surgical removal is excellent and usually curative. In about 1/3 of cases, the tumor recurs locally, and a second surgery is likely to be effective. In cases where the tumor has metastasized (rare), cannot be removed, and/or is associated with aspiration pneumonia, prognosis is guarded to poor.
As the cause is not known, specific prevention is not identified. Thymoma is not contagious. Regular veterinary care can help detect symptoms early.
Is Tumor of the Thymus in Dogs common?
Thymoma is rare in dogs.
- Surgical removal of tumor
- Radiation therapy
- Medical management of associated syndromes (immunosuppressants, anticholinesterase medications, motility drugs, histamine antagonists, and antibiotics)