Mediastinal Tumors: Thymoma and Thymectomy
The thymus gland is located in the anterior mediastinum, between the two lungs, in front of the heart and behind the sternum.
It is an organ of the immune system whose function reaches full maturity during adolescence, while later during early adulthood it regresses and is gradually replaced by adipose tissue.
Thymomas are tumors of the thymus gland, generally developing slowly, and while it was previously believed that there were benign and malignant forms, all thymomas are now considered potentially malignant tumors, that is, depending on their type, they have the ability to grow, invade neighboring organs and spread locally or even distantly. Their etiology remains unknown, while they may be associated with the presence of various syndromes, the most common of which is myasthenia gravis.
About one-third of patients with thymoma are asymptomatic, and thymoma is diagnosed incidentally as an anterior mediastinal mass on a chest CT or MRI scan performed for another reason. Another third of patients present with vague and mild chest symptoms, which are usually present for a long time.
These symptoms are nonspecific and may include cough, a feeling of heaviness or pressure in the chest, and mild dyspnea.
Finally, one-third of patients with thymoma present with some manifestation of myasthenia gravis. Precisely because of the frequent coexistence of thymoma and myasthenia, if myasthenia has not been previously diagnosed, testing for acetylcholine receptor antibodies is recommended, especially in younger patients diagnosed with thymoma.
Thymomas should be surgically excised when they are in early stages and the resection should preferably include the entire thymus gland.
Quite often, and when the clinical diagnosis of thymoma by CT or MRI is very likely and early stage, preoperative biopsy is not necessary and the patient can proceed directly to surgical excision, which, in most cases, is now performed with minimally invasive techniques.
While thymomas are predominantly well-circumscribed solitary tumors, resection of all tissue from the anterior mediastinum is important oncologically, in order to remove all sites where ectopic thymic tissue may be present and which may lead to local recurrence.
For more advanced cases, induction chemotherapy is recommended and then the possibility of complete surgical resection is assessed, followed by postoperative radiotherapy.
Furthermore, when thymoma coexists with myasthenia gravis, surgical resection should be performed when the symptoms of myasthenia have been controlled as much as possible and the immunosuppressive medication that the patient receives is as minimal as possible.
In contrast to thymic tumors, thymic hyperplasia is a benign condition in which hypertrophy of the thymus gland is observed. Surgical resection is recommended for rare cases that cause local pressure phenomena or when it is combined with myasthenia gravis or other rarer autoimmune diseases and thymectomy is deemed necessary.
