Thymomas and mediastinal tumors

A thymoma is a tumor of the anterior mediastinum arising from the epithelial cells of the thymus gland (Fig. 1). Its prevalence is 0.13 per 100,000 people and despite its relatively uncommon occurrence, it still accounts for half of all tumors of the anterior mediastinum. Although it affects all age groups, it is seen most frequently in people between 50 and 60. In thisgroup of age, a thymoma is frequently associated with a neuromuscular weakness, known as myasthenia gravis. Both sexes are equally affected. About 30% of all patients with a thymoma are asymptomatic, meaning that the tumor is discovered by chance during a radiological examination. Among symptomatic patients, 40% complain of pressure or pain and coughing or shortness of breath.

 

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Fig. 1: The thymoma originates in the thymus and is typically found in the anterior mediastinum (red).

The thymoma, including its extent, is best detected and diagnosed through computed tomography (Fig. 2). In the case of excess tissue in the region, it is not always a thymoma, but may simply be a non-specific enlargement of the thymus gland. On a CT scan, a thymoma appears as a homogeneous tumor with well-defined boundaries to the surrounding tissue; e.g. smooth borders with lobulations.

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Fig. 2: Computed tomography of a patient with a type A thymoma with lobulated boundary (arrows).

The thymoma may be discovered in various stages (stage I-IV, World Health Organization (WHO)). Classification into a particular stage depends on several variables, but above all growth into adjacent or distant organs or lymph nodes. These criteria have been adopted internationally and serve as generally accepted guidelines. Treatment is selected on the basis of these criteria.

If a thymoma can be easily removed surgically, based on the available imaging, no biopsy is required beforehand. Primary surgical removal is therefore the preferred treatment and entails removing the entire thymus, including the surrounding fatty tissue. Until a decade ago, the safe removal of the tumor required opening the sternum. Today, however, minimally invasive keyhole thoracoscopic) surgery is available for a less traumatic and safer removal of the thymoma. It can be performed either with video-assisted thoracoscopy or with the assistance of robotics at specialist centers. However, this applies only to early tumor stages; removal in advanced stages requires open surgery. The main objective of any operation is the complete removal of all tumor tissue. If removed entirely in early stages of the thymoma, the short and long-term prognosis is very good. However, the prognosis depends on the particular stage; i.e. primarily, the size and extent of the thymoma.

If it is an advanced stage thymoma, accompanying (adjuvant) treatment (chemotherapy) may be required either before or after surgery. In general, chemotherapy is recommended when the tumor has spread to adjacent or distant tissue. Radiotherapy, however, is controversial at all stages of the thymoma and is generally not recommended as an adjuvant therapy.

In any case, all patients with a thymoma will be discussed in an interdisciplinary tumor conference of specialists in tumor medicine, thoracic surgery, radiology, radio-oncology and pathology, and recommendations will be made on the basis of current international findings, evidenceand standards.

After successful treatment, a CT scan should be performed annually for the first five years after surgery and then every two years up to the 10th year for the detection of any recurrence. In case of recurrence, surgery should be performed, as this treatment offers the most favorable prognosis.