Thymic cancers are exceedingly rare, with an incidence of one to two cases per 100,000 person-years, with exceptionally diverse presentations. True incidence is unknown.
With increasing use of CT of chest for lung cancer screening, cardiac screening and preoperative evaluations, we have experienced an increase in diagnosis of thymic tumours. Thymic epithelial tumours make up 35% of all anterior mediastinal mass while lymphoma and germ cell tumours make up the other most common pathologies.
About a third of the patients with thymoma can be associated with myasthenia gravis. One of the biggest challenges of incidentally diagnosed thymic mass is its management.
The following tests are most useful in making diagnosis of thymic tumours in descending order:
- CT chest with contrast
- MRI of chest
- PET scan
- Biopsy
Radiology is the mainstay of the diagnosis of thymic tumours. CT scan is most commonly used radiological test followed by MRI. Contrast CT scan is highly desirable to assess the relationship of thymic tumour with great vessels, pericardium, phrenic nerves and heart. CT scan is quite reliable in making diagnosis of thymoma with high probability, based on tissue characteristics, location, shape and invasion.
MRI is used to distinguish solid thymic tumour from thymic cyst which are likely benign. Other use of MRI is to assess invasion of mediastinal structure by thymic tumour in particular thymic carcinoma.
Pre-treatment biopsy for diagnosis is not always necessary as long as robust diagnosis of thymic tumour can be made with radiology and the tumour is surgically resectable. Biopsy is considered under following circumstances:
- High probability of other diagnosis e.g. lymphoma or germ cell tumours
- Patient prefers for surveillance rather than excision – biopsy to rule out cancer.
One of the side effects of large biopsy is breaching of capsule, in case of thymoma. Thymoma are notorious for causing drop metastasis if the spillage occurs after biopsy.
The surgical approaches for thymectomy are sternotomy, video-assisted thoracoscopic surgery or robotic thymectomy.
Sternotomy has been a standard approach for many years for most surgeons. It provides great exposure and allows for simple as well as complex thymectomy for thymic tumours. But sternotomy approach is also associated with morbidities of sternal split, bleeding, pain, infection, scarring and prolonged hospital stay and recovery.
Many of the disadvantages of sternotomy are overcome by VATS and Robotic approaches. VATS approach has been limited to those who expertise in VATS surgery. Only few surgeons carry out VATS thymectomy routinely in Australia. Minimally invasive approach is ideal for smaller thymic tumours (less than 5cm).
Robotic thymectomy
Robotic thoracic surgery has been available in Australia for more than a decade, but it was first introduced to Perth in July 2023.
It is a port access technology for keyhole surgery. Robotic arms are introduced in the chest cavity by multiple (usually three) ports. Robotic arms are controlled by the robotic thoracic surgeon who is not scrubbed at the operating table but is present in operating theatre working on the robotic console. Multiple studies have consistently shown that robotic thymectomy has many advantages.
One of the biggest is 3D vision allowing surgeons to visualise intrathoracic structures as the surgeon would see it in open cases. Robotic technology comes with high definition camera technology and significant magnification of structures which allows for better visualisation of anatomy with improved precision to carry out surgical steps. The surgeon has control of all the instruments rather than assistant surgeon. Surgery generally takes around 60-80 minutes and hospital stay is usually less than two days.
Key messages
- Thymoma is the commonest pathology of thymic epithelial tumours
- Contrast enhances CT scan is one of the most reliable test for diagnosis and role of biopsy is debatable
- Best treatment for thymoma is surgical excision with excellent long-term outcomes. Robotic thymectomy has advantages over VATS thymectomy and sternotomy.
Author competing interests – the author was the first in WA to introduce robotic thymectomy