Thymoma Case Report: Entire-Tumor Calcification
Background
Thymoma is a type of anterior mediastinal tumor that is quite common. It represents around 50% of anterior mediastinal masses and around 20-30% of all types of mediastinal tumors. Thymomas are hard to distinguish between invasive or encapsulated types. Thymomas often affects patients in their middle ages. Most cases also happen to people around 55 to 65 years of age. The frequency also increases as age increases. From 3% at age of 29, incidence reaches 12% for ages 21 to 45 years, and 35% over 46 years old.
Thymomas are often found in the anterior mediastinum, but they can also grow in other places such as the heart, lungs, trachea, neck, and thyroid. Thymomas are also associated with syndromes such as pure red cell aplasia, myasthenia gravis, and other kinds of immune-mediated systemic disorders. Thymomas are tumors of the thymic epithelial cells and they are often differentiated through their inconsistent biologics behavior. Calcification of thymoma occurs, but only on rare occasions does it cover the entire thymoma. Most calcifications in thymomas are amorphous and positioned deep within the lesion. They are easily detected through radiology.
The frequency of calcification ranges from 10% to 40% for type B thymomas. Calcification of thymomas is also associated with lipid metabolism, abnormal disposition of calcium salts, and degenerative tissue. Ossification is related to abnormal endocrine status and growth factor issues. The rarest type of thymomas are ones with ring calcifications.
Calcification often occurs seven to eight months after treatment. The calcification rate ranges from 0% to 26% for noninvasive thymomas and around 17% to 54% for invasive thymomas. Most thymomas are classified into different stages, which determine the type of management and treatment for these tumors. The known calcification shape patterns in thymoma are nodular, ringed, and stippled. Also, a majority of thymomas are low-grade malignant neoplasms.
Epidemiology
Thymoma is a relatively rare neoplasm that accounts for around 0.2 – 1.5% of all malignant neoplasms. Most thymomas have small nodular calcifications. An entire-tumor calcification has never been reported, which makes this case rare. In this case, the patient had a thymoma which was completely occupied by calcification. Thymomas have two basic cell types: spindle or oval and round or epithelioid. Type A thymoma is oval cells with scattered nuclear chromatin and absent nucleoli without mitotic activity. Type Ab thymomas are identical to type A but are mixed with small lymphocytes. Tye B1 are round cells with small eosinophilic nucleoli and abundant cytoplasm. They are also often mixed with small T-lymphocytes. Type B2 is an equal mix of round and small lymphocytes. Type B3 has large round cells with scant lymphocytes. The potential of a thymoma to become malignant is often determined by its invasiveness. Therefore, thymomas that have no local invasion are considered benign tumors.
The Thymus Gland
The thymus gland is found in the anterior mediastinal compartment of the chest. It originates from the fourth and third branchial pouches. It also includes three germinal layers. During the pre-adolescent period, the thymus gland is most active and largest in size. As the thymus gland changes with age, imaging for medical purposes must also change. During puberty, the thymus attenuation on the CT scan is often proportionate to the adjacent musculature.
Radiologic Features
The radiologic appearance of thymoma is shown by a contour abnormality of the mediastinum. Most radiographic abnormalities also range from small, subtle, or abnormal mediastinal opacities to large anterior mediastinal masses. If there is no local invasion, the masses show the parietal and visceral pleural surfaces. You can also see the smooth marginated lobulated borders against the adjacent lung. Most thymomas are unilateral masses that protrude into one hemithorax. They also extend to both sides of the midline. They may also conform to the adjacent cardiac border.
Clinical Case
A 49-year-old woman was admitted to the hospital with the chief complaint of a productive cough. Her chest X-ray showed an abnormal darkening or shadow. She had no past medical history of note and her blood examinations were normal. However, she recently had pneumothorax surgery. Tomography showed an anterior mediastinal 40-mm mass with massive calcification. Magnetic resonance imaging showed T1-weighted and T2-weighted heterogeneous signal intensities. Preoperative differential diagnoses were calcified lymph node, hemangioma, hamartoma, teratoma, or thymic tumor with calcification. Hematoxylin and eosin staining revealed calcification with oval and round cells and lymphocytes.
Through the use of video-assisted thoracoscopic surgery, the patient underwent a mediastinal tumor excision process. The tumor was of 40 x 40 mm in size. Almost all parts of it showed ossification and calcification. Findings revealed that the patient had a type B3 thymoma with massive calcification covering almost all of the thymoma. Because of the high risk of recurrence, the surgeons performed full thymectomy. Results showed that no remaining thymoma tissue was found in the residual thymus. There was also no evidence of recurrence 2 years after the first surgery.
Treatment
Surgical resection is the gold standard of treatment for patients with thymoma. Stage I thymoma is treated with surgical resection. Stage II is treated with extended thymectomy. Stage III is complete resection. Patients in stage 3 also receive neoadjuvant chemotherapy for more effective resection. Stage IV thymomas is treated with chemotherapy with palliative intent.
Conclusion
Most thymomas today are diagnosed through computed tomography. When there are symptoms, they are often found in local regions where the tumor has spread. It can manifest into dysphagia, superior vena cava syndrome, and diaphragm paralysis. There are numerous studies that reported the occurrence of calcified thymomas, However, thymomas with full calcification are relatively rare. Only a few cases are ever reported in the literature. It’s possible that the patient’s previous pneumothorax surgery may have caused local inflammation which caused the calcification of her tumor.
Most imaging findings are also unable to predict the right stage and prognosis for thymoma patients with this condition. Surgery is the mode of treatment for all thymomas except for stage 1 tumors which can benefit from adjuvant radiant therapy. Local invasion and spread of tumors is the most important factor for survival. The leading cause of death for invasive thymomas is cardiorespiratory complications including cardiac tamponade.
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