Thymic Amyloidosis Mimicking Thymoma: A Case Report

The most common anterior mediastinal tumors are thymic epithelial tumors, including thymoma, and other kinds of diseases are relatively rare. Here, we report our experience in treating a patient with amyloidosis of the thymus, a very rare type of mediastinal lesion.

We experienced thymic amyloidosis mimicking a thymoma. A 66-year-old male underwent thymectomy for an anterior mediastinal tumor, which was incidentally pointed out with chest CT. The pathological examination revealed that eosinophilic unstructured substances were present around the atrophied thymic tissue, suggesting the presence of amyloid deposits. Thus, the postoperative pathological diagnosis was thymic amyloidosis. Thymic amyloidosis is extremely rare. Since other amyloid deposits were identified in the gastric mucosa of this patient, he was diagnosed with systemic amyloidosis, and chemotherapy was initiated. The patient had no progression of amyloidosis for 21 months after surgery.

To the best of our knowledge, only 8 cases of thymic amyloidosis, including the present case, have been reviewed in the literature. Although thymic amyloidosis is extremely rare, an unfavorable prognosis has occasionally been reported. In addition, thymoma and thymic amyloidosis have similar imaging findings, thus making it difficult to distinguish between them. Therefore, thoracic surgeons may need to be aware that thymic amyloidosis is included in the list of anterior mediastinal lesions.