Background: While calcification of thymoma is common, "eggshell" calcification is rare. We report a case of an eggshell calcified thymoma that "hatched" after 4 years of follow-up. Pathologically, it revealed that sarcoidosis accompanied this case of thymoma, which might cause in calcification.
Case presentation: The patient was a 68-year-old female. A 20-mm anterior mediastinal nodule completely covered with calcification was noted in an annual health check-up. However, as the nodule did not change during 6 months of follow-up, she discontinued regular examinations. Four years later, an abnormality in her chest X-ray was noted again. The tumor grew outside the calcification to reach 63 mm. She underwent resection of this anterior mediastinal tumor. Pathologically, the tumor was diagnosed as thymoma of type B1 in the WHO classification. The histology of the tumor inside and outside of the calcification was not different, suggesting that the tumor grew from the inside of the calcification. The calcification was located within the fibrotic capsule of thymoma. Sarcoidosis also presented in her lung and mediastinal lymph nodes.
Conclusions: Although the mechanism of calcification of the capsule was not clear, sarcoidosis might be related to this case because macrophage accumulation and altered lipid metabolism in sarcoidosis present with similar dystrophic calcification.
Keywords: Eggshell calcification; Rim calcification; Round-shaped calcification; Sarcoidosis; Thymoma.