Micronodular thymoma with lymphoid stroma diagnosed 10 years after the first operation: a case report

INTRODUCTION: Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma. Here we report a case of micronodular thymoma with lymphoid stroma that was completely resected after incomplete resection 10 years earlier. CASE PRESENTATION: A 70-year-old Japanese woman who had undergone resection for a thymic cyst 10 years earlier was found to have a solid nodule with a multilocular lesion at the site of the previous operation. We suspected that the tumor was a malignant tumor and performed trans-sternal radical thymectomy and diagnosed the lesion as micronodular thymoma with lymphoid stroma pathologically. When we reassessed the thymic cyst that had been resected 10 years earlier, a few lesions of micronodular thymoma with lymphoid stroma were found in the cyst wall. Based on these findings, we concluded that only the cystic component of micronodular thymoma with lymphoid stroma had been removed, and that the residual lesion grew locally over the next 10 years before being completely resected by reoperation. CONCLUSION: We experienced an unusual case of micronodular thymoma with lymphoid stroma, which is a rare subtype of thymoma. Greater care should be taken to exclude a thymoma with a cystic lesion, even if a thymic cyst is strongly suspected on computed tomography and magnetic resonance imaging.