Micronodular Thymoma with Lymphoid Stroma: A Case Report.

BACKGROUND Micronodular thymoma with lymphoid stroma (MNT) is a rare subtype of thymic neoplasms. Therefore, clinical guidelines, histopathological diagnostic criteria, prognostic factors, and therapeutic regimens have not been established. CASE PRESENTATION A 69-year-old woman was admitted to our hospital because of an abnormal shadow detected by chest radiography. Further imaging revealed an anterior mediastinal tumor measuring 65×28×15 mm. We performed thymectomy for diagnosis and treatment. Histopathological examination revealed spindle cells comprised multiple micronodules separated by abundant interstitial lymphocytes and lymphoid follicles. Immunohistochemical staining showed that the tumor was positive for cell adhesion molecule (CAM), cytokeratin (CK) 5/6, and terminal deoxynucleotidyl transferase. The histopathological diagnosis was MNT and the stage was I by the World Health Organization classification. The patient remained free of recurrence for seven years after surgery. CONCLUSION When the lesion is completely resected, MNT has a good prognosis. Therefore, MNT is considered to be a borderline tumor with good prognosis and no reports of recurrences, distant metastasis, or tumor-related deaths exist thus far. However, preoperative diagnosis is difficult in most cases. Hence, complete surgical resection is recommended for suspicious mediastinal masses, if feasible, for both accurate diagnosis and to ensure long-term survival.