Retrospective histopathology audit of thymectomy specimens: A clinicopathological study of 303 cases spanning the non-neoplastic, benign and malignant spectrum

Aims: Thymectomy specimens are uncommon in routine histopathology practice. However, awareness of various pathologic entities and definite reporting of these specimens is paramount to optimal patient management. Our objective was to determine the histomorphologic spectrum of thymectomy specimens spanning the non-neoplastic, benign to malignant spectrum. Methods and Results: Thymectomies received over an 8-year period were retrospectively analyzed by reviewing clinical details and histologic findings in detail, incorporating the latest World Health Organization (WHO) 2015 histologic classification. A total of 303 thymectomy specimens (179 males/124 females, mean age 45.3 years [3–84 years]) were included. Around 51.2% (n = 155) patients had associated myasthenia gravis (MG), while 17.5% (n = 53) had incidentally detected anterior mediastinal mass (AMM). Non-neoplastic and benign pathologies comprised 31% (n = 94) cases and showed stronger association with MG (P = 0.009). Thymic follicular hyperplasia (TFH) was the commonest non-neoplastic pathology (n = 32), while the benign tumor group included thymic hemangioma/lymphangioma, thymolipoma, and ectopic parathyroid adenoma. Thymic epithelial tumors (TETs) comprised 64.7% cases, with majority being thymomas (185/303; 61.1%). Thymoma type B2 was the commonest histologic subtype and Stage I/T1 was the most frequent stage. Type A and AB thymomas affected older patients (P = 0.005) and were in lower stage (both Masaoka and American Joint Committee on Cancer [AJCC]) than type B thymomas (P = 0.007). No significant association between MG and thymoma subtype, patient sex or Masaoka stage was seen (P > 0.05). Thymic carcinomas comprised 11 cases and showed no association with MG (0/11, P < 0.001); squamous cell carcinoma was the commonest histologic type (8/11; 72.7%). Conclusion: TETs are the commonest thymic lesions; however, a diverse spectrum of pathologic processes can affect the thymus.