BACKGROUND True thymic hyperplasia is a rare condition characterized by enlargement of the thymus while its normal structure is retained. True thymic hyperplasia is known to accompany Graves' disease, but no association between true thymic hyperplasia and thyroid follicular tumor has been reported so far. We report a case of true thymic hyperplasia in a patient with a thyroid follicular tumor. CASE PRESENTATION A 52-year-old Japanese man was referred to our hospital for evaluation of a thyroid mass and a mediastinal mass. His serum thyroglobulin level was high, and hemithyroidectomy was performed to remove the thyroid mass. The resected mass was diagnosed as a follicular tumor of uncertain malignant potential. After resection of the thyroid lesion, the patient's serum thyroglobulin levels were markedly decreased. Seven months later, the patient underwent resection of the mediastinal mass. On pathological examination, the mass was found to consist of lobules, which formed a corticomedullary structure with Hassall's bodies, indicating a normal thymic mass with hyperplastic thymic tissue, less organized cellular cords, and intermingled adipose tissue. Immunostaining for cytokeratin 19 and cytokeratin 7 indicated that the lesion was consistent with thymic tissue. The lesion was diagnosed as true thymic hyperplasia, and the histological findings suggested that secondary atrophy had occurred. No evidence of recurrence was observed at 24 months after surgery. CONCLUSIONS We present a case of a combination of true thymic hyperplasia and thyroidal follicular tumors that, to our knowledge, has not been reported previously. High serum thyroglobulin levels might play a role in hyperplasia of the thymus. Although true thymic hyperplasia is a rare disorder, it should be included in the differential diagnosis of a mediastinal mass in patients with thyroid disease.

中文翻译：

---

真正的胸腺增生与甲状腺滤泡性肿瘤之间罕见的关联：一例报告。

背景技术真正的胸腺增生是一种罕见的疾病，其特征在于胸腺增大而其正常结构得以保留。已知真正的胸腺增生会伴有Graves病，但到目前为止，尚未报道真正的胸腺增生与甲状腺滤泡性肿瘤之间的相关性。我们报告甲状腺滤泡性肿瘤患者真正的胸腺增生一例。病例介绍一名52岁的日本男子被转介到我院评估甲状腺肿块和纵隔肿块。他的血清甲状腺球蛋白水平很高，并进行了甲状腺切除术以清除甲状腺肿块。切除的肿块被诊断为恶性潜能不确定的滤泡性肿瘤。甲状腺病变切除后，患者的血清甲状腺球蛋白水平明显降低。七个月后，病人行纵隔肿块切除术。经病理检查，肿块由小叶组成，与哈索尔的身体形成了皮质髓质结构，表明正常的胸腺肿块具有增生的胸腺组织，组织较少的细胞索和混合的脂肪组织。细胞角蛋白19和细胞角蛋白7的免疫染色表明，病变与胸腺组织一致。该病变被诊断为真正的胸腺增生，组织学检查结果表明已发生继发性萎缩。术后24个月没有观察到复发的迹象。结论我们提出一例真正的胸腺增生与甲状腺滤泡性肿瘤合并的病例，据我们所知，以前没有报道。血清甲状腺球蛋白高水平可能在胸腺增生中起作用。尽管真正的胸腺增生是一种罕见的疾病，但应将其包括在甲状腺疾病患者的纵隔肿块的鉴别诊断中。