Department of Pathology, Rutgers New Jersey Medical School, Newark, New Jersey.
Department of Pathology, Medical College of Wisconsin, Milwaukee, Wisconsin.
Mod Pathol. 2023 Aug;36(8):100207. doi: 10.1016/j.modpat.2023.100207. Epub 2023 May 5.
Thymic hyperplasia is a rare condition generally caused by lymphoid follicular hyperplasia associated with autoimmune disorders. True thymic parenchymal hyperplasia unassociated with lymphoid follicular hyperplasia is extremely rare and may give rise to difficulties in diagnosis. We have studied 44 patients with true thymic hyperplasia (38 females and 6 males) aged 7 months to 64 years (mean, 36 years). Eighteen patients presented with symptoms of chest discomfort or shortness of breath; in 20 patients, the lesions were discovered incidentally. Imaging studies demonstrated enlargement of the mediastinum by a mass lesion suspicious for malignancy. All patients were treated with complete surgical excision. The tumors measured from 3.5 to 24 cm (median, 10 cm; mean, 10.46 cm). Histologic examination showed lobules of thymic tissue displaying well-developed corticomedullary architecture, with scattered Hassall corpuscles separated by mature adipose tissue and bounded by a thin fibrous capsule. No cases showed evidence of lymphoid follicular hyperplasia, cytologic atypia, or confluence of the lobules. Immunohistochemical studies showed a normal pattern of distribution for keratin-positive thymic epithelial cells against a background rich in CD3/TdT/CD1a lymphocytes. Twenty-nine cases had an initial clinical or pathological diagnosis of thymoma or thymoma vs thymic hyperplasia. Clinical follow-up in 26 cases showed that all patients were alive and well between 5 and 15 years after diagnosis (mean, 9 years). Thymic parenchymal hyperplasia causing significant enlargement of the normal thymus that is sufficient to cause symptoms or worrisome imaging findings should be considered in the differential diagnosis of anterior mediastinal masses. The criteria for distinguishing such lesions from lymphocyte-rich thymoma are presented.
胸腺增生是一种罕见的疾病，通常由与自身免疫性疾病相关的淋巴滤泡增生引起。与淋巴滤泡增生无关的真正胸腺实质增生极为罕见，可能导致诊断困难。我们研究了 44 例真正的胸腺增生患者（38 名女性和 6 名男性），年龄 7 个月至 64 岁（平均 36 岁）。18 例患者出现胸痛或呼吸急促症状；20 例患者为偶然发现病变。影像学研究显示纵隔肿块增大，疑似恶性肿瘤。所有患者均接受了完全手术切除。肿瘤大小从 3.5 厘米至 24 厘米（中位数 10 厘米；平均值 10.46 厘米）。组织学检查显示胸腺组织小叶显示出发育良好的皮质-髓质结构，散在的 Hassall 小体被成熟的脂肪组织分隔，被薄的纤维囊包围。没有病例显示淋巴滤泡增生、细胞异型性或小叶融合的证据。免疫组织化学研究显示，在富含 CD3/TdT/CD1a 淋巴细胞的背景下，角蛋白阳性的胸腺上皮细胞呈正常分布模式。29 例最初的临床或病理诊断为胸腺瘤或胸腺瘤与胸腺增生。26 例的临床随访显示，所有患者在诊断后 5 至 15 年（平均 9 年）均存活且状况良好。对于引起正常胸腺显著增大并足以引起症状或令人担忧的影像学表现的胸腺实质增生，应在鉴别前纵隔肿块时考虑到这种疾病。本文提出了区分此类病变与富含淋巴细胞的胸腺瘤的标准。
