Introduction: With the use of ultrasonography for the evaluation of thyroid and nonthyroid neck diseases, the incidental discovery of previously unsuspected thyroid nodules/nonpalpable lesions has increased. Intrathyroidal thymus arises due to aberrant thymic migration during embryogenesis. It is thought to be rare, fulfils the classiccriteria for diagnosis of an incidentaloma and it can be mistaken for a thyroid nodule. Multinodular goiter is the main endocrine manifestation of DICER1 syndrome, a tumor predisposition syndrome. Careful thyroid examination including ultrasound is thus necessary for DICER1 syndrome patients. Case Report: A 4-year-old prepubertal boy was referred to the pediatric endocrinology department following an earlier diagnosis of pleuropulmonary blastoma (PPB) type III, which is a hallmark component of DICER1 syndrome. The patient underwent surgery followed by chemotherapy. Genetic analysis identified a germline DICER1 pathogenic variant (c.2062C#x3e;T, p.R688*)in the child and in 5 relatives. A second somatic DICER1 RNase IIIb hotspot mutation(c.5438A#x3e;G, p.E1813G) was identified in DNA extracted from the proband’s PPB. He had no goiter on clinical examination, but a heterogenous, well-delineated, avascular, solid and hypoechogenic lesion with pseudomicrocalcifications was observed in the right lobe (4.1 × 3.1 × 2.6 mm), suggestive of thyroid neoplasia. Diagnostic work-up and a 3-year follow-up excluded thyroid neoplasia and confirmed the diagnosis of an intrathyroid benign thymic lesion. Discussion and Conclusion: This case exemplifies that thyroid incidentalomas in DICER1 syndrome patients should be viewed with great suspicion, but that not all thyroid disorders are indeed DICER1-related in these patients.
Eur Thyroid J

中文翻译：

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甲状腺内胸腺（偶发瘤）模拟 DICER1 综合征中的甲状腺瘤

简介：随着超声检查用于评估甲状腺和非甲状腺颈部疾病，偶然发现先前未曾怀疑的甲状腺结节/不可触及病变的情况有所增加。甲状腺内胸腺是由于胚胎发生过程中的异常胸腺迁移而产生的。它被认为是罕见的，实现了经典偶发瘤的诊断标准，它可能被误认为是甲状腺结节。多结节性甲状腺肿是肿瘤易感综合征DICER1综合征的主要内分泌表现。因此，DICER1 综合征患者需要进行仔细的甲状腺检查，包括超声检查。病例报告：一名 4 岁青春期前男孩在早期诊断为 III 型胸膜肺母细胞瘤 (PPB) 后被转诊至儿科内分泌科，这是 DICER1 综合征的标志性组成部分。患者接受了手术，随后接受了化疗。遗传分析确定了种系DICER1致病性变异 (c.2062C#x3e;T, p.R688*)在孩子和 5 个亲戚中。第二个体细胞DICER1 RNase IIIb 热点突变(c.5438A#x3e;G, p.E1813G) 在从先证者的 PPB 中提取的 DNA 中得到鉴定。临床检查他没有甲状腺肿，但在右叶 (4.1 × 3.1 × 2.6 mm) 观察到异质性、轮廓清楚、无血管、实性和低回声病变，伴有假性微钙化，提示甲状腺瘤。诊断性检查和 3 年随访排除了甲状腺瘤并确认了甲状腺内良性胸腺病变的诊断。讨论和结论：该病例表明，应高度怀疑 DICER1 综合征患者的甲状腺偶发瘤，但并非所有甲状腺疾病都确实与这些患者的DICER1相关。
欧洲甲状腺杂志