胸腺病变：图文综述

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B） 胸腺癌
胸腺癌占胸腺上皮肿瘤的20%，通常缺乏包膜。与胸腺瘤相比，侵袭性特征更为常见。大约50-65%的患者在诊断时出现远处转移，胸膜转移常见（图16）。胸腺癌分为各种亚型，最常见的包括鳞状细胞癌（36%）、淋巴上皮瘤样癌（32%）和未分化癌（11%）[1]。B) THYMIC CARCINOMA
Thymic carcinoma accounts for 20% of thymic epithelial neoplasms and usually lacks a capsule. Aggressive features such as invasion are more common, compared to thymoma. Approximately 50-65% of patients present with distant metastases at the time of diagnosis, and pleural metastases are frequent (figure 16). Thymic carcinoma englobes various subtypes, the most common include squamous cell (36%), lymphoepithelioma-like (32%), and undifferentiated (11%) [1].

图16：女，67岁。增强CT显示胸腺鳞状细胞癌（黄色箭头）伴多处肝转移。
Fig 16: Female, 67 years old. Contrast-enhanced CT demonstrates thymic squamous cell carcinoma (yellow arrow) with several hepatic metastases.

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C） 胸腺淋巴瘤
淋巴瘤累及胸腺的病例多见于播散性疾病（+霍奇金病，组织学结节硬化）。偶尔也会发生孤立的胸腺受累。
可能很难与其他胸腺肿块区分开。CT上通常表现为弥漫性肿大、单一优势肿块或多个独立肿块（图17）。相关纵隔淋巴结病，尤其是年轻患者，提示纵隔淋巴瘤[1,2]。淋巴瘤和GCT往往大于胸腺瘤或良性病变[1]。

C) THYMIC LYMPHOMA
Thymic involvement with lymphoma occurs more frequently with disseminated disease (+ Hodgkin disease, with histologic nodular sclerosis). Occasionally, isolated thymic involvement may happen.

It may be difficult to distinguish from other thymic masses. On CT it usually shows diffuse enlargement, a single dominant mass, or multiple separate masses (figure 17). Associated mediastinal lymphadenopathy, especially if a young patient, is indicative of mediastinal lymphomas [1,2]. Lymphoma and GCT tend to be larger than thymomas or benign lesions [1].

图17：4岁男孩。A和B：纵隔内均匀的软组织衰减肿块，明显增大（橙色箭头）。C和D：右侧为肿大淋巴结融合，中心位于右肺门，向上延伸至右气管旁区（蓝色箭头）。组织学显示为急性T淋巴细胞性淋巴瘤。与纵隔淋巴结病相关的胸腺增大，特别是年轻患者，提示纵隔淋巴瘤。
Fig 17: 4-years-old boy. A and B: Homogeneous soft-tissue attenuation mass in the mediastinum, with markedly increased dimensions (orange arrows). C and D: Adenopathic conglomerate on the right, with epicenter in the right pulmonary hilum, which extends superiorly to the right paratracheal region (blue arrows). Histology revealed acute T cell lymphoblastic lymphoma. Enlargement of the thymus associated with mediastinal lymphadenopathy, especially if a young patient, is indicative of mediastinal lymphomas.

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D） 胸腺类癌
胸腺类癌是一种罕见的神经内分泌肿瘤，几乎都是非典型的。这些肿瘤发生在MEN I，比其他发生在胸部的类癌更具侵袭性。复发转移率高，预后差。它们可能在CT上显示坏死或出血区域以及细小的钙化[2]。
三、 其他罕见病变
如图3-表1所示。
转移性病变：最常见的原发性肿瘤包括肺癌、甲状腺癌、乳腺癌和前列腺癌[2]。
朗格汉斯细胞组织细胞增生症
生殖细胞瘤：发生在胸腺周围或胸腺内。畸胎瘤是最常见的类型，表现为肉眼可见的脂肪和钙化（占所有GCT的70%）（图18）。非畸胎瘤性GCT是罕见的，通常发生在年轻男性。

D) THYMIC CARCINOID
Thymic carcinoid is a rare neuroendocrine tumor, and virtually all are atypical. These tumors occur in the setting of MEN I and are much more aggressive than other carcinoid tumors that arise elsewhere in the thorax. Poor prognosis due to high recurrence and metastatic disease. They may demonstrate on CT areas of necrosis or hemorrhage and fine calcifications [2].

III. OTHER RARE LESIONS

Listed in figure 3 - table 1.

Metastatic lesions: the most common primary tumors include the lung, thyroid, breast, and prostatic carcinoma[2].
Langerhans cell histiocytosis
Germ cell tumors (GCTs): develop around or within the thymus. Teratoma is the most common type, demonstrating macroscopic fat and calcification (70% of all GCT) (figure 18). The non-teratomatous GCTs are rare and usually occurs in young males.

图18：13岁男孩，成熟畸胎瘤。正位胸片显示右纵隔分叶状高密度影，占右下半胸的2/3。MRI显示T2-W FS（B）和增强T1-W（C）中有一个不均匀肿块,有包膜，并伴有多个囊性区域。镜下示囊性肿瘤由三个胚层的成熟组织组成（H&E，40x）。
Fig 18: Mature teratoma in a 13 years old boy. A – Frontal chest x-ray reveals a lobulated right mediastinal opacity that occupies the 2/3 of the inferior right hemithorax. MRI shows a heterogeneous mass, encapsulate, in T2-W FS (B) and contrast-enhanced T1-W ( C ), with multiple cystic areas. D- Photomicrograph shows cystic tumor consisting of mature tissues derived from the three germ layers (H&E, 40x).

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3.成像技术-胸腺病变的良恶性特征
影像学在前纵隔病变的定性中起着关键作用。
胸部X线是怀疑前纵隔肿块的首次成像技术。如果病变较大，通常表现为软组织肿块[1]。
通常，CT被认为是前纵隔肿块定性和疾病分期的首选方法。由于高空间分辨率，CT显示疾病的扩展及其与邻近结构的关系。
磁共振成像的作用继续拓展。这是一种有效区分前纵隔恶性肿瘤和良性病变的方法，可安全用于年轻患者[1]。
表5（图19）试图总结不同成像方式下胸腺病变良恶性特征的差异。

3. IMAGING TECHNIQUES - BENIGN AND MALIGNANT FEATURES OF THYMIC LESIONS
Imaging plays a pivotal role in the characterization of a lesion located in the anterior mediastinum.

Chest X-ray is the first imaging technique to implement in case of an anterior mediastinal mass suspicion. If the lesion is large it usually appears as an extra soft tissue mass or opacity[1].

Typically, CT is considered the modality of choice for the characterization of an anterior mediastinal mass and staging the disease. Due to high spatial resolution, CT demonstrates the extension of the disease and its relationship to adjacent structures.

The role of MRI continues to expand. It is a modality that allows with effectiveness distinguish malignant tumors from benign lesions in the anterior mediastinum and can be safely used in younger patients[1].

Table 5 (figure 19) tries to summarize the differences between benign and malignant features of thymic lesions considering the different imaging modalities.


图19：表5：不同技术下胸腺良恶性病变的影像学特征。
Fig 19: Table 5. : Imaging features of benign and malignant thymic lesions in the different techniques.

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结论
放射科医师应熟悉不同胸腺病变的影像学特点，以达到准确诊断、充分随访，并指导最终需要的介入治疗。
计算机断层扫描（CT）对于前纵隔肿块的定性是必不可少的，因为它可以评估其组织成分、形态、大小、血管化程度，并评估周围纵隔结构的最终侵犯。
在过去的几年里，磁共振成像已经显示出越来越大的作用。
有创性的术前诊断通常保留在有创性纵隔病变和可疑淋巴增生性疾病的患者。
Conclusion

• Radiologists should be familiar with the imaging characteristics of different thymic lesions to achieve an accurate diagnosis, adequate follow-up, and also guide the eventual need for intervention.
• Computed tomography (CT) is essential for the characterization of an anterior mediastinal mass since allows the evaluation of its tissular component, morphology, size, degree of vascularization, and assessment of the eventual invasion of the surrounding mediastinal structures.
• In the last years, MRI has been showing an expanding role.
• The invasive preoperative diagnosis is usually reserved for patients with invasive mediastinal lesions and those with suspected lymphoproliferative disease.
  

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References

• Gentili F, Pelini V, Lucii G, Luzzi L, Mazzei FG, Fausto A, Volterrani L, Mazzei MA. Update in diagnostic imaging of the thymus and anterior mediastinal masses. Gland Surg. 2019 Sep;8(Suppl 3):S188-S207
• Goldstein, A. J., Oliva, I., Honarpisheh, H., & Rubinowitz, A. (2015). A Tour of the Thymus: A Review of Thymic Lesions With Radiologic and Pathologic Correlation. Canadian Association of Radiologists Journal, 66(1), 5–15.
• Nishino M, Ashiku SK, Kocher ON, Thurer RL, Boiselle PM, Hatabu H. The thymus: a comprehensive review. Radiographics. 2006 Mar-Apr;26(2):335-48. doi: 10.1148/rg.262045213. Erratum in: Radiographics. 2017 May-Jun;37(3):1004.
• Hussein, S.A., Sabri, Y.Y., Fouad, M.A. et al. Role of different imaging modalities in the evaluation of normal and diseased thymus. Egypt J Bronchol 14, 5 (2020)
• Ackman J, Kovacina B, Carter B, et al. Sex difference in normal thymic appearance in adults 20-30 years of age. Radiology 2013;268:245e53.
• Marx, A., Chan, J. K. C., Coindre, J.-M., Detterbeck, F., Girard, N., Harris, N. L., … Ströbel, P. (2015). The 2015 World Health Organization Classification of Tumors of the Thymus: Continuity and Changes. Journal of Thoracic Oncology, 10(10), 1383–1395.
  

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Congress:ECR 2021
Poster Number:
C-13863
Type:
Educational Exhibit
Keywords:
Tissue characterisation, Pathology, Neoplasia, Surgery, Diagnostic procedure, Biopsy, PACS, MR, CT, Thorax, Mediastinum, Anatomy
Authors:
P. D. S. Freitas, S. F. Alves, J. D. Santos, P. Santos; Lisboa/PT
DOI:
10.26044/ecr2021/C-13863
DOI-Link:
https://dx.doi.org/10.26044/ecr2021/C-13863
https://epos.myesr.org/poster/esr/ecr2021/C-13863