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已有 713 次阅读2020-5-7 22:23 |个人分类:TET学习|系统分类:医学科学| 胸腺肿瘤, 精原细胞瘤


  Germ cell tumors (GCTs) occur primarily in the gonads; however, they have a predilection to arise from midline structures such as mediastinum, retroperitoneum, pineal gland, and sacral region forming a group designated as extragonal GCTs. Anterior mediastinum is the most common site for primary extragonadal GCTs. Primary mediastinal seminoma is usually located in the anterior mediastinum and affects young male. It constitutes 25% of all extragonadal GCTs. Seminoma is the second most common type of GCT of the mediastinum after mature teratoma.


  The most common tumors found in the anterior mediatinal compartment are of thymic, lymphatic or germ cell origin. More rarely masses associated with aberrant thyroid or parathyroid are found. GCTs of the mediastinum can be benign (mature teratoma) or malignant including seminomas, and nonseminomatous GCTs such as embryonal carcinoma, immature teratoma, yolk sac tumor, choriocarcinoma, or mixed GCTs.


  Some debate exists betwee n the origin of seminomatous and nonseminomatous GCTs. According to one theory, they develop from extragonadal yolk sac germinal cells whose normal migration along urogenital ridge to gonads was halted in the mediastinum.[4] Another theory suggests that they originate in the thymus due to its maldevelopment. Mediastinal seminoma is often associated with the thymus.


  Primary mediastinal seminoma is rare but well-defined disease which commonly affects young men. The diagnosis should be considered after exclusion of primary testicular tumor. The patients present with dyspnea, cough, fever, weight loss, and rarely superior vena cava syndrome.In most cases, these are detected incidentally, the patients being asymptomatic.


  The histomorphological features are usually indistinguishable from its gonadal counterpart. There are few case reports of mediastinal seminoma accompanied by secondary changes which may conceal the actual diagnosis as was seen in our case. These changes include reactive follicular hyperplasia, large cysts, epithelioid granulomas, and fibrosis. Our case was a diagnostic dilemma on microscopic examination as there were only focal areas showing neoplastic cells which were being masked by inflammatory cells along with florid granulomatous reaction.


  Mediastinal seminomas need to be differentiated from metastatic melanoma, thymoma, thymic carcinoma, Hodgkin disease, and anaplastic large cell lymphoma by use of ancillary techniques like immunohistochemistry (IHC), especially if the morphology of the original tumor is getting obscured.


  Many of these entities have also been reported with exuberant granulomatous reaction.[9] The complete panel of antibodies was used for IHC to discern the phenotype of the neoplastic cells. The diagnosis of the present case was established after IHC showed tumor cells to be strongly positive for PLAP, CD117, and D2-40. D2-40 gives diffuse membrane positivity in pure seminoma as well as positive staining in embryonal carcinoma hence embryonal carcinoma cannot be excluded by this marker. Besides D2-40 is not specific marker for Germinoma as it shares expression in mesothelial cells, lymphatic endothelium, and its neoplasm. D2-40 is also positive in adenxal tumors of the skin, adrenal cortical tumors, synovial sarcoma, embryonal carcinoma, etc., thus limiting its utility as a differential diagnostic marker in germ cell tumors as compared to Oct3/4 plus SOX2. However, PLAP is variably positive only in seminoma and was a good marker for differential diagnosis in our case. Oct3/4 and SOX2 markers were unavailable at our center.


  Metastasis in mediastinal seminomas is known to occur. Only 30–40% of patients are found to have localized disease. The most common behavior is an invasion into lungs and other intrathoracic structures. Treatment includes a combination of surgery and chemo-radiotherapy. Small tumors can be attempted for complete resection and postoperative radiotherapy of 40–45 Gy is curative. Cisplatin-based chemotherapy is known to induce complete response in patients with seminoma.Our patient responded to surgery along with chemotherapy and is presently on OPD follow-up at MDTC. This case highlights the importance of obtaining an adequate biopsy specimen.


  Thus, being a treatable tumor with a good prognosis early and correct diagnosis of mediastinal seminoma is of paramount importance. Secondary changes should not act as a deterrent in diagnosis and one should be vigilant enough while reporting on a small biopsy. A high index of suspicion by an astute pathologist and awareness of the secondary changes which can mask the primary lesion can help to clinch the diagnosis early.


  As some mediastinal masses such as lymphoma are not treated surgically, a diagnosis is often attempted on needle core or minimally invasive biopsies. These small biopsies may not be representative of the true lesion and depict only the peripheral secondary changes as was seen in our case.

图1:(a)正位胸片示肺门区轻度分叶的纵隔肿块。 (b)胸部CT增强显示前纵隔不均质肿块,未侵犯大血管

Figure 1: (a) Frontal chest radiograph showing a mildly lobulated mediastinal mass at the region of pulmonary bay. (b) Contrast enhanced computed tomography chest shows a heterogenous well-defined mass in the anterior mediastinum, not invading the great vessels

图2:大体标本显示多结节棕褐色卵形纵隔肿物,包膜不完整,外围边缘稍不规则,呈锐角; 切面质实,橡胶状坚硬

Figure 2: Gross specimen shows nonencapsulated multinodular tan-brown ovoid mediastinal mass with slightly irregular to sharp peripheral margins; the cut surface is solid and rubbery firm in consistency

图3:(a)纵隔肿块的镜下(×10)显示肉芽肿呈花斑样散在到融合。(b)高倍镜下可见肿瘤细胞散布在肉芽肿周围。 恶性细胞呈大多面体形态,胞质丰富,胞浆薄,核膜突出,核仁内可见粗大的染色质团,核膜明显,核仁呈骨架状突起。(c) CD117免疫染色显示精原细胞瘤细胞膜强阳性。

Figure 3: (a) Microscopic examination of the mediastinal mass (×10) shows florid discrete to confluent granulomas. (b) Higher magnification shows tumor cells interspersed and rimming these granulomas. The malignant cells appear to be of large polyhedral shape with abundant thin cytoplasm and round to oval vesicular nucleus with coarse clumped chromatin encircling clear areas in nucleoplasm, prominent nuclear membrane, and skein-like prominent nucleolus. (c) Immunostaining with CD117 shows strong membranous positivity in the seminoma cells

参考文献:Gupta D, Rath A, Rathi KR, Singh G. Primary thymic mediastinal seminoma with florid granulomatous reaction. Indian J Pathol Microbiol. 2016 Jul-Sep;59(3):351-4. doi: 10.4103/0377-4929.188113. PubMed PMID: 27510675.





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回复 hyc3140 2020-5-21 19:10
恶性生殖细胞瘤与侵袭性胸腺瘤、胸腺癌及淋巴瘤难以鉴别Mediastinal seminoma mimicking invasive
thymoma on 18F-FDG PET/CT
回复 hyc3140 2020-5-21 19:22


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