대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Seminoma (malignant germ cell tumor)

Radiologic Findings

Chest radiograph shows left mediastinal widening.
CT scans show an anterior mediastinal mass with relatively homogeneous attenuation.
The serum tumor markers (AFP, HCG) were not elevated.

Brief Review

Seminoma is the next most frequent (25-40%) mediastinal germ cell tumor after teratoma and occurs almost exclusively in men (90%), whose average age at presentation is about 30 years.

Pathologically, the tumor is composed of nests of clear or vacuolated cells separated by a variably thick fibrovascular stroma containing numerous lymphocytes. This pathologic findings are same as testicular seminoma, ovarian dysgerminoma or germinoma.


Approximately 30 % of patients are asymptomatic at the time of initial diagnosis. When present, symptoms are usually derived from pressure or invasion of vascular structures within mediastinum. The serum tumor markers (AFP, HCG) are not elevated.

Radiographically, seminomas usually appear as a lobulated non-calcified mass that cannot be distinguished from other malignant germ cell tumors. CT shows mildly enhancing homogeneous soft tissue mass with a few areas of low attenuation. The adjacent mediastinal fat planes may be obliterated and extensive local invasion may be identified. Also superior vena caval obstruction is not uncommon. The differential diagnosis includes lymphoma of the thymus, metastatic carcinoma, and other primary malignant tumors arising in the anterior mediastinum.

Non-seminomatous malignant germ cell tumors, namely the endodermal sinus tumors (EST), choriocarcinomas, and embryonal carcinomas, are not only more aggressive lesions than their seminomatous counterparts, but they are also more aggressive when compared with their identical histologic testicular counterparts. Great majority of patients with malignant germ cell tumors are symptomatic; cough, dyspnea, chest pain, and not uncommonly superior vena caval (SVC) syndrome.

ESTs, the rarest of the germ cell tumors, secret alpha-fetoprotein (AFP) and tumor activity is strongly correlated with the serum level. Human chorionic gonadotropin is detectable in some cases of EST; however, it is generally accepted that this endocrinopathy is due to small foci of choriocarcinoma or embryonal carcinoma within the EST.

CT has been useful in differentiating between the non-seminomatous and seminomatous germ cell tumors. Seminomas have been described as large, sharply demarcated masses that are usually of homogeneous attenuation. Chest wall invasion is rare, as is the development of pleuropericardial effusion.


In contrast, non-seminomatous tumors are of heterogeneous attenuation. The areas of lower attenuation within the tumors are due to necrosis and hemorrhage. A strong tendency for bony invasion and fat plane obliteration exists. Thick capsules that enhance after IV administration of contrast material have been described. Rarely coarse tumor calcification may be evident. Pleural effusion are more common.

Although CT may be helpful in differentiating between the two subtypes of germ cell tumors, its use in differentiating germ cell tumor from other tumors of the anterior mediastinum is more questionable. Thymomas, carcinoid tumors, lymphoma, and mediastinal metastases must also be considered in the differential diagnosis of heterogeneous anterior mediastinal masses.

References

1. Armstrong P. Mediastinal and hilar disorder. In: Armstrong P, Wilson AG, Dee P, Hansell DM. eds. Imaging of diseases of the chest. 2nd ed. St. Louis; Mosby, 1995;732-736

2. Fraser RS, Pare JAP, Fraser RG, Pare PD. Synopsis of diseases of the chest. 2nd ed. Philadelphia; W.B. Saunders, 1994;911-915

3. Lee KS, Im JG, Han CH, Kim CW, Kim WS. Malignant primary germ cell tumors of the mediastinum : CT features. AJR 1989 ; 153 : 947-951

4. Moran CA, Suster S, Koss MN. Primary germ cell tumors of the mediastinum III. yolk sac tumor, embryonal carcinoma, choriocarcinoma, and combined nonteratomatous germ cell tumors of the mediastinum - a clinicopathologic and immunohistochemical study of 64 cases. Cancer 1997 ; 80 : 699-707

5. Romo LV, Parker DR. Chest case of the day; endodermal sinus tumor of the mediastinum. AJR 1991; 156: 1297-9

6. Kim JS, Joo YG, Kim H, Zeon SK, Suh SJ. Computed tomography of primary mediastinal seminoma: two case reports. J Korean Radiol Soc 1988;25:762-766

Keywords

Mediastinum, Malignant tumor,