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Case Report |
1 Department of Radiology, Medical University of South Carolina, Box 250322, 169
Ashley Ave., Charleston, SC 29425.
2 Department of Surgery, Medical University of South Carolina, Charleston,
SC.
3 Department of Hematology/Oncology, Medical University of South Carolina,
Charleston, SC.
Received December 16, 2003;
accepted after revision February 4, 2004.
Address correspondence to J. G. Ravenel
(ravenejg{at}musc.edu).
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-fetoprotein level (5.3 ng/mL; normal, 0–20
ng/mL) and an elevated ß-HCG level (21 mIU/mL; normal, 0–4 mIU/mL).
Because of a suspicion of germ cell neoplasm, thoracoscopy was ultimately
performed to obtain sufficient tissue, and a diagnosis of seminoma was
made.
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After the diagnosis, testicular sonography was performed to look for an occult primary tumor. The testicles were normally positioned and symmetric in size and echogenicity, with two punctate calcifications in the right testicle. No mass was present. Given the association with Klinefelter's syndrome and the history of congenital anomalies, genetic karyotyping was performed and revealed a normal XY karyotype. The patient was treated with four cycles of etoposide and cis-platinum with a marked decrease in the size of the mass within the mediastinum and celiac lymph node and normalization of the ß-HCG level. Eight months after chemotherapy, the patient remained symptom- and tumor-free.
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Histologically, mediastinal seminomas are almost indistinguishable from seminomas arising in the testes. In most cases, because of the propensity of testicular seminomas to disseminate via lymphatics, studies are performed to exclude a testicular primary. However, remnant thymic tissue may be present in more than 25% of cases, and subtle immunohistochemical differences exist between mediastinal seminomas and their testicular counterparts [4]. These tumors are considered to be primary mediastinal tumors rather than metastases from an occult or burned out testicular primary tumor.
An increased incidence of testicular cancer exists in undescended testes. Germ cell neoplasms develop in 5–20% of undescended testes, and the risk is higher for abdominal testes than for inguinal testes [5]. However, if the testis is placed in the scrotum by orchiopexy or spontaneous migration by the age of 6 years, the risk of malignancy is very low. In our patient, the left testicle descended spontaneously at the age of 4 years, and neither physical examination nor sonography revealed evidence of a primary lesion.
Seminoma is the most frequent histologic subtype of malignant germ cell tumor, accounting for 40–65% of cases [6, 7]. These tumors typically occur in men from the second to fourth decades of life and may present as asymptomatic, incidentally discovered lesions in 20–30% of patients [1]. More frequently, these tumors cause symptoms because of the size and compression of adjacent structures, including the trachea and superior vena cava. The most common reported symptoms include chest pain, dyspnea, cough, and weight loss [3, 8]. Occasionally, serum HCG is elevated in seminoma [1, 8]. Metastatic disease occurs in fewer than half the cases; when it does occur, it is usually spread to adjacent lymph node groups in the neck, mediastinum, or abdomen. Hematogenous metastases are unusual but may be seen in lung, liver, and bone [8]. The prognosis for pure seminomas in the mediastinum is excellent, with a 5-year survival rate of more than 90%, with appropriate therapy.
On CT, mediastinal seminomas present as bulky, lobular anterior mediastinal masses that may encase or invade local structures [1]. In this regard, the imaging findings of our patient are similar to findings of seminomas in other locations. Calcification is distinctly unusual, but regions of cyst formation or cystic degeneration may be present. PET is usually not performed for staging germ cell neoplasms but was performed in this case because of the suspicion of lymphoma and was helpful in confirming spread to the large celiac lymph node.
Because of the tumor's location, a germ cell neoplasm was not our primary consideration. Our initial working diagnosis included lymphoma and a neurogenic tumor; the former was thought to be the likely diagnosis. Given the size and extensive nature of the mass, a schwannoma or neurofibroma seemed unlikely despite its growth into a single neural foramina. Ganglioneuroma was also considered but would be distinctly unusual at our patient's age.
Although other germ cell neoplasms have been described in the posterior mediastinum (mature teratomas, in particular) [1], to our knowledge, a primary posterior mediastinal seminoma has been described only once previously [9]. In this case, the individual was older than our patient, but the mass had a similar imaging appearance, with a confluent posterior mediastinal mass encasing the aorta.
It is not clear why a posterior mediastinal seminoma is so rare. If one accepts the theory of cells deposited along the migratory pathway, the posterior mediastinum should be involved more frequently as an intermediate point between the anterior mediastinum and the retroperitoneum. In a study of 104 patients, 50% of extragonadal seminomas arose within the retroperitoneum and 49% arose within the mediastinum [8]. Regardless, the response to chemotherapy of our tumor was similar to that of seminomas in other extragonadal locations.
In conclusion, despite the classic teaching that mediastinal seminomas arise solely in the anterior mediastinum, seminomas may originate in the posterior mediastinum. In patients in whom histopathologic examination of biopsy specimens from a posterior mediastinal mass is confusing, mediastinal germ cell tumor should be considered, and appropriate laboratory and immunohistochemical analysis should be performed.
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  Z.-G. Chen, H.-X. Pan, T. Wang, L.-E. Cai, Y.-Y. Lei, C.-H. Su, and H.-H. Luo Primary thymic seminoma in a 32-year-old female Ann. Onc., February 8, 2010; (2010) mdq023v1. [Full Text] [PDF]
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