Discussion

The anterior mediastinum is the most common primary extragonadal site for seminoma. Of 307 cases reviewed in the English-language literature since 1956, we found only one case of posterior mediastinum (6) and one of middle mediastinum (7). Mediastinal seminoma is often associated with the thymus. Knapp et al. (8) reported a seminoma 2.5 cm in diameter completely surrounded by thymus tissue. Some authors called the tumor thymic seminoma (9,10), but it is uncertain whether mediastinal seminoma always arises in the thymus because, in many cases, the tumor was a bulky mass which included the thymus at diagnosis. In this case, we performed additional thymectomy to evaluate the thymus but found no connection between the tumor and the thymus.

Although the exact extragonadal germ cell tumor (EGCT) histogenesis is not known, several theories have been proposed. Friedman (2) postulated that all germ cell tumors originated from extragonadal, potentially biphasic germ cells left within the embryonic thymus. Lattes (11) and Schlumberger (12) suggested that germinal tumors arise from a maldevelopment of the thymic gland during embryogenesis. More recently, it has been suggested that germ cells are present in apparently ectopic sites in all healthy persons, having been distributed widely during normal embryogenesis, conveying genetic information or providing regulatory functions at somatic sites (13). In our case, it seems that the tumor was not associated with the thymus, so we think the first two hypotheses do not apply to our case.

The indication of orchidectomy is controversial in this case. A theory that an EGCT metastasizes from degenerated occult primary testicular tumors is not supported by the autopsy findings of Luna and Valenzuela-Tamariz (14). It is accepted that routine biopsy or orchidectomy is not needed in EGCT if no evidence exists for retroperitoneal involvement and no abnormality of the testicle is observed (14,15). Our case is in an unusual location for the tumor type and patient's age. Few cases have been reported where a mediastinal mass was found to be associated with testicular seminoma (16,17). For these reasons, we performed orchidectomy with the patient's agreement to evaluate the testes in detail.

In this case, we think the first operation was appropriate in order to diagnose the tumor in the middle mediastinum, but retrospectively the second operation was not necessarily needed, because the resected thymus was completely normal.

Current therapeutic recommendations for mediastinal seminoma are in transition. Traditional therapy has been initial surgical biopsy or debulking followed by radiation for localized disease (18). In spite of the high radiosensitivity, one third of patients relapsed, following radiotherapy, with distant metastases or marginal recurrences (19). Recent studies, in contrast, show good results when extragonadal seminoma was treated with chemotherapy (20-22). For mediastinal seminoma, an overall survival in excess of 80% can be expected with the use of chemotherapy, with or without radiotherapy (23). Chemotherapy has also been effectively used for very bulky seminomatous tumors. Generally, most clinicians now believe that surgery no longer plays a role in the definitive treatment of seminoma (24,25).

We obtained a good result with neoadjuvant chemotherapy in mediastinal seminoma in a 22-year-old male with Crohn's disease (26). Based on our experience and on previous reports, we selected postoperative chemotherapy with modified Einhorn's PVB therapy. Even though it is not certain that one cycle of chemotherapy will be enough to prevent recurrence in this case, we believe chemotherapy to be more effective than radiotherapy in preventing recurrence of seminoma.

We chose carboplatin instead of cisplatin owing to the slight disturbance of renal function seen with the use of cisplatin. Some authors reported good results for carboplatin-based chemotherapy in mediastinal (23) and testicular (27) germ cell tumors. Horwich et al. (28) recommended that carboplatin be considered the treatment of choice for advanced stages of seminoma when limitations of toxicity are considered important.

Our case demonstrated that mediastinal seminoma does not always occur in the anterior mediastinum of young males. Although this case is rare, seminoma should be included among the possible diagnoses of a middle mediastinal mass.