Mediastinal seminoma associated with multilocular thymic cyst
© The Author(s). 2017
Received: 18 September 2016
Accepted: 16 December 2016
Published: 5 January 2017
An asymptomatic 26-year-old man received an annual medical check-up, and chest X-ray showed a protrusion of the aortopulmonary window. Chest computed tomography (CT) revealed an anterior mediastinal tumor and cysts with thin wall and septum enhancement. The preoperative diagnosis was cystic thymoma or malignant lymphoma. We performed total resection of the tumor through a median sternotomy. The pathological findings revealed seminoma, positive for c-kit stain, and multilocular thymic cysts. Cysts were lined by normal squamous epithelium and no seminoma cells were located on their surface. So, cysts were probably secondary changes caused by seminoma cells themselves or inflammatory stimulations. No invasion to adjacent structures was seen. After the surgery, testicular ultrasound imaging and abdominal, pelvic, and cerebral CT showed no apparent tumor or enlarged lymph nodes; however, an abnormal uptake in the right mesenteric lymph node was pointed out by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) scan. The patient received four courses of bleomycin, etoposide, and cisplatin (BEP) as adjuvant chemotherapy. Follow-up PET scan revealed no uptake in the right mesenteric lymph node. To date, no recurrence or metastasis has been identified for 16 months.
Prominent cystic change of mediastinal seminomas in patients is uncommon and rarely reported, and those cases that are reported show only unilocular cystic changes. Here, we present a patient with a mediastinal seminoma with multilocular thymic cysts. It is probable that primary seminoma caused the cyst formation of the thymus.
Mediastinal germ cell tumors account for only 1 to 5% of all germ cell tumors . Seminomas account for only 0.4% of all mediastinal neoplasm in adults, and most are typically solid and lobulated in appearance [3, 4]. Only a few mediastinal seminomas showed prominent cystic changes, and most of those were unilocular and congenital. However, this case showed multilocular cystic changes, lined by normal squamous epithelium. So, these cysts were probably secondary ones caused by seminoma cells themselves or inflammatory stimulations. The pathogenesis of cystic changes in seminoma is still unclear but thought to be related to the irritation that tumor cells cause to Hassall corpuscles . The process has been observed frequently as a secondary event complicated with a variety of thymic neoplasms, including thymoma, non-Hodgkin’s lymphoma, Hodgkin’s disease, and germ cell tumor (mainly mature cystic teratoma) [6, 7]. Initial management of primary mediastinal seminoma is cisplatin-based chemotherapy ; however, because of its rarity, some cases are diagnosed only after surgical resection. Fine needle aspiration cytology occasionally helps the preoperative diagnosis . In this case, however, cyst walls were thin and solid lesions were located behind the left lung, so it was thought to be difficult to perform. According to International Germ-Cell Cancer Collaborative Group risk classification, the patient is classified as intermediate risk group to undergo chemotherapy. Four courses of BEP were administered as chemotherapy, which will result in a more favorable prognosis [10, 11]. When an anterior mediastinal tumor with multilocular cystic changes is observed, primary seminoma also should be listed as a differential diagnosis.
Primary mediastinal seminoma should be listed as one of the differential diagnoses, when anterior mediastinal tumor with unilocular cyst is confirmed, especially the patient is young male.
We thank Hidenori Kage and Akihisa Mitani at the Department of Internal Medicine of Respirology, The University of Tokyo Hospital, for their advice on postoperative management.
This work was not supported by any funding or support.
MI and JN performed the operation for this case. MI drafted the manuscript. JN performed the statistical analysis. MI, JN, TY, NH, KN, MA, MS, and JN participated in the design of the study. JN conceived of the study and participated in its design and coordination. ST, AS-U, MF reviewed the pathological findings. TW reviewed the radiological findings. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Written informed consent was obtained from the patient for publication of this case report and the accompanying images.
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