J Pathol Transl Med.  2017 Mar;51(2):165-170. 10.4132/jptm.2016.08.24.

Thymoma and Synchronous Primary Mediastinal Seminomas with Florid Follicular Lymphoid Hyperplasia in the Anterior Mediastinum: A Case Report and Review of the Literature

Affiliations
  • 1Department of Pathology, Gyeongsang National University Changwon Hospital, Changwon, Korea.
  • 2Department of Thoracic and Cardiovascular Surgery, Gyeongsang National University Hospital, Jinju, Korea.
  • 3Gyeongsang National University School of Medicine, Jinju, Korea. jhlee7@gnu.ac.kr
  • 4Institute of Health Science, Gyeongsang National University, Jinju, Korea.
  • 5Department of Radiology, Gyeongsang National University Changwon Hospital, Changwon, Korea.
  • 6Department of Pathology, Gyeongsang National University Hospital, Jinju, Korea.

Abstract

Thymoma is the most common neoplasm of the anterior mediastinum and has malignant potential. Germ cell tumors (GCTs) found in the anterior mediastinum are usually benign, and malignant GCTs, such as seminomas, are rare. Histologically, mediastinal seminoma is indistinguishable from testicular seminoma except for site-associated morphological features such as lymphoid follicular hyperplasia. Therefore, excluding metastasis is very important. Recently, we treated a young adult patient with multiple thymic masses that occurred simultaneously. The patient underwent a thymectomy for the removal of the mediastinal masses, one of which was diagnosed as type B2 invasive thymoma, and two of which were diagnosed as primary mediastinal seminomas with massive follicular hyperplasia. The patient received adjuvant chemotherapy after surgical resection. To our knowledge, this is the first description of a thymoma and a mediastinal seminoma occurring simultaneously in the thymus. We present this case along with a literature review.

Keyword

Thymoma; Seminoma; Mediastinum; Follicular hyperplasia

Figure

  • Fig. 1. Radiologic findgings of the anterior mediastinal masses. (A) Maximum intensity projection image of fluorodeoxyglucose–positron emission tomography/computed tomography (PET/CT) shows two faint hypermetabolic foci in the anterior mediastinum. The larger one (short arrow) is 4.8 cm (standard uptake value [SUV], 3.3) and the smaller one (long arrow) is 2.0 cm (SUV, 3.4). The smaller one looks like single mass due to limited spatial resolution of PET/CT image (coronal view). (B, C) Axial contrast enhanced chest CT images show multiple tumors in the anterior mediastinum; about 5-cm-sized mass (thymoma, arrow) compressing superior vena cava (B) and 1.5 cm-sized nodule (seminoma, arrows) (C).

  • Fig. 2. Macroscopic findings of the thymectomy specimen. Three well circumscribed round masses are seen. The largest one is thymoma and two small round masses (arrows) are seminomas. The seminomas are 1.5 cm and 0.5 cm apart from the thymoma.

  • Fig. 3. Histologic findings and immunohistochemical staining results of the thymoma and seminoma of the anterior mediastinal masses. (A) At low power, thymoma shows relatively well demarcated round lobulated mass separated by thick collagenous blands consisting of dual population of lymphocytes and epithelial cells. (B) The epithelial cells show a bland appearance; round to oval with vesicular nuclei, eosinophilic to amphophilic cytoplasm, and small inconspicuous nucleoli. (C) Mediastinal seminoma show numerous lymphoid follicles with germinal center and microcystic change in left area. Seminoma component is seen in right area. (D) Seminoma cells displaying their classical features; indistinct cell border, clear to eosinophilic cytoplasm, vesicular nuclei with eosinophilic nucleoli, and increased mitotic activity. (E) CD117 staining reveals negative reaction for epithelial component of thymoma. (F) Thymic epithelial cells of thymoma highlighted by a cytokeratin 19 immunostain. (G) CD117 staining confirming a diagnosis of seminoma. (H) Cytokeratin 19 staining demonstrates thymic remnant associated with cystic change but is negative for seminoma component around thymic remnant.


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