Mediastinal non-seminomatous germ cell tumours: their association with non-germ cell malignancies

Primary germ cell tumours of the mediastinum: A review with emphasis on diagnostic challenges

This article will review current aspects of the histopathological, immunohistochemical and molecular analysis of primary mediastinal germ cell tumours (PMGCTs) as well as their aetiological, epidemiological, clinical and therapeutic features. PMGCTs represent an important differential diagnosis in the spectrum of mediastinal tumours, and their diagnosis is usually made on small tissue samples from core needle biopsies in combination with diagnostic imaging and serum tumour markers. As in lymphomas, a small biopsy is often the only viable tumour sample available from these patients, as they receive chemotherapy prior to eventual surgical resection. Pathologists therefore need to apply an efficient combination of immunohistochemical markers to confirm the diagnosis of a PMGCT and to exclude morphological mimics.

MRI Findings and Differential Diagnosis of Anterior Mediastinal Solid Tumors

The anterior mediastinum is the most common location of mediastinal tumors, and thymic epithelial tumors are the most common mediastinal tumors. It is important to differentiate thymic epithelial tumors from malignant lymphomas and malignant germ cell tumors because of the different treatment strategies. Dynamic contrast-enhanced MRI and diffusion-weighted imaging can provide additional information on the differential diagnosis. Chemical shift imaging can detect tiny fat tissues in the lesion and is useful in differentiating thymic hyperplasia from other solid tumors such as thymomas. MRI findings reflect histopathological features of mediastinal tumors, and a comprehensive evaluation of MRI sequences is important for estimation of the histopathological features of the tumor. In this manuscript, we describe the MRI findings of anterior mediastinal solid tumors and the role of MRI in the differential diagnosis.

Extragonadal germ cell tumors: a review with emphasis on pathologic features, clinical prognostic variables, and differential diagnostic considerations

Extragonadal germ cell tumors (GCTs) are relatively uncommon, but represent 1% to 5% of all GCTs. Their morphology varies widely and includes mature teratoma, immature teratoma, seminoma, yolk sac tumor, embryonal carcinoma, choriocarcinoma, and mixed GCTs. Noncentral nervous system extragonadal GCTs are found in a variety of anatomic locations, but most commonly affect the mediastinum and sacrococcygeal region. Predicting behavior in these tumors can be confusing because it is based on a combination of varying factors including patient age, histologic subtype, anatomic site, and clinical stage. This review attempts to dissect these issues by separating the discussion into 3 age groups: neonatal (congenital), children (prepubertal), and adult (postpubertal). Within each individual age group, we cover the significance of anatomic site, morphology, and staging parameters. In addition, we discuss the spectrum of associated secondary malignancies and their impact on patient outcome. Finally, we provide a detailed survey of differential diagnostic considerations grouped by anatomic site.

Hepatoid Thymic Carcinoma

We describe the clinicopathologic findings in a so far unrecognized thymic tumor. The tumor occurred in a 70-year-old woman with respiratory distress but neither myasthenia gravis nor other symptoms. Metastases or another primary tumor were absent. The well-circumscribed neoplasm was located in the thymic region, measured 18 x 12 x 8 cm, and showed a homogeneous, tan-colored, soft cut surface. By histology, the tumor lacked a true capsule and a lobular growth pattern, was almost devoid of stroma, and infiltrated among remnant thymus lobules. The polygonal tumor cells formed solid sheets, trabeculae, or occurred as single cells that resembled hepatocytes. Proliferative activity was low. Portal structures, sinuses, and bile were absent as were areas of conventional thymoma, adenocarcinoma, or germ cell tumor. The tumor expressed cytokeratins 7 and 19, alpha1-antitrypsin, alpha1-antichymotrypsin, and hep-Par-1. Alpha-fetoprotein (AFP), human beta-chorionic gonadotropin (beta-HCG), placental alkaline phosphatase, CD5, CD30, CD31, CD34, CD45, CD68, CD99, S-100, HMB45, desmin, actin, or neuroendocrine markers were not expressed, and intratumorous CD1a+ or TdT+ immature T cells were absent. AFP was repeatedly undetectable in the blood. Mediastinal tumor recurrence was detected 6 months after surgery. Following radiochemotherapy, the patient has remained free of disease for 26 months. We conclude that this tumor is a thymic carcinoma (WHO type C thymoma). A diagnosis of hepatoid yolk sack tumor appears unlikely considering absence of a bona fide germ cell component, lack of AFP expression, and the patient's female gender. Because of its morphologic and immunohistochemical features, we propose the term "hepatoid thymic carcinoma" for this new type of thymic carcinoma.