Adenomatoid Spindle Cell Thymomas: A Clinicopathological and Immunohistochemical Study of 20 Cases

Atypical thymoma (epithelial-rich thymoma, well-differentiated thymic carcinoma, WHO type B3 thymoma): A conundrum

Thymomas composed predominantly of epithelioid tumor cells with scattered lymphocytes have been well recognized in the literature. This subtype of thymoma has been variously termed epithelial-rich thymoma, well-differentiated thymic carcinoma, atypical thymoma, or World Health Organization (WHO) type B3 thymoma. Regardless of the designation however, these tumors are known to show a spectrum of histopathological growth patterns that may pose challenges in interpretation and diagnosis, particularly when dealing with small mediastinoscopic biopsies. Just like any other type of thymoma, those composed predominantly of epithelioid cells may present as encapsulated or invasive tumors. Nevertheless, compared to other subtypes of thymoma, they are uncommon neoplasms. Therefore, it becomes very important to sufficiently sample thymomas before making a diagnosis of a particular subtype, especially when the tumor is rich in epithelioid cells and only has a scant lymphocytic component. Because of the unusual occurrence of these tumors, there are only few large series of cases that attempt to highlight not only the more salient histopathological features but also the most important immunohistochemical and molecular characteristics.

Thymoma: Histologically a heterogenous group of tumors

Over the years the nomenclature of thymomas has been debated regarding the best manner in which these tumors should be grouped. In every schema presented thus far, the main issue has been the presence or lack of lymphocytes and accordingly, the tumors have been place into a specific category. However, even though this concept applies for most of the cases, there are numerous tumors that do not necessarily fit into those categories as either the thymomas show another cellular proliferation associated with the epithelial cells or the epithelial cell themselves are arranged in a pattern that departs from the conventional features of the classic thymoma. Herein we will emphasize those features, which in some circumstances, mainly with small mediastinoscopic biopsies may pose a considerable problem in interpretation. We do consider that the most important issue is to be familiar with the different growth pattern that these tumors may show in order to avoid misdiagnosis. In addition, we consider that regardless of the growth pattern or cellular composition of the tumor, it is highly recommended that these tumors just like any other be carefully sampled and properly stage. Although we are fully aware of the different growth pattern and specific cellular details that thymoma may show, the discussion of each one of those tumors is beyond the scope of this review. Therefore, we have placed more emphasis in those, which in our judgment are more commonly encountered in the daily practice.

Adenomatoid Tumor: A Review of Pathology With Focus on Unusual Presentations and Sites, Histogenesis, Differential Diagnosis, and Molecular and Clinical Aspects With a Historic Overview of Its Description

Adenomatoid tumors have been described almost a century ago, and their nature has been the subject of debate for decades. They are tumors of mesothelial origin usually involving the uterus, the Fallopian tubes, and the paratesticular region. Adenomatoid tumors of the adrenal gland, the liver, the extragenital peritoneum, the pleura, and the mediastinum have been rarely reported. They are usually small incidental findings, but large, multicystic and papillary tumors, as well as multiple tumors have been described. Their pathogenesis is related to immunosuppression and to TRAF7 mutations. Despite being benign tumors, there are several macroscopic or clinical aspects that could raise diagnostic difficulties. The aim of this review was to describe the microscopic and macroscopic aspects of adenomatoid tumor with a special focus on its differential diagnosis and pathogenesis and the possible link of adenomatoid tumor with other mesothelial lesions, such as the well-differentiated papillary mesothelioma and the benign multicystic mesothelioma, also known as multilocular peritoneal cysts.

Intrathoracic glomus tumors and glomangiosarcomas: a clinicopathological and immunohistochemical study of 14 cases with emphasis on anatomic distribution

Fourteen cases of primary intrathoracic glomus tumor and glomangiosarcoma are presented. The patients were 9 men and 5 women aged 36 to 63 years (mean, 49.5 years). Clinically, 11 patients presented with nonspecific symptoms including cough, hemoptysis, chest pain, and back pain while 3 patients were asymptomatic. Anatomically, 9 tumors were in an intrapulmonary location, 3 in the mediastinum, and 2 in the trachea. Surgical resection was performed in all cases, and grossly the tumors varied in size from 1.5 to 4.5 cm in greatest diameter. Histologically, 12 cases corresponded to glomus tumor characterized by a homogenous proliferation of medium-sized cells with round nuclei and inconspicuous nucleoli and no evidence of mitotic activity or necrosis. In 2 cases, the presence of marked cellular pleomorphism, nuclear atypia, and mitotic activity was more in keeping with a diagnosis of glomangiosarcoma. The 2 glomangiosarcomas were located in the lung, one of which was associated with lymph node metastasis. Immunohistochemical stains for smooth muscle actin were positive in all cases while negative for epithelial, vascular, neuroendocrine, and neural markers. Clinical follow-up showed that all patients with a glomus tumor are alive and well after a period of 12 to 36 months after surgical resection. In contrast, the 2 patients with glomangiosarcoma died of tumor 24 and 36 months, respectively, after initial diagnosis. The current cases highlight the ubiquitous distribution of these tumors within the thoracic cavity and stress the importance of including these tumors in the differential diagnosis of thoracic neoplasms.

Immunohistochemistry in the diagnosis of thymic epithelial neoplasms

The diagnosis of thymic epithelial neoplasms is normally rendered after careful evaluation of their histologic features. In some cases, however, the morphological heterogeneity or overlap with neoplasms of other organ systems can lead to diagnostic uncertainty. On the basis of this, the use of immunohistochemical stains as a diagnostic adjunct has become a popular tool. Although undoubtedly, immunohistochemistry has its role in the diagnosis of difficult cases, to date there are no specific markers that would distinguish thymic epithelial neoplasms from other tumors and interpretation of immunohistochemical results should only ever be made in conjunction with accurate morphologic analysis and careful clinical evaluation. This article will review the current knowledge of the immunohistochemical phenotype of thymic epithelial neoplasms with particular emphasis on its use for diagnostic purposes and the latest advances in this field.