Rhabdomyomatous Carcinoma of the Thymus

Chromophobe-like carcinoma of the thymus: A clinicopathological and immunohistochemical correlation of 5 cases

Five cases of primary thymic carcinoma with distinct histopathological features resembling chromophobe carcinomas are presented. The patients were four men and one woman ranging in age between 43 and 72 years. Clinically, the patients presented with non-specific symptoms of dyspnea and chest pain. Diagnostic imaging revealed the presence of anterior mediastinal masses. All patients underwent complete surgical resection of their tumors via thoracotomy. Grossly, the tumors measured between 4.0 and 5.5 cm in greatest diameter and were ill-defined neoplasms with infiltrative borders; they were light brown in color and had a lobulated surface. Areas of hemorrhage and necrosis were not identified. Histologically, all tumors shared similar histopathological features, mainly the presence of infiltrative tumor islands separated by a fibrocollagenous stroma. At higher magnification, the neoplastic cellular proliferation was composed of medium-sized, round to polygonal cells with eosinophilic or granular cytoplasm and a clear perinuclear cytoplasmic halo, which imparted a chromophobe-like appearance. Nuclear atypia and mitotic activity were identified. Histochemical stains for colloidal iron were negative while immunohistochemical stains for pancytokeratin, cytokeratin 5/6, and p40 were positive in all cases, supporting squamous differentiation in these tumors. Clinical follow-up information was obtained in three patients all of whom died between 3 and 5 years after initial diagnosis, while two patients were lost to follow-up. The cellular characteristics of these tumors represent an unusual variant of thymic carcinoma that may pose a diagnostic challenge in small biopsies and that could be easily confused with other primary or metastatic tumors.

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.

Selected Case From the Arkadi M. Rywlin International Pathology Slide Seminar: Atypical Thymoma With Rhabdomyomatous Differentiation

Thymic epithelial neoplasms with foci of rhabdomyomatous differentiation are rare. A case is presented of a primary thymic epithelial neoplasm showing the features of an atypical spindle cell thymoma that contained foci of bland-appearing rhabdomyomatous cells. The histologic and immunohistochemical features of this tumor are discussed along with a review of the literature and the comments from the AMR members to the case.

Mesenchymal tumours of the mediastinum--part II

This is the second part of a two-part review on soft tissue tumours which may be encountered in the mediastinum. This review is based on the 2013 WHO classification of soft tissue tumours and the 2015 WHO classification of tumours of the lung, pleura, thymus and heart and provides an updated overview of mesenchymal tumours that have been reported in the mediastinum.

Lipomatous tumors of the anterior mediastinum with muscle differentiation: a clinicopathological and immunohistochemical study of three cases

Three cases of primary lipomatous tumors of the anterior mediastinum with prominent muscle differentiation are presented. The patients were two women and one man between the age of 52 and 68 years. All patients presented with progressive shortness of breath. Radiographically, all patients demonstrated anterior mediastinal tumors which were surgically resected. In two cases, the gross findings were those of circumscribed tumors, while one lesion was described as an ill-defined and unencapsulated neoplasm. Histologically, two cases corresponded to a well-differentiated liposarcoma, while the third was a thymolipoma. Extensive areas of smooth muscle were identified in one of the liposarcomas, while the other contained areas of mature skeletal muscle. The thymolipoma displayed a prominent myoid component. Immunohistochemical studies for muscle markers including smooth muscle actin, desmin, and myoglobin showed positive staining in the corresponding components. Follow-up information showed that one patient with liposarcoma died 60 months after initial diagnosis, while the other two patients remain alive and well 16 and 36 months after diagnosis, respectively. The current cases highlight the spectrum of muscle differentiation that can be seen in adipose tumors of the anterior mediastinum and also emphasize the difficulty that such a diagnosis can pose when confronted with limited mediastinoscopic biopsies.

A rhabdomyoma within a multilocular thymic cyst in a p53-null mouse

A 9-month-old p53-null female mouse was found dead in its cage. At necropsy, a large thymic mass encompassed the heart. Microscopically, the mass was composed of numerous varying-sized cysts lined with simple squamous epithelial cells to columnar ciliated cells. Also present within this mass was a large aggregate of loosely arranged fusiform-shaped cells. These cells also were found in smaller numbers in the connective tissue surrounding the cysts. The larger aggregate of fusiform cells was positive for desmin and S-100 and negative for smooth muscle actin. Electron microscopy revealed well-formed Z lines and I bands of skeletal muscle phenotype. A diagnosis of rhabdomyoma within a congenital multilocular thymic cyst was made. The thymus contains a small population of myoid cells, which should be taken in consideration when evaluating thymic tumors.

Thymic carcinoma: update of current diagnostic criteria and histologic types

Thymic carcinomas are rare tumors thought to derive from thymic epithelium. Because of the complex embryological origin of the thymus, whose development includes contributions from the third and, to a lesser extent, the fourth pharyngeal pouches, thymic carcinomas are endowed with great morphologic heterogeneity. A large number of histologic types have been described that resemble tumors arising in other organs. Unfortunately, no definitive pathognomonic histological features or immunohistochemical markers are associated with these tumors, making them a real challenge for diagnosis. Because of their close similarity with tumors arising at other organs, the diagnosis of thymic carcinoma must be regarded, for the most part, as a diagnosis of exclusion. This review will focus on current criteria for diagnosis of these tumors, with a review of the various histopathologic appearances that they can adopt.

Mediastinal rhabdomyoma: case report and review of the literature

Rhabdomyomas are benign tumors in which at least some cells are differentiated as skeletal muscle cells with cytoplasmic cross-striations. Extracardiac adult rhabdomyoma is an extremely uncommon benign neoplasm that usually involves the head and neck region. Rare cases have been reported to involve other sites of the body including mediastinum. We report the fourth case of mediastinal adult rhabdomyoma.