Tumours and tumour‐like conditions of the thymus other than thymoma; a practical approach

Abstract

Masses within the thymus and mediastinum are frequently biopsied to establish a diagnosis. The specimens sent for histopathological analysis are typically small (needle) biopsy specimens on which the pathologist is challenged to provide a classifying diagnosis. Despite the fact that the pathology of the anterior mediastinum is predominantly centred on the thymus and it thus might be expected that the range of possible diagnoses is limited, the list of disease entities is in fact extensive, encompassing hyperplastic conditions and both benign and malignant neoplasms. In addition to primary thymic epithelial tumours, a number of less common diseases typical for this location may be encountered, including extragonadal germ cell tumours, lymphomas, soft tissue tumours and a number of conditions which may simulate a tumour, such as cysts and inflammatory conditions. In this review, the disease entities that may be encountered in biopsy material from anterior mediastinal/thymic processes are discussed and an approach to tackle the differential diagnosis is provided.

Role of parathymic lymph nodes in metastatic tumor development

“…In addition, other neoplastic diseases typical for this location may be encountered, such as extragonadal germ cell tumors; lymphomas; soft tissue tumors; and conditions that simulate tumor development, cyst formation, and inflammatory conditions [3]. Lymphoma represents a common malignancy to selectively target this nodal chain, which usually results in the contiguous spread from the anterior mediastinal or paratracheal area to other mediastinal lymph node groups [4].…”

Cystic Lesions of the Mediastinum

“…Thymic tissue must be present at least focally within the wall of the cyst. They are rarely inflamed and usually asymptomatic and incidentally detected [7]. Acquired thymic cysts are almost always multilocular with wall thickening secondary to inflammatory infiltrate.…”

“…Acquired thymic cysts are almost always multilocular with wall thickening secondary to inflammatory infiltrate. They have been associated with prior thoracotomy or radiation therapy and a variety of inflammatory/infectious or neoplastic processes including but not limited to myasthenia gravis, thymoma, systemic lupus erythematosus, Sjogren's syndrome and HIV infection [7].…”

Immunohistochemical differentiation of metastatic tumours

“…10 Although cytogenetic abnormality i(12p) is shared by the majority of gonadal and extragonadal germ cell tumours and related secondary somatic malignant tumours, there is no "pan-germ cell tumour" immunohistochemistry marker available. It is important to recognize germ cell tumours since they are highly sensitive to cisplatinumbased chemotherapy even at an advanced stage.…”