Non-neoplastic/Inflammatory Lesions in the Mediastinum

Abstract

Main non-neoplastic/inflammatory lesions subjected to mediastinal biopsies include fibrosing (sclerosing) mediastinitis, thymic hyperplasia, various cysts, normal or abnormal ectopic tissues within the mediastinum. Increasingly, limited approaches such as core needle and fine needle aspiration biopsies have been used in lieu of surgical biopsies in the evaluation of mediastinal pathology. However, it is extremely difficult to reach a definite diagnosis of non-neoplastic/inflammatory mediastinal lesions based on small biopsies and cytology specimens partly due to the nonspecific nature of their findings typically seen in those specimens. Oftentimes, the histopathologic features in these non-neoplastic conditions may overlap with those of various neoplastic diseases such as Hodgkin and non-Hodgkin lymphomas, thymic tumors, and germ cell tumors. Also, one should consider a sampling issue; in any given biopsy, it is important to question whether the observed findings account for the real lesion or simply represent a nonspecific reactive change at the periphery of the targeted lesion that is missed. Thus, the importance of careful clinical and radiologic correlation is paramount and a re-biopsy should be considered whenever there is a significant gap between the clinical and pathologic findings. In this chapter, salient features of the main non-neoplastic/inflammatory mediastinal lesions are discussed including a newly described IgG4-related disease involving the mediastinum as fibrosing mediastinitis. A better understanding of the protean clinical and histopathologic manifestations of these conditions should aid in the interpretation of small mediastinal biopsies.