Benign Hematopoietic Disorders of the Mediastinum

Benign or reactive hematopoietic lesions of the mediastinum represent a large part of the routine cases of surgical pathologists and thoracic pathologists. Most of these lesions present as mediastinal lymphadenopathy with or without disease elsewhere, and the main clinical and radiologic suspicion is that of malignancy. A biopsy is obtained in an attempt to establish a diagnosis. In some cases, benign lesions of the mediastinum may be the main pathology, whereas in other cases a benign or reactive condition may be an incidental finding seen in biopsies obtained for other reasons (staging for lung adenocarcinoma, rule out metastatic disease, etc.). Benign or reactive conditions of the mediastinum discussed here include granulomatous lymphadenitis, Castleman disease (unicentric and multicentric types), sclerosing mediastinitis/IgG4-related disease, and histiocytic disorders. For most of these, morphology and a limited panel of ancillary studies are helpful, but for others, clinico-radiologic correlation is mandatory to be able to render an appropriate pathologic interpretation.