Reactive, Developmental, Inflammatory, and Tumorlike Conditions

Abstract

A variety of reactive, developmental, inflammatory, and tumorlike conditions can occur in the mediastinum (Table 1.1). Congenital and developmental cysts can present as a mass lesion in the mediastinum and may occur in a variety of settings. Congenital cysts usually occur in younger patients and are unilocular and small; they can arise anywhere along the anatomic course of embryonic descent of the thymus, including the neck. Developmental cysts can arise from displaced or ectopic remnants, such as foregut cysts and enteric duplication cysts. Acquired cysts can arise as a result of underlying inflammatory processes and can grow to be quite large and multiloculated. Thymic hyperplasia is another reactive process that presents as enlargement of the thymus and clinically can simulate a malignancy. Inflammatory conditions affecting the mediastinum include acute and chronic inflammation (mediastinitis), granulomatous processes related to sarcoidosis (affecting primarily mediastinal lymph nodes) or fungal infection, and end-stage fibrosing inflammation resulting in idiopathic sclerosing mediastinitis. Other developmental abnormalities that occur with some frequency in the mediastinum are the presence of ectopic thyroid or parathyroid tissue, which may give rise to tumor growths secondary to hyperplasia, benign nodules, or development of malignancy. Finally, a variety of benign tumorlike conditions in this anatomic compartment can lead to tumor masses that may be confused with malignancy, including thymolipoma, thymofibrolipoma, and Castleman’s disease.