RESUMO
Introduction: IgG4-related disease is now considered to result from an imbalance in the regulatory immune system, and it is diagnosed on the basis of clinical and histopathologic evidence such as the presence of lymphoplasmacytic infiltrates, especially increased IgG4-positive plasma cells and fibrotic sclerosing tissue. Case report: We report herein a 45-year-old male patient with mediastinal mass with IgG4-related disease. IgG4-related disease can involve any organ but the most frequently involved sites include pancreato-hepatobiliary tract, salivary glands, and kidneys, generally manifesting as a mass in one or more sites mimicking a neoplasia. In the thoracic region, IgG4-related disease manifests as interstitial lung disease and fibrosing mediastinitis. Mediastinal lesion in our patient was quite resemble to mediastinal tumor derived from anterior mediastinum. This is the first case with mediastinal mass in a patient with this disease. Conclusion: Although very rare, we should rule out this disease as differential diagnosis in patients with anterior homogeneous density mediastinal mass simulating mediastinal tumor.