Mediastinal Nodular Lesions Synchronous to Lung Carcinoma on Frozen Section: Trap and Lesson

Thymoma is the most frequent neoplasm arising in the anterior mediastum. It usually presents as an enlarged central mass. In the literature, multiple thymoma is described as an unusual finding; rare variants have also been described, like the signet ring-like cell variant. Evidence of co-existence of signet ring-like cells and lymphocytes in small biopsies from nodular mediastinal lesions can lead to a diagnosis of metastatic carcinoma, mostly at frozen sections. Thymoma and pulmonary carcinoma are very rarely associated neoplasms. We present a case of two mediastinal lesions discovered during pulmonary carcinoma staging. At frozen section, a diagnosis of 'epithelioid proliferation associated to lymphoid tissue' was advanced on a sample of nodular lesions and of 'carcinoma' on pulmonary biopsy. Double AB Type Thymoma with a signet ring cell-like component, synchronous to pulmonary adenocarcinoma, was the diagnosis made on formalin fixed-paraffin embedded samples. Reporting the coexistence of these two entities can help pathologists and surgeons to establish the best management of similar patients.