Mediastinal teratoma with mature fetal pancreatic tissue, nesidioblastosis and focal hyperplasia of neuroendocrine cells. A case report

We present a clinical case of rare and poorly diagnosable mediastinal teratoma containing elements of mature pancreas tissue, nesidioblastosis, and focal hyperplasia of neuroendocrine cells in a somatically healthy 25-year-old male. The main diagnostic difficulties are associated with the asymptomatic clinical course of mediastinal teratomas that are usually incidentally discovered during X-ray for other conditions. The pathology is characterized by pronounced morphological heterogeneity of the tumor; if the morphologist is not sufficiently qualified, this often results in a false-positive conclusion of neuroendocrine carcinoma, which, in turn, leads to an inadequate amount of treatment and a wrong prognosis in the patient. Therefore, for verification of the diagnosis, histological specimens should be examined by experts of institutions experienced in morphological differential diagnosis. In this case, an immunohistochemical study of the tumor for insulin, cytokeratins, and markers of