Background:Different approaches to treat myasthenia gravis showed variable outcomes probably because of remained ectopic thymic tissue. The aim of this study is to determine incidence of thymic tissue in cases without any thymic disease.Materials and Methods:Seventy-two patients scheduled for open heart surgery during 2000 and 2007 without thymic disease that were enrolled in the study at Chamran Hospital. Intraoperative biopsies were taken form aortopulmonary window, aortocaval groove and left and right pericardiophrenic regions. Finally, the distribution of ectopic thymic tissue was evaluated in above regions.Results:Thymic tissue was found overall in 70.85% of patients. The most common sites for thymic tissue were left pericardiophrenic (50%) and right pericardiophrenic (31.9%) regions. Frequencies of ectopic thymus in aortopulmonary window and aortocaval groove were 19.4% and 12.5%, respectively.Conclusion:Because of high incidence of ectopic thymic tissue in mediastinum in patients without thymic disease, we recommend wide excision of thymus gland and all of adipose tissue in patients with myasthenia gravis.

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