Background: Incidences of ectopic thymic tissue in the neck have been reported in various conditions. Despite their diversity, there are only a few studies focusing on patients without any thymic disease. The goal of this study was to detect the frequency of ectopic thymic tissue in the necks of adult patients without any thymic disease.
Material/Methods: Ninety patients with thyroid disorder who were candidated for thyroidectomy were selected. Five specimens were taken from each patient, including two biopsies before thyroidectomy from the right and left thyrothymic ligament just near the thyroid. The other specimens were taken after thyroidectomy: two from right and left carotid sheet at the base of the neck and the fifth from the adipose tissue just above the fourth tracheal cartilage. The specimens were stained with H&E and cytokeratin antibody to detect thymic tissue.
Results: Ectopic thymic tissue was found in four cases (4.45%), one by H&E and the others by immunohistochemical staining.
Conclusions: In patients with myasthenia gravis, hyperplasia of thymic tissue occurs in their thymus gland and ectopic thymic tissue as well. As a result, the probability of finding ectopic thymic tissue in such a patient is higher than in patients without any thymic disease. Also, removing of this tissue can improve the outcome of patients.

Keywords: Thymus Gland - pathology, Neck - pathology, Iran - epidemiology, Choristoma - pathology, Biopsy, Thymus Gland - pathology, Neck - pathology, Iran - epidemiology, Choristoma - pathology, Biopsy