Ectopic Cervical Thymus in Adult: An Incidental Finding

Thymus is a paired organ which develops during the sixth week of fetal life, attains maximum size by three years and involutes in adult life. Anatomically it is situated in superior mediastinum. Thymus can be present at ectopic sites like neck, skull base, middle ear, submandibular gland and tonsil. Ectopic Cervical Thymus (ECT) is very rare in adults and can present as a solid mass, cyst or thymoma. ECT occurs due to failure of descent during embryonic development. ECT can mimic any pathologic mass, metastatic deposit or lymph node enlargement. We report a case of ECT discovered incidentally in an adult during histopathological examination of thyroid carcinoma. In addition, we described the role of immunohistochemistry markers to confirm the various thymic components.