**3.4 Thymopharyngeal duct cyst**

Thymopharyngeal duct cyst, also known as thymic remnant cyst (TRC), is one of the rare lesions of the thymus gland [26]. A majority of these cysts occur in the first decade of life and on the left side of the neck [27]. These cysts may be completely separated from the normal thymic tissue or attached to the thymus [28]. CT scan shows TRCs as a cyst with thin wall. After administration of contrast, thymic remnant cysts show peripheral rim enhancement [29]. Malformations of the lymphatic system, external laryngocele, lymphadenopathy, vallecular cyst, cystic neuroblastoma, and thyroglossal cyst are among differential diagnoses of TRCs [30]. It is very important to differentiate TRCs with the second branchial cleft anomalies as they require different treatment approaches.
