Cervical thymic cysts: CT appearance of two cases including a persistent thymopharyngeal duct cyst

Abstract

The differential diagnosis of cervical cysts in children includes common entities such as branchial cleft cysts, thyroglossal duct cysts, and cystic hygromas. Congenital thymic cysts are uncommon and often misdiagnosed as either branchial cleft cysts or cystic hygromas. However, they may have an appearance on CT that can be characteristic. The course of the descent of embryologic thymic tissue in the neck to the mediastinum indicates the potential site of deposition of an ectopic cervical thymic cyst. In a child, a cystic lesion that has an intimate relationship to the carotid sheath is likely to be a thymic cyst. Of the approximately 100 cases of vestigial cervical thymus or thymic cysts that have been reported in children, only 5 cases of a persistent thymopharyngeal duct cyst have been described [1-5]. In two of these five, the persistent thymopharyngeal duct cyst was demonstrated by CT [1,2]. We report one additional case of a cervical thymic cyst and one case of a persistent thymopharyngeal duct cyst both depicted by CT.

Cervical thymic cysts

“…Masses derived from the third pharyngeal pouch are usually adherent to the carotid sheath and pass downward laterally to the thyroid capsule and along the anterior border of the sternocleidomastoid muscle to the manubrium. A fourth pharyngeal pouch tract extends from the apex of the pyriform sinus inferiorly to the superior laryngeal nerve, externally to the recurrent laryngeal nerve and pass inferiorly along the trachea to eventually swing forward between the arch of the aorta and the subclavian artery [17,18]. This anatomical understanding is important in order to correctly diagnose an ectopic thymic cyst; almost all are unilateral and most commonly on the left side of the neck [19].…”

“…Subsequently, the development of the mass can either be sudden, due to infection or haemorrhage, or slowly progressive. Only 6-10% of the patients complain about dysphagia, dyspnea, stridor, cervical pain or hoarseness and vocal cord paralysis [18,19,26,27]. In general, ectopic thymic tissue appears to invoke symptoms relatively more commonly in children than in older patients with over 50% of cases involving children experiencing respiratory and feeding difficulties [28].…”

Thymopharyngeal Duct Cyst: A Case Presentation and Literature Review

“…However, in the ten cases reviewed, five cases were right-sided masses and at least three were female. 1,2,3,5,6,7,12 There can be associated findings of hoarseness, dysphagia, and stridor, especially in neonates. 5 Often, the cyst will appear and gradually enlarge following an indolent, painless course.…”

“…6 A tract develops beginning near the piriform sinus, extending through the thyrohyoid membrane, descending between the carotid artery and vagus nerve postero-inferiorly to the glossopharyngeal nerve, lateral to the thyroid lobe, and ending at the manubrium. 1,2,8 The embryologic development of the thymopharyngeal duct, as a result of its well defined anatomic relationships, aids in the diagnosis of cystic masses that follow a similar course.A thymopharyngeal duct cyst is an uncommon diagnosis and so its clinical presentation, much like any other analyzed aspect of this disease process, suffers from a small sample size. In the literature to date, there are ten reported cases in children.…”

Thymus

“…About five cases have been described in the literature (Burton et al 1995). About five cases have been described in the literature (Burton et al 1995).…”