Cervical Ectopic Thymus

TE Herman and MJ Siegel Department of Radiology, Mallinckrodt Institute of Radiology, St Louis Children’s Hospital, Washington University School of Medicine, MO, USA

Journal of Perinatology (2009) 29, 173–174; doi:10.1038/jp.2008.89 to the carotid sheath, extending anterolaterally to it. Thymopharyngeal cysts also maintain close relationship with the carotid sheath. Cervical ectopic thymus occurs primarily in males (85% of Cases presentation patients) and is slightly more common on the right than the left A full-term infant boy was found to have a palpable left neck mass (56%).1 Most patients are asymptomatic, although hoarseness, at birth. The patient was asymptomatic without stridor, swallowing dysphagia and stridor have been reported.2 The lesions have a difﬁculty or hoarse cry. The mass was evaluated initially with a characteristic MRI and sonographic appearance. They are neck magnetic resonance imaging (MRI) scan (Figure 1), and homogeneous masses which are isointense to muscle on subsequently with a neck sonogram (Figure 2). The MRI scan T1-weighted sequence and hyperintense on T2-weighted demonstrated a 3.0 Â 2.4 Â 2.7 cm homogenous soft tissue mass. sequences.3 On sonography, the lesions are hypoechoic with The mass was isointense to muscle on T1-weighted images, and hyperintense to muscle on T2-weighted images. The mass extended from the anterolateral border of the sternocleidomastoid where it was intimately related to the left carotid artery. The infant was not given contrast for the MRI study. The sonogram demonstrated a hypoechoic mass, with linear hypoechoic foci throughout and good vascularity on the Doppler images, lying anterolateral to the sternocleidomastoid muscle.

Denouement and discussion The patient had cervical dissection with resection of the mass with monitoring of the facial nerve. The histological examination of the removed mass demonstrated ectopic hyperplastic cervical thymus. Ectopic cervical thymus is because of the failure of descent of the thymus, which arises from the third and partially from the fourth pharyngeal pouches at the level that will become the piriform sinus. The third pharyngeal pouch also gives rise to the inferior parathyroid glands.1 Beginning in the sixth week of fetal life, the thymic precursor begins its descent to the mediastinum along the thymopharyngeal duct.2 This duct is in close relationship to the carotid sheath. Failure of complete descent will result in a cervical ectopic thymus. Small residual of the thymopharyngeal duct may result in a thymopharyngeal cyst. Cervical ectopic thymus, thus, will have a close relationship Figure 1 (a) Coronal T1-weighted image through mass, (b) coronal T2-weighted image at the same level. (c) Axial T-2 weighted image at the level of Correspondence: Dr TE Herman, Department of Radiology, Mallinckrodt Institute of the glottis, (d) axial T-2 weighted image at the level of the subglottic trachea. Radiology, St Louis Children’s Hospital, Washington University School of Medicine, A left cervical mass (M) is seen lying anterior to the carotid artery (arrow) and 510 South Kingshighway Blvd., St Louis, MO, 63110, USA. extending anterolaterally to the sternocleidomastoid muscle. The mass is isodense E-mail: [email protected] to muscle on T1-weighted sequences and bright on T2-weighted images. It has Received 29 April 2008; accepted 13 May 2008 an intimate relationship to the left internal carotid artery medially. Cervical ectopic thymus TE Herman and MJ Siegel 174

characteristic linear echogenic foci. The mass occurs along the path of the thymopharyngeal duct.4 If the characteristic appearance and location of the mass are recognized, resection and needle biopsy may be avoided.1 Ectopic cervical thymus and thymopharyngeal cyst are uncommon etiologies of congenital neck masses, comprising only approximately 2%, in one series.2 More common masses include branchial cleft cyst, dermoid cyst, hemangioma and lymphangiomas, most of which are predominantly cystic. Branchial cleft cyst is anterolateral to the jugular along the anterior border of the sternocleidomastoid. Lymphangiomas are usually in the posterior triangle of the neck. Solid masses are more uncommon but include rhabdomyosarcoma, lymphoma and neuroblastoma. The homogeneous appearance on MRI along with the characteristic location paralleling the carotid sheath should help to differentiate ectopic thymus from these malignant masses. However, if there is a concern, resection or biopsy may be undertaken.

References 1 Zielke AM, Swischuk LE, Hernandez JA. Ectopic cervical thymic tissue: can imaging obviate biopsy and surgical removal. Pediatr Radiol 2007; 37: 1174–1177. 2 Kaufman MR, Smith S, Rothschild MA, Som P. Thymopharyngeal duct cyst. Figure 2 (a) Transverse and (b) longitudinal sonographic images of the cervical Arch Otolaryngol Head Neck Surg 2001; 127: 1357–1360. mass (M) at the level of the sternocleidomastoid (SCM) muscle. (c) Longitudinal 3 Liu D, Katajima M, Awai K, Nakayama Y, Tamura Y, Suda H et al. Ectopic cervical image through mass with color-Doppler imaging. The mass is well deﬁned, lies thymus in an infant. Radiat Med 2006; 24: 452–455. anterior to the carotid artery (arrow) and has an echogenicity equal to the SCM 4 DeFoer B, Vercruysse JP, Marien P, Colpaert C, Pilet B, Pouillon M et al. Cervical muscle and less than that of adjacent fat. Thin echogenic linear densities are ectopic thymus presenting as a painless neck mass in a child. J Belg Rad 2007; 90: typical of normal thymus. The mass is vascular on color-Doppler imaging. 281–283.

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