The Child With a Neck Mass

Bernadette L. Koch, MD

Disclosures

Appl Radiol. 2005;34(8):8-22. 

In This Article

Cystic Neck Masses

The majority of cystic neck masses in children are congenital malformations and include thyroglossal duct cysts, branchial apparatus cysts, dermoid cysts, and lymphatic malformations.

The thyroglossal duct (TGD) is a normal fetal structure that extends from the foramen cecum at the posterior aspect of the tongue to the lower neck in the region of the thyroid bed. The TGD normally involutes during the 5th or 6th week of fetal life. If any portion of the duct does not involute, remnant secretory epithelium may form a cyst.[6,7] Most TGD cysts occur in the midline. Twenty percent to 25% are in the suprahyoid neck, 15% to 59% are at the hyoid bone, and 25% to 65% are in the infrahyoid neck.[7,8] Patients typically present with a midline neck mass that elevates with swallowing or protrusion of the tongue. If infected, they might present with warmth, erythema, and fever. In the past, nuclear medicine imaging with Tc-99m-pertechnetate was used to assess for the presence of a bi-lobed thyroid gland in the lower neck and rule out ectopic thyroid in the midline mass. More recently, US has been used to evaluate for a normal-appearing bi-lobed thyroid gland in the lower neck and to confirm the cystic nature of the midline neck mass.[1] Uncomplicated thyroglossal duct cysts may be anechoic, hyperechoic, or heterogeneous on US. The presence of intralesional echoes does not imply superimposed infection or hemorrhage (Figure 1).[9] On CT and MRI, thyroglossal duct cysts will appear as fluid-filled cysts of variable attenuation and signal intensity, depending on the protein content of the cyst (Figure 2). If there is superimposed infection, there may be edema in the adjacent soft tissues and peripheral contrast enhancement. Treatment of thyroglossal duct cysts is surgical excision (Sistrunk procedure) that includes excision of the cyst, the entire remnant tract, and a central portion of the hyoid bone.[10]

Thyroglossal duct cyst. (A) Transverse sonographic image shows a hypoechoic well-defined paramidline neck mass with a thin imperceptible wall and increased through-transmission. (B) Transverse sonographic image in the lower neck shows a normal-appearing bilobed thyroid gland.

Thyroglossal duct cyst. (A) Transverse sonographic image shows a hypoechoic well-defined paramidline neck mass with a thin imperceptible wall and increased through-transmission. (B) Transverse sonographic image in the lower neck shows a normal-appearing bilobed thyroid gland.

Thyroglossal duct cyst. Axial CT image shows a low-attenuation nonenhancing midline mass at the base of the tongue.

Normal branchial apparatus embryology is quite complex and beyond the scope of this manuscript. However, in general, the branchial apparatus structures develop between the 4th and 6th week of gestation and consist of 6 pairs of mesodermal branchial arches separated by 5 paired endodermal pharyngeal pouches internally and 5 paired ectodermal bran-chial clefts externally. Anomalies of the branchial apparatus may be in the form of cysts, sinus tracts, or fistulae. Branchial apparatus cysts are the most common branchial apparatus anomalies that require imaging.

First branchial anomalies account for only 8% of all branchial anomalies and are usually cysts or sinuses near the external auditory canal, the pinnae, or the region of the parotid gland (Figure 3).[11,12,13] Patients typically present with masses or sinus tracts, with or without recurrent infection. The cysts may be imaged with CT, US, or MRI. MR imaging is ideal in evaluating the fluid-filled tract, which may extend from the more superficial cyst to the external auditory canal (Figure 4).

Diagram of the face shows distribution of first branchial apparatus anomalies (Figure reprinted with permission from Olsen KD, Maragos NE, Weiland LH. First branchial cleft anomalies. Laryngoscope. 1980;90:423-43611; and from Benson MT, Dalen K, Mancuso AA. Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. RadioGraphics. 1992;12:943.12)

First branchial apparatus anomaly. Axial fast spin-echo images (A) at the level of the parotid gland and (B) at the level of the lower aspect of the external auditory canal show two hyperintense cystic masses that were connected by a small fluid-filled tract (images of the tract not included).

First branchial apparatus anomaly. Axial fast spin-echo images (A) at the level of the parotid gland and (B) at the level of the lower aspect of the external auditory canal show two hyperintense cystic masses that were connected by a small fluid-filled tract (images of the tract not included).

Second branchial apparatus cysts are the most common and account for up to 95% of all branchial apparatus anomalies. Most are located anterior to the sternocleidomastoid muscle, posterior to the submandibular gland and lateral to the carotid sheath (Figure 5). Occasionally, cysts may protrude between the internal and external carotid arteries; rarely, they are deep to the platysma muscle and anterior to the sternocleidomastoid muscle or located directly adjacent to the pharyngeal wall.[14] As with other cysts, these lesions will be hyperechoic or anechoic on US, low in attenuation on CT, and fluid in signal intensity on MRI unless there is associated superimposed infection, which will change the imaging characteristics on all modalities. The key to making this diagnosis is the location of the lesion.

Second branchial apparatus cyst. Axial postcontrast CT image shows a well-defined, low-attenuation, nonenhancing left neck mass anterior to the sternocleidomastoid muscle, lateral to the carotid sheath, and posterior to the submandibular gland.

The most common third branchial apparatus anomaly is the thymic cyst. These are rare remnants of the third branchial pouch. In normal embryologic development, the thymic primordia migrates from the pharynx caudally and fuses in the anterior mediastinum along the course of the thymopharyngeal duct. Similar to the thyroglossal duct cysts, when the duct fails to involute, a cyst may occur anywhere along the thymopharyngeal duct from the angle of the mandible to the upper mediastinum (Figure 6).[12,15]There may be intralesional echoes on US with or without superimposed hemorrhage or infection. Up to 50% of cervical thymic cysts will be continuous with the mediastinal thymus (Figure 7).[16] Cervical thymic cysts are intimately associated with the carotid sheath; they frequently splay the carotid artery and jugular vein, particularly when they involve the suprahyoid neck. As with other branchial apparatus anomalies, the location is the key to suggesting the diagnosis. In a child, any cystic mass that involves the neck and also extends to the anterior mediastinum should certainly suggest a cervical thymic cyst.

Diagram shows the course of the thymopharyngeal duct. (Figure reprinted with permission from Benson MT, Dalen K, Mancuso AA. Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. RadioGraphics. 1992;12:94312; and from Zarbo RJ, McClatchey KD, Areen RG, et al. Thymopharyngeal duct cyst: A form of cervical thymus. Ann Otol Rhinol Laryngol. 1983;92(3 Pt 1):284-289.15 )

Third branchial apparatus anomaly -- thymic cyst. (A) Axial postcontrast CT image at the level of the hyoid bone shows a well-defined, lowattenuation, nonenhancing mass in the region of the carotid sheath deviating the internal carotid artery anteriorly (arrow) and the jugular vein laterally (arrowhead). (B) Axial postcontrast CT image at the level of the upper mediastinum shows extension of the low-attenuation mass to the expected level of the thymus.

Third branchial apparatus anomaly -- thymic cyst. (A) Axial postcontrast CT image at the level of the hyoid bone shows a well-defined, lowattenuation, nonenhancing mass in the region of the carotid sheath deviating the internal carotid artery anteriorly (arrow) and the jugular vein laterally (arrowhead). (B) Axial postcontrast CT image at the level of the upper mediastinum shows extension of the low-attenuation mass to the expected level of the thymus.

Dermoid cysts may contain squamous epithelium and skin appendages such as hair follicles and sebaceous glands. Epidermoid cysts contain only squamous epithelium. Both may present as midline neck masses with variable attenuation, echogenicity, and signal intensity, depending on internal contents (Figure 8). If fat globules are identifiable on CT or MRI, then a dermoid cyst is the most likely diagnosis. If there are associated calcifications, then the lesion is more likely a teratoma or venous malformation. If the lesion is entirely composed of fat, then simple lipoma is the most likely diagnosis (Figure 9).

Dermoid cyst. Axial postcontrast CT image shows a low-attenuation, nonenhancing right paramidline anterior neck mass deep to the strap muscles. Differential diagnosis includes a thyroglossal duct cyst.

Lipoma. Axial postcontrast CT of the lower neck shows a lobulated fat-attenuation mass at the cervicothoracic junction.

Lymphatic malformations (LMs) are vascular malformations composed of primative embryonic lymph sacs of varying sizes. Lymphatic malformations typically increase in size as the child grows, and they may show rapid increase in size in association with upper respiratory tract infection or intralesional hemorrhage. Although they may be seen in genetic syndromes such as Turner's syndrome, Noonan's syndrome, and trisomy 21 syndrome, most LMs occur in children with normal karyotype.

Lymphatic malformations can be divided into microcystic, macrocystic, or mixed lesions. They may be unilocular, multilocular, focal, or diffuse/infiltrative. The fluid-filled spaces are usually anechoic or hypoechoic on US and usually have low attenuation on CT and fluid signal intensity on MRI. There may be minimal enhancement of internal septations.[17,18,19,20] They are the primary cystic malformation to present with transspatial involvement (Figure 10). Of all cystic lesions in the neck, LMs are the most likely to hemorrhage, frequently resulting in intralesional fluid-fluid levels (Figure 11). As with other cystic lesions, if there is superimposed infection, the imaging characteristics will change accordingly.

Lymphatic malformation. Axial postcontrast CT image shows a lowattenuation nonenhancing left supraclavicular neck mass that extends to the posterior paraspinal soft tissues of the upper back.

Lymphatic malformation. Axial fast spin-echo image of the neck shows a multilocular right neck mass deep to the sternocleidomastoid muscle with several fluid-fluid levels consistent with blood products secondary to prior intralesional hemorrhage.

Lymphatic malformations are frequently part of mixed vascular malformations, with the most common additional component being a venous malformation. The venous malformation component may appear as a cystic malformation on precontrast images but will show postcontrast enhancement and may contain phleboliths (Figure 12). When LMs are complex and transspatial or when they involve multiple structures of the neck (eg, airway, tongue, floor of mouth) or the parotid gland, and in patients with combined vascular malformations, MR imaging is the preferred modality.[18,19,20]

Mixed lymphatic and venous malformation. Postcontrast axial CT images show an enlarged right palatine tonsil without significant contrast enhancement, with multiple intralesional small round calcifications consistent with phleboliths.

The preferred treatment of LMs is surgical excision. However, complete surgical excision may be difficult when the lesions are microcystic and infiltrative. Macrocystic lesions may also be treated with percutaneous sclerotherapy, including alcohol solution, cyclophosphamide, bleomycin and doxycycline.[21,22,23]

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