Applied Radiology

Dr. Kan is a Diagnostic Radiology resident at the University of Chicago Hospitals, Chicago, IL.

Congenital pediatric neck masses can be classified based on location and radiographic characteristics. In general, thyroglossal duct cysts, branchial cleft cysts, ranulas, lymphatic malformations, and dermoids tend to be cystic in nature; while hemangiomas, teratomas, and fibromatosis colli have heterogeneous morphology with solid and possible cystic components.

Teratomas and hemangiomas present anywhere within the neck. Fibromatosis colli is a solid mass exclusively found within the sternocleidomastoid muscle.

Thyroglossal duct cysts and dermoids are usually located anterior and midline or paramedian within the anterior cervical triangle. Branchial cleft cysts and ranulas are also found in the anterior cervical triangle but are more lateral in location than thyroglossal duct cysts. Lymphatic malformations are usually found in the posterior cervical triangle.

This article will classify congenital neck masses on the basis of radiographic characteristics and will review presentation, embryology, imaging characteristics, and management.

Cystic neck masses

Thyroglossal duct cyst

For all etiologies for childhood neck masses, the incidence of thyroglossal duct cysts is second only to infectious lymphadenopathy. ¹ Among the congenital neck masses, they are the most common (70%). ²

This disorder is the result of abnormal migration of the embryologic thyroid tissue from the foramen cecum located at the base of the tongue to its expected midanterior neck location. ³ It usually presents as an asymptomatic or an infected midline or paramedian neck mass that moves cephalad with swallowing or tongue extension. Thyroglossal duct cysts present as a simple cyst with an associated connecting duct that can be demonstrated by either computed tomography (CT) or ultrasound (US) (figures 1 and 2). If infected, the US and CT presentations are variable. US may show punctate echogenities representing infectious debris within the lesion and potential irregular and unsharp posterior shadowing that represents subcutaneous emphysema (figure 3). The internal structure of the infected cyst may become complex with fluid-fluid levels, septations, and a thickened wall, which can represent hemorrhage, pus, and scarring. A loss of normal soft tissue planes, as well as subcutaneous fat stranding, is visible on CT.

Preoperative neck US and/or Tc-99m pertechnetate imaging is recommended to evaluate the thyroid gland, possible ectopic thyroid tissue, and additional cysts along the location of the thyroglossal duct tract. Approximately 80% of thyroglossal duct cysts are located at or slightly below the level of the hyoid bone. ² To prevent possible future development of ectopic papillary thyroid carcinoma and a nidus for neck infections, surgical removal includes complete excision of the cyst, associated duct, the core of the tongue base, the central hyoid body, as well as possible intra-ductal thyroid tissue. ^1,4 Although rare, squamous cell carcinoma developing within the thyroglossal duct cyst has also been reported. ⁵

Branchial cleft cysts

Branchial cleft cysts result from maldevelopment of the embryonic branchial arches. Branchial clefts are the external interposed spaces with respect to the embryonic branchial arches. There are initially four clefts. Normally, the second through fourth clefts are rudimentary and are absorbed by the adjacent branchial arches. The first branchial cleft eventually develops into the external auditory meatus. ³

Seconds are the most common, and first branchial cleft cysts are the next most frequent. Third and fourth branchial cleft cysts are rare. ²

First branchial cleft cysts are identified clinically in the preauricular region with or without an external sinus tract. ⁶ Since the first branchial cleft normally leads to development of the external auditory meatus, predictable anomalies may be seen in the external auditory meatus, eustacian tube, tympanic cavity, and mastoid air cells. Other associated lesions include middle ear ossicle maldevelopment leading to sensori-neural hearing loss. Aural atresia, cleft palate, and microtia can also occur. ⁷ Conditions to consider when microtia is seen include, but are not limited to, Treacher-Collins syndrome, Goldenhar's syndrome, and branchial-oto-renal syndrome. ⁸

Second branchial cleft cysts are usually located along the anterior border of the sternocleidomastoid muscle within the lateral aspect of the anterior cervical triangle. ¹ These cysts may have a deep or external fistulous tract. The associated structural anomalies predictably are associated with second and third branchial arch structure maldevelopment, which includes the palatine tonsils, tonsillar fossa, and the hyoid bone. ³

US and CT are both helpful for delineation of the cyst and fistulous tracts. When infected, proteinacous debri, hemorrhage, wall thickening of the cyst, and loss of the normal soft tissue planes can be demonstrated by CT or US (figures 4 and 5). Only complete excision of both the cyst and sinus tract secures effective treatment and prevents recurrence. ^6,9,10 Carcinoma can rarely occur from unresected branchial cleft cysts. ¹¹

Ranula

Ranulas are uncommon congenital lesions that present as floor of the mouth masses. They occur secondary to obstruction or an imperforate sublingual salivary, and, less commonly, a submandibular duct, presumably due to traumatic, congenital, or idiopathic obstruction. ^12,13

Usually, ranulas are found in the sublingual space. If they are large, they can present as an anterior cervical triangle mass. If the ranula is not infected or ruptured, they are seen as large simple cystic structures on US. ¹⁴ If they rupture, they tend to extravasate caudally, hence its name of "plunging ranula." Similar findings can be assessed by CT (figure 6).

Ranulas are self-limiting lesions, as they sometimes spontaneously regress or rupture. ¹³ Marsupialization via incision and free drainage into the oral cavity is the preferred treatment. ¹⁵

Lymphatic malformation

The congenital form of cervical lymphatic malformations result from incomplete or lack of drainage of the lymphatic system to the superior vena cava (SVC). In general, these lesions may be categorized according to their size as lymphangioma simplex, cavernous lymphangioma, and cystic hygroma with the latter being the largest one. ¹⁶ Of these three, cystic hygroma is the most common and will be discussed here.

Cystic hygromas usually occur in the posterior cervical triangle and present clinically as a soft, painless mass that can grow slowly with age. ¹⁷ Radiographically, cystic hygromas have a variable presentation. Uncomplicated cystic hygromas will present as a large simple cystic mass by US and CT with or without septations (figure 7). They can sometimes undergo spontaneous or traumatic hemorrhage or become infected, manifesting as a complex, heterogeneously echogenic cystic mass with possible septations. The wall may be thickened with or without adjacent fat stranding by CT or demonstrate poorly defined boundaries of surrounding tissue by US.

Because cystic hygromas may be associated with genetic conditions such as Turner's, Klinefelter's, and Down's syndromes, as well as partial trisomies, screening for concomitant extracervical lesions should be performed. ¹⁷

Prior to surgery, the extent and relationship with the neighboring structures and vascularity of the mass should be assessed. To minimize the chance for recurrence, the mass should be excised completely. Nonsurgical approaches such as intralesional bleomycin injection have results similar to surgical excision. ¹⁸ The lesions generally recur after simple needle aspiration.

Dermoid/epidermoid cysts

Dermoid and epidermoid cysts are rare. When they occur, they are due to entrapment of ectodermal elements underneath the skin. ¹⁹

Epidermoids contain stratified squamous epithelium. Dermoids contain stratified squamous epithelium in addition to skin appendages, which can include sebaceous glands, sweat glands, and hair follicles. When they occur in the neck, they are usually found at the floor of the mouth, similar to ranulas, and less commonly appear as an anterior midline mass that lies over the hyoid bone and can be mistaken for a thyroglossal duct cyst. ¹⁹

Preoperative radiographic evaluation should center on delineation of the cystic margins and assessment of possible occult deep and superficial draining sinuses. ²⁰ By US, dermoid and epidermoid cysts are known to have internal echoes with or without posterior acoustic enhancement. ²¹ The internal echogenicity is expected because they can potentially have secretory, glandular tissue, and keratinous debris. By CT, dermoid and epidermoids are known to variably enhance as well as demonstrate fat and dystrophic calcifications. ¹⁹

Therapy for dermoid and epidermoid cysts is complete excision of the cyst and potential sinus tracts. ²⁰

Mixed neck masses

Vascular anomalies

Congenital vascular anomalies are a result of abnormal endothelial proliferation and are classified into two subcategories: hemangiomas and vascular malformations. ²²

Hemangiomas consist of hyperplastic endothelial cells that grow rapidly in size during the first year of life, but usually regress spontaneously, except in 10% to 20% of cases. ²³ Kassabach-Merritt syndrome is thrombocytopenic coagulopathy in association with large hemangiomas. This syndrome carries a poor prognosis with a 30% to 40% mortality rate. ²⁴

Vascular malformations, unlike hemangiomas, are composed of morphologically normal vascular tissue, which can include arterial, capillary, venous, lymphatic, or a combination of the four tissue types. They do not regress spontaneously but tend to grow proportionately with the child. ²²

By contrast-enhanced CT, both vascular anomalies demonstrate an intense clustering of enhancing vessels (figure 8). By ultrasound, both are usually homogenous and hyperechoic. Hemangiomas demonstrate a high diastolic flow and low resistive index. Vascular malformation Doppler findings are variable and are dependent of the predominant vascular tissue type present.

Management for most hemangiomas is conservative since they usually regress spontaneously. Corticosteroids, interferon, laser, embolization, and surgical excision are potential therapies, if vital structures such as the airway is compromised. ^25-28 Therapy for symptomatic vascular malformations is necessary, however, given that they do not regress spontaneously. Therapy can include embolization, surgical resection, and laser ablation. ²⁸

Teratoma

The neck is the second most common location for teratomas after the sacrum. ²⁹ Neck teratomas have malignant characteristics less frequently than those found in the sacrum. Because of their tendency to increase in size rapidly and their potential adverse location, such as near the airway, work-up and therapy is for prompt complete excision.

On CT, these lesions can have a variable presentation. They can present as large, enhancing, heterogeneous masses with both soft-tissue and cystic components (figure 9). Given the high morbidity and mortality associated with recurrence secondary to incomplete resection, preoperative delineation of tumor extent and relationship with neighboring structures is important. ³⁰

Fibromatosis colli

Fibromatosis colli represents fibrosis and shortening of the sternocleidomastoid muscle that causes torticollis. It is felt to occur secondary to abnormal fetal positioning. Predictably, it is seen in higher frequency in patients who have congenital dysplasia of the hip. ²⁵

Clinically, fibromatosis colli presents in the newborn period with tilting of the head to the affected side of the neck with an associated ipsilateral sternocleidomastoid soft-tissue mass. ¹

By ultrasound, it shows a near homogeneous, predominently hyperechoic mass surrounded on all sides by a thin rim of hypoechoic, normal sternocleidomastoid muscle ³¹ (figure 10). Fine-needle aspiration of the mass is usually performed for diagnosis. ³²

Physical therapy is the first line of treatment. ³³ Surgical transection of the affected sternocleidomastoid muscle is indicated if there is persistent facial hemihypoplasia. ³⁴

Conclusion

In summary, location and radiographic morphology of congenital neck masses help narrow the differential diagnosis. Given the superficial nature of neck masses and patient age, initial work-up with ultrasound is ideal. Axial imaging is helpful for delineating presurgical anatomy or when ultrasound findings are equivocal. AR