Applied Radiology

Dr. Matamoros is with the Department of Radiology; Drs. Lydiatt are with the Department of Otolaryngology-Head and Neck Surgery; and Ms. Mahoney is a medical student at the University of Nebraska Medical Center, Omaha, NE.

Neck masses in children are common and can be evaluated by various imaging modalities. Ultrasound is usually the initial imaging modality used for locating and identifying a neck mass and for determining solid versus cystic components. Computed tomography (CT) and magnetic resonance imaging (MRI) are effective imaging techniques for noninvasive evaluation of a neck mass and its relationship to adjacent soft tissues and bony structures. MRI has distinct advantages over CT, since it uses no ionizing radiation, has multiplanar capability, and has much better intrinsic soft-tissue contrast. MRI takes more time to image, however, which can be difficult in pediatric patients. The imaging modalities selected should complement the clinical evaluation of the neck mass in a patient. This article will present a brief overview of neck masses in children and give examples of those more commonly seen in pediatric patients.

The vast majority of neck masses in children are benign lesions. ^1,2 Despite this, special concern should be given for the possibility of a malignancy. In the United States each year, cancer is diagnosed in 1 in 333 persons younger than 20 years of age. It affects 7,500 children prior to age 15 and 3,500 young adults between 15 and 20 years of age. ³ Cancer is second only to accidents as the most common cause of death after the first year of life. ⁴ The etiologies of these pediatric neck masses can be organized into three general categories: congenital, inflammatory, and neoplastic. The latter is subdivided into benign and malignant neoplasms.

Congenital neck masses

A neck mass present at birth is likely to be a congenital cyst or a benign lesion. Malignant masses in neonates are very rare. Not all congenital neck masses are recognized in the neonatal period. Some congenital neck masses are not discovered until adulthood, usually following an infection which leads to enlargement. A neck mass that grows slowly is likely to be congenital or benign. More rapidly growing neck masses that usually occur within 2 months are likely to be malignant. ⁵

Thyroglossal duct cyst--Thyroglossal duct cysts result from persistence of the embryonic thyroglossal duct that connects the foramen cecum at the base of the tongue to the thyroid gland. The majority of these thyroglossal duct cysts present in childhood but can be aysmptomatic and be seen in adults. Up to one-third of these masses may present after age 20. ^6,7

The thyroglossal duct cyst is usually located in the midline of the neck at or below the level of the hyoid bone. At times, these neck masses can be seen located lateral to the midline. Lymph nodes and a dermoid cyst can mimic a thyroglossal duct cyst (figure 1). On CT scans, an uncomplicated thyroglossal duct cyst demonstrates well-defined walls, and near water attenuation value of the cystic component. If infected, the internal fluid within these cystic lesions increases in attenuation value and the walls become thicker and enhance following the administration of intravenous contrast. On MR imaging, these thyroglossal duct cysts show low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.

Branchial cleft cyst--Branchial cleft cysts arise from failure of obliteration of embryologic bronchial tissues. These anomalies arising from the bronchial system can give rise to branchial cleft cysts, sinuses, or fistulae. Branchial cleft cysts can be recognized in later childhood or in early adulthood, though at times they become apparent due to superimposed infection (figure 2). Approximately 90% of bronchial abnormalities arise from the second branchial cleft, 8% from the first branchial cleft, and the remainder from the third branchial cleft. ^8-10 The branchial cleft cyst is commonly located along the anterior border of the sternocleidomastoid muscle. About 5% of these branchial cleft cysts are bilateral. ⁸ Suppurative thyroiditis in children may be due to infected thyroglossal duct cysts and third branchial cleft cysts. ^11,12

On CT, uninfected branchial cleft cysts appear as a thin-walled, well-marginated, low-attenuation cystic masses. If the branchial cleft cyst becomes infected, the walls become thicker and are less well marginated with inflammatory changes seen in adjacent soft-tissues. The cystic component increases in attenuation value. On MRI, these lesions appear slightly hyperintense to muscle on T1-weighted images and are hyperintense on T2-weighted images.

Lymphangiomas--Lymphangiomas arise from abnormal development of primordial lymphatic channels. Histologically, these lesions are divided into three types: simple, cavernous, and cystic. Sixty-five percent of lymphatic malformations are present at birth, and 90% present by the end of the second year of life. ¹³ Some of these lesions may present later in life with acute enlargement that may be due to inflammation from an upper respiratory infection or from hemorrhage into the cystic mass. These lesions tend not to involute over time, as can be seen in hemangiomas. On CT, uncomplicated lymphangiomas are non-enhancing, low dense lesions. On T1-weighted images, lymphangiomas usually have a low signal, but can also present with high signal if there is fat or methemoglobin. On T2-weighted images, these lesions have high signal intensity (figure 3).

Hemangiomas--Hemangiomas are classified as capillary or cavernous. These lesions present within the first 6 months of life, followed by a period of rapid growth, and then undergo spontaneous slow regression. Hemangiomas are subcutaneous masses, or may present as a cutaneous lesion, both accounting for the bluish discoloration. Variable degrees of enhancement can be seen following the administration of intravenous contrast on CT and MRI scans.

Ranulas--A ranula is an abnormal cystic dilatation of an obstructed sublingual or minor salivary gland in the floor of the mouth. ¹⁴ Two types of ranulas can be seen: simple and plunging. The simple ranula is more common and is located in the sublingual space. The plunging ranula descends beyond the mylohyoid muscle and into the lower neck. On CT, the simple ranula shows thin-walled, well-marginated, low density, nonenhancing cystic mass cephalad to the mylohyoid muscle. A plunging ranula tends to have less well-defined margins and has a higher attenuation value of its contents (figure 4). ¹⁴ On MRI, ranulas tend to have a low signal on T1-weighted images and high signal intensity on T2-weighted images.

Dermoids/teratomas-- Dermoid cysts arise from endoderm and mesoderm germ cell layers. The internal contents include epidermal appen-dages such as sebaceous glands, hair, and hair follicles. Occasionally, focal calcification can be see within the lesion. These cystic masses tend to be located above the level of the hyoid. ⁹ The internal contents of the cystic mass will dictate their appearance on CT and MRI. On CT, the low attenuation values are due, in part, to the fatty tissue from the germ cell layers. MRI will show the low signal from the fatty tissue.

Teratomas contain tissue elements from all three germ layers. These lesions are usually present at birth and 20% are associated with maternal polyhydramnios. ¹⁵ Teratomas tend to be located off the midline next to the thyroid gland or project within it. Teratomas present with similar imaging characteristics as dermoids.

Inflammatory neck masses

Cervical adenitis--Benign cervical adenopathy is most common cause of neck masses in children. The lymphadenitis may be due to bacterial, viral, fungal, parasitic, or noninfectious etiologies. These nodes are likely to be located in the submandibular or deep cervical nodes in 80% of children. ¹⁶ An upper respiratory tract infection tends to be the most common cause for the cervical lymphadenopathy. The most common cause for bacterial cervical lymphadenopathy is Staphylococcus aureus and group A streptococci. ^17,18 Cellulitis and abscess formation are the two most common complications of cervical infections. CT will likely be the imaging study used to evaluate the cervical soft tissues. On CT, cellulitis presents as a nidus of soft-tissue swelling with loss of adjacent soft tissue planes and no obvious necrotic center. An abscess will show an enhancing ring surrounding a low dense focus of necrotic tissue with or without gas present within the necrotic tissue (figure 5). An abscess tends to have a low signal on T1-weighted images and high signal on T2-weighted images.

Mycobacterial cervical adenitits can be another cause of cervical adenopathy in pediatric patients. Both tuberculous and nontuberculous mycobacteria are etiologic agents. On CT, the cervical adenopathy likely will be a clustered collection of lymph nodes, showing central necrosis, rim enhancement, adjacent inflammatory changes, and occasional calcifications.

Other causes of infectious cervical adenitis include cat-scratch fever, tularemia, mononucleosis, and fungal and parasitic infections. Noninfectious inflammatory cervical adenitis can be seen in Kawasaki disease, sarcoidosis, sinus histiocytosis with massive lymphadenopathy, ¹⁹ and the FAPA syndrome (periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis). ²⁰

Acquired immunodeficiency syndrome (AIDS) is another cause for cervical adenitis. The consideration of HIV infection is warranted when there is cervical adenitis, nasopharyngeal hyperplasia, and cystic parotid lesions that can be seen on CT and MRI evaluation. ^21,22

Malignant neoplasms

Malignant neoplasms in the pediatric population are uncommon. In a study of 445 children who underwent excision of any neck mass (including lymph nodes), Torsiglieri et al ¹ found 55% congenital masses, 27% inflammatory lesions, 5% non-inflammatory benign lesions, 3% benign neoplasms, and 11% malignancies. The majority of pediatric malignancies are due leukemias and lymphomas (48%) and central nervous system tumors (20%). ²³ In the United States, lymphomas account for more than 50% of pediatric neck malignancies, ^1,24 and rhabdomyosarcomas represent the most common pediatric soft-tissue malignancy of the head and neck. ²⁵ The two more common lymphomas include Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL). Non-Hodgkin's lymphoma accounts for 60% of newly diagnosed lymphomas. ²⁶ Lymphoma commonly presents with painless cervical ad-enopathy. Upper-neck lymph nodes are more commonly involved than lower-neck lymph nodes. Hodgkin's disease also presents as a painless mass but usually of the lower neck and supra-clavicular fossa.

Hodgkin's disease--Even though HD is less common than NHL, it presents more frequently in the neck due to its unusual pattern of extranodal involvement which is a more common pattern with NHL. HD is more commonly seen after the age of 15 years and is rare before the age of 10, and it is more common in males. ²⁷ On CT, these lymph nodes may be individually enlarged or present as a cluster of matted lymph nodes. A low dense center is consistent with necrosis (figure 6). This CT appearance can mimic lymph nodes involved with infection. On MRI, the involved lymph nodes tend to be isointense to muscle on T1-weighted images and hyperintense to muscle on T2-weighted images.

Non-Hodgkin's lymphoma--The peak incidence of NHL in children is between 7 and 11 years of age. ²⁸ The male to female ratio is 3:1 with a Caucasian to African-American ratio of 2:1. ²⁹ Childhood NHL tends to be more malignant, poorly differentiated, and a more clinically aggressive tumor when compared with that of adults. NHL is more likely to be disseminated and extranodal. The CT and MRI findings are typical to those seen with HD.

Rhabdomyosarcomas--Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood and 35% to 40% arise in the head and neck. ^30,31 The peak incidence of these tumors occurs between 2 and 5 years with a secondary peak between 15 and 19 years of age. ³² RMS tend to be aggressive and infiltrating neoplasms. Orbital and skull base RMS are more common than primary cervical RMS, with less than 10% of those with primary head RMS developing cervical lymph node metastasis. ³³ CT and MRI can be used for local staging; MRI, with its inherent soft-tissue contrast is better at delineating the involved soft tissues. On CT, RMS presents as a soft-tissue mass, with variable internal necrosis or rim enhancement. On MRI, the involved soft tissues are better seen with low signal on T1-weighted images and high signal on T2-weighted images. High signal can also be seen on T1-weighted images if there has been hemorrhage or a biopsy prior to MR imaging. Contrast en-hancement of the tumor margins can be seen with gadolinium.

Neuroblastoma--Approximately 2% to 4% of neuroblastomas occur in the neck. ³⁴ These tumors arise from primitive neuroblasts and neural crest cells and are the second most common solid tumor of childhood occurring before 5 years of age. Aside from a cervical mass or adenopathy, a Horner's syndrome may be present. Since neuroblastoma is considered to have systemic involvement, CT and MRI are used to evaluate for metastatic disease, with CT better for evaluation of the chest and abdomen. On CT, neuroblastoma presents as a paraspinal low attenuation soft-tissue mass with one-half of the tumors containing calcifications. ³⁵ MRI is better at identifying intraspinal involvement. On MRI, neuroblastoma shows an intermediate signal on T1-weighted images and slightly higher signal on T2-weighted images. Neuroblastomas enhance after contrast administration.

Thyroid carcinoma

Up to 3% of pediatric malignancies are due to thyroid carcinoma. ^36-38 The majority of these tumors occur between 15 and 19 years of age with a female to male ratio of 2:1. ³⁹ On clinical presentation, 70% to 90% of these patients present with cervical lymphadenopathy ³⁹ and histologic examination reveals that nearly 90% have cervical lymph node metastases. ³⁹ Papillary carcinoma (>70%) is the most common type, followed by follicular type (15% to 20%), medullary type (3% to 10%), and anaplastic type (3%). ^39,40 Low dense masses, with variable defined margins and calcifications, can be seen on CT evaluation. Metastatic disease to lymph nodes can demonstrate central necrosis and calcifications.

Other malignancies--Other pediatric neck malignancies that may be seen include: other soft tissue sarcomas, nasopharyngeal malignancies, salivary gland neoplasms, and metastatic disease.

Conclusion

Pediatric neck masses are common and most of these are benign diseases. CT and MRI can be used effectively to complement the clinical evaluation and help guide individual patient management. CT and MRI each have particular imaging characteristics that should be taken into account in the evaluation of pediatric neck masses.

References

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