2017 Sec 1 Green Book

(70–90%), followed by follicular thyroid carcinoma (10–20%)

and medullary thyroid carcinoma (1–10%). The medullary car-

cinoma subtype is associated with multiple endocrine neoplasia

syndromes types 2a and 2b.

Thyroid carcinoma in children

tends to present at more advanced disease stages compared to

adults, with lymphatic, pulmonary, and/or osseous metastasis.

However, the prognosis is more favorable.

Suspicious imag-

ing finding on US include a pronounced hypoechoic thyroid

mass, a predominantly solid nature, disrupted eggshell calcifi-

cations, an irregular border, and “taller than wide” in shape.

Intralesional punctate echogenic foci of calcification and intra-

nodular vascularity may be detected.

45,47

In case of a suspicious

thyroid nodule, ultrasound-guided biopsy is an important diag-

nostic tool.

45–49

Sialadenitis

Sialadenitis or inflammation of the salivary gland is a poten-

tial consequence of either viral or bacterial infections or results

from inflammatory etiology. US is the first-line imaging modal-

ity of choice in the evaluation of sialadenitis in the pediatric

population. MRI is hardly ever indicated and only used as

problem-solving tool.

Acute parotitis is in the majority of cases caused by a viral in-

fection (eg, mumps virus, paromyxovirus). Acute viral parotitis

may be bilateral. The imaging characteristics are nondistinc-

tive with diffuse enlargement of the involved gland. On US, the

enlarged gland has a heterogeneous texture and is relatively hy-

poechoic. There is no ductal dilation. Bacterial infection lead-

ing to acute parotitis is more common in children younger than

1 year of age (eg, infections of the oral cavity or dental sepsis due

Staphylococcus aureus

). US imaging demonstrates unilateral in-

volvement of the parotid gland with anechoic or hypoechoic

foci due to suppuration. Enlarged intraparotid lymph nodes

may be encountered.

1,50

Chronic recurrent parotitis of childhood or juvenile recur-

rent parotitis is a noninflammatory process of the parotid gland

of unknown etiology associated with nonobstructive sialectasis.

It is the second most common cause of pediatric salivary gland

swelling after mumps. This entity results in recurrent episodes

of painful unilateral or bilateral swelling of the parotid gland

potentially with subsequent fever and general malaise. There

is a variable symptom-free interval between the episodes. The

peak age of onset of the first episode is reported to be 3–6 years

(ranging from infant to puberty). Chronic recurrent

parotitis

childhood is a self-limiting disease over a time period of 5–

10 years and in the majority of cases, there is resolution of

symptoms after puberty. US imaging is used to differentiate

recurrent parotitis of childhood from other causes of parotid

swelling (eg, sialolithiasis).

51,52

US imaging demonstrates diffuse

heterogeneous enlargement of the parotid gland with multiple

hypoechogenic foci representing sialectasis or lymphocytic in-

filtration. The texture of the involved gland remains abnormal

during the symptom-free periods. The potential value of MRI

may be to identify acute versus chronic inflammation patterns.

In case of acute inflammation, the gland appears T2 hyperin-

tense and T1 hypointense with concomitant contrast enhance-

ment, whereas chronic inflammation shows a T2 and T1 hy-

pointense parotid gland without contrast enhancement.

The

radiological differential diagnosis includes benign

lymphoepithe-

lial

cyst, juvenile

Sj¨ogren

syndrome, systemic lupus erythemato-

sus, and acute paramyxovirus parotitis. These conditions can

be identified by detection of antibodies or based on serology.

Human Immunodeficiency virus (HIV) can cause diffuse

swelling of the parotid gland in the pediatric population. The

parotid enlargement is typically bilateral and not painful. On

US, different imaging patterns are identified. Demonstration of

multiple scattered hypoechogenic foci in the gland parenchyma

is related to lymphoid infiltration of the gland. On the other

hand, large cystic lesions replacing the gland parenchyma can

be identified on US, representing benign

lymphoepithelial

cysts.

Disease involvement of the lungs is often seen in the setting of

this entity.

Salivary Gland Mass

Sialolithiasis is a frequent cause of salivary gland masses in the

adolescent population. The mass is caused by ductal obstruction

due to calculi. The calculi can be identified on US as well as

glandular sialectasis and swelling of the salivary gland.

Salivary gland neoplasms are rare in the pediatric age group

and comprise 1% of all pediatric neoplasms.

The majority

of solid salivary gland tumors in the pediatric age group are

benign lesions. The only benign lesion of salivary gland tis-

sue origin is the pleomorphic adenoma, comprising 11.6% of

all solid tumors. Imaging features include a well-defined soli-

tary mass with a capsule. On US, the echogenicity is variable.

On CT and MR imaging, the degree of enhancement is not

a consistent feature. Large pleomorphic adenomas may show

cystic changes, necrosis, and hemorrhage.

Reparative granu-

lomas are the second most common solid tumors of the salivary

gland (9.3%) followed by reactive lymph nodes and granular cell

tumors (both 7%).

Furthermore, nontuberculous mycobacte-

rial adenitis can involve the intraparotid lymph nodes and the

lymph nodes adjacent to the submandibular gland.

Malignant tumors of the salivary gland are extremely rare

in children. The most frequent malignant lesions are low-grade

mucoepidermoid carcinomas. Imaging features of malignancy

are ill-defined borders and focal areas of necrosis. OnMR imag-

ing, malignant salivary gland tumors typically show iso- to hy-

perintense T2 signal and restricted diffusion.

Rhabdomyosar-

comas, liposarcomas, and aggressive fibromatosis are also

reported in the salivary gland.

An important note is that many presumed salivary gland

masses in the pediatric age group are, in fact, branchial cyst

anomalies or vascular (lymphatic) malformations. The major-

ity of vascular lesions in the salivary gland are hemangiomas

followed by lymphangiomas.

Lipoma

Lipomas are rare in the pediatric age group. In the neck, the

posterior cervical triangle is the most frequent location. These

benign tumors of fat have characteristic imaging features of a

homogenous mass with signal intensity similar to subcutaneous

fat on all MR imaging sequences and do not show enhancement.

Fat-suppressed MR sequences confirm diagnosis (Fig 18). Lipo-

mas displace or compress adjacent anatomical structures rather

than demonstrating infiltrative extension.

1,57

Neuroblastic Tumors

Neuroblastic tumors are frequently encountered in the adrenal

region; however, 1–5% of primary neuroblastic tumors will oc-

cur in the cervical region. Metastatic neuroblastoma lesions

184