2017 Sec 1 Green Book

sus, and acute paramyxovirus parotitis. These conditions can be identified by detection of antibodies or based on serology. 51 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. 50 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. 54 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. 54 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%). 55 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. 56 Rhabdomyosar- comas, liposarcomas, and aggressive fibromatosis are also reported in the salivary gland. 55 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. 55 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

(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. 45 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. 47 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. 48 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 to 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 of 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. 53 The radiological differential diagnosis includes benign lymphoepithe- lial cyst, juvenile Sj¨ogren syndrome, systemic lupus erythemato-

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