(Radiographics. 2001;21:1211-1227.)
© RSNA, 2001
Swelling at the Angle of the Mandible: Imaging of the Pediatric Parotid Gland and Periparotid Region1
Lisa H. Lowe, MD,
Leanne S. Stokes, MD,
Joyce E. Johnson, MD,
Richard M. Heller, MD,
Stuart A. Royal, MD,
Curt Wushensky, MD and
Marta Hernanz-Schulman, MD
1 From the Department of Radiology, Children’s Mercy Hospital, University of Missouri–Kansas City, 2401 Gillham Rd, Kansas City, MO 64108 (L.H.L.); the Departments of Radiology and Radiological Sciences (L.S.S., R.M.H., C.W., M.H.S.) and Pathology (J.E.J.), Vanderbilt Children’s Hospital, Nashville, Tenn; and the Department of Radiology, Children’s Hospital of Alabama, Birmingham (S.A.R.). Presented as an education exhibit at the 2000 RSNA scientific assembly. Received February 27, 2001; revision requested March 21 and received May 11; accepted May 14. Address correspondence to L.H.L. (e-mail: llowe@cmh.edu).
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Abstract
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The pediatric parotid gland and periparotid region are subject to a variety of lesions and are most often evaluated with ultrasonography (US), contrast material–enhanced computed tomography (CT), and magnetic resonance (MR) imaging. US may be used to assess the size of the parotid gland, distinguish diffuse from focal disease, assess vascularity and adjacent vascular structures, distinguish cystic from solid lesions, and guide fine-needle aspiration. However, further evaluation with CT or MR imaging may be needed to better define the nature and extent of disease. CT is the imaging modality of choice for most pediatric parotid disease (including acute inflammation, abscess, calculi, and major salivary duct obstruction) and most solid masses and may obviate sedation. However, a mass associated with facial nerve symptoms should be evaluated with MR imaging because it is the only modality that can consistently demonstrate the facial nerve. Findings at US, CT, and MR imaging allow localization of parotid lesions and may suggest a specific cause. Clinical information, familiarity with normal parotid anatomy at various stages of its development, and knowledge of the imaging characteristics of parotid and periparotid lesions are essential for appropriate radiologic evaluation. This information can be used to guide therapy and plan a surgical approach.
Index Terms: Branchial cleft, 2641.1471 • Parotid gland, 2641.20, 2641.219, 2641.22, 2641.23, 2641.242, 2641.696, 2641.92 • Parotid gland, neoplasms, 2641.34, 2641.36, 2641.37 • Radiography, in infants and children, 2641.1211, 2641.1214, 2641.1298
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Describe the normal anatomy of the parotid gland at various stages of development.
- Formulate an imaging approach to pediatric parotid lesions with modalities such as US, helical CT, and MR imaging.
- Recognize the imaging appearance of a variety of pediatric parotid and periparotid lesions.
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Introduction
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Children may present at any age with swelling at the angle of the mandible owing to various parotid lesions. Clinical history, such as the patient’s age at presentation, and key imaging features may narrow the differential diagnosis and possibly suggest a specific diagnosis. This information in turn has implications for therapy and prognosis.
In this article, we review parotid embryology and normal parotid anatomy, relevant imaging approaches and techniques (ultrasonography [US], computed tomography [CT], magnetic resonance [MR] imaging), and key clinical and imaging features of various congenital, neoplastic, and inflammatory lesions of the parotid gland and immediate periparotid region (Table).
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Parotid Embryology
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The parotid gland is composed of secretory parenchymal tissue (ectoderm) and stromal tissue (mesoderm). The glandular components arise from an ingrowth of local proliferation of oral epithelium, which canalizes and creates ducts by the 10th week of gestation. Parotid secretions begin by the 18th week (1).
The development of the parotid gland is unique in two ways compared with that of the other major salivary glands. First, it is the only salivary gland to become encapsulated after the development of the lymphatic system, resulting in the presence of both intraparotid lymph nodes and lymphatic channels. The inclusion of both salivary and lymphatic tissues may play a role in the development of Warthin tumors, which occur only in the parotid gland and periparotid region (2). Second, during embryogenesis epithelial buds branch around divisions of the facial nerve, thus incorporating it into the parotid parenchyma (1).
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Normal Parotid Anatomy
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The parotid gland is located at the angle of the mandible, defining an anatomic area termed the parotid space, which contains the facial nerve, the retromandibular vein, the external carotid artery and its branches, and intraparotid lymph nodes (3). The parotid gland wraps around the angle of the mandible, with the majority of the gland lying superficial to the masseter muscle (Fig 1). Although the parotid parenchyma is not anatomically divided into lobes, the gland may theoretically be subdivided by the facial nerve into superficial and deep lobes for the purpose of surgical approach. Unlike the superficial lobe, the deep lobe lies deep to the angle of the mandible. The parotid gland is drained by the Stenson duct, which exits above the upper second molar tooth (1,3,5,6). The facial nerve, although often not visualized at imaging, is located lateral to the posterior belly of the digastric muscle and the retromandibular vein (Fig 2) (7).
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Figure 1. Schematic demonstrates gross parotid anatomy. A portion of the superficial parotid lobe has been removed to show its relationship with the facial nerve and retromandibular vein, which divide the parotid gland into superficial and deep lobes. M = masseter muscle. (Reprinted, with permission, from reference 4.)
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Figure 2a. (a, b) Normal upper parotid space anatomy. (a) Schematic illustrates normal anatomy. (b) CT scan in a 6-month-old girl shows the parotid gland (P) with an attenuation similar to that of adjacent muscle. E = external carotid artery, I = internal carotid artery, J = internal jugular vein, M = masseter muscle, R = retromandibular vein,  = fat-filled parapharyngeal space. (c, d) Lower parotid space anatomy. (c) Schematic illustrates normal anatomy. (d) CT scan in a 17-year-old boy shows the parotid gland (P) with low attenuation due to normal fatty replacement. E = external carotid artery, M = masseter muscle, R = retromandibular vein, S = styloid process, = fat-filled parapharyngeal space. (Reprinted, with permission, from reference 7.)
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Figure 2b. (a, b) Normal upper parotid space anatomy. (a) Schematic illustrates normal anatomy. (b) CT scan in a 6-month-old girl shows the parotid gland (P) with an attenuation similar to that of adjacent muscle. E = external carotid artery, I = internal carotid artery, J = internal jugular vein, M = masseter muscle, R = retromandibular vein, = fat-filled parapharyngeal space. (c, d) Lower parotid space anatomy. (c) Schematic illustrates normal anatomy. (d) CT scan in a 17-year-old boy shows the parotid gland (P) with low attenuation due to normal fatty replacement. E = external carotid artery, M = masseter muscle, R = retromandibular vein, S = styloid process, = fat-filled parapharyngeal space. (Reprinted, with permission, from reference 7.)
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Figure 2c. (a, b) Normal upper parotid space anatomy. (a) Schematic illustrates normal anatomy. (b) CT scan in a 6-month-old girl shows the parotid gland (P) with an attenuation similar to that of adjacent muscle. E = external carotid artery, I = internal carotid artery, J = internal jugular vein, M = masseter muscle, R = retromandibular vein, = fat-filled parapharyngeal space. (c, d) Lower parotid space anatomy. (c) Schematic illustrates normal anatomy. (d) CT scan in a 17-year-old boy shows the parotid gland (P) with low attenuation due to normal fatty replacement. E = external carotid artery, M = masseter muscle, R = retromandibular vein, S = styloid process, = fat-filled parapharyngeal space. (Reprinted, with permission, from reference 7.)
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Figure 2d. (a, b) Normal upper parotid space anatomy. (a) Schematic illustrates normal anatomy. (b) CT scan in a 6-month-old girl shows the parotid gland (P) with an attenuation similar to that of adjacent muscle. E = external carotid artery, I = internal carotid artery, J = internal jugular vein, M = masseter muscle, R = retromandibular vein, = fat-filled parapharyngeal space. (c, d) Lower parotid space anatomy. (c) Schematic illustrates normal anatomy. (d) CT scan in a 17-year-old boy shows the parotid gland (P) with low attenuation due to normal fatty replacement. E = external carotid artery, M = masseter muscle, R = retromandibular vein, S = styloid process, = fat-filled parapharyngeal space. (Reprinted, with permission, from reference 7.)
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At US, the normal pediatric parotid gland is homogeneous and hyperechogenic relative to adjacent muscle (Fig 3) (5). In young children, the parotid parenchyma is similar to muscle and fat in attenuation and signal intensity at CT and MR imaging, respectively. With age, the parotid gland undergoes progressive fatty infiltration, becoming more hypoattenuating at CT and fat replaced at MR imaging. The MR imaging appearance changes to reflect increased fat content (Fig 4). Knowledge of this normal pattern can prevent misdiagnosis of an "infiltrative parotid tumor" in young children. An accessory parotid gland represents a potential pitfall in that it may be mistaken for a mass (1,6). An accessory parotid gland is present in as many as 20% of patients and drains directly into the parotid duct. It lies superficial to the masseter muscle and anterior to the main parotid gland (Fig 5).
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Figure 3. Normal parotid gland in a 3-year-old girl. Longitudinal parotid US image obtained in the coronal plane (cranial, right; caudal, left) demonstrates a homogeneous, hyperechogenic parotid gland (P) at the angle of the mandible (M). Arrow indicates the retromandibular vein, arrowhead indicates the external carotid artery. = masseter muscle.
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Figure 4a. Normal parotid gland in an 18-year-old man. Axial short-TR (a) and long-TR (b) MR images demonstrate the parotid gland (P), parotid duct (black arrows in a), and parapharyngeal space (white arrow). D = posterior belly of digastric muscle, I = internal carotid artery, J = jugular vein, M = masseter muscle, R = retromandibular vein, S = sternocleidomastoid muscle.
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Figure 4b. Normal parotid gland in an 18-year-old man. Axial short-TR (a) and long-TR (b) MR images demonstrate the parotid gland (P), parotid duct (black arrows in a), and parapharyngeal space (white arrow). D = posterior belly of digastric muscle, I = internal carotid artery, J = jugular vein, M = masseter muscle, R = retromandibular vein, S = sternocleidomastoid muscle.
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Figure 5. Accessory parotid gland in an 18-year-old woman who had undergone left parotidectomy at age 5 years for an unspecified neoplasm. CT scan demonstrates an accessory parotid gland (white arrow) with characteristic architecture and partial fatty replacement. Black arrow indicates the styloid process. M = masseter muscle.
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Imaging Considerations
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At present, the three imaging methods most often used to evaluate the parotid gland are US, contrast material–enhanced CT, and MR imaging. Sialography retains a role in the evaluation of autoimmune and chronic inflammatory disease but is beyond the scope of this article (7,8). US may be used to assess the size of the parotid gland, distinguish diffuse from focal disease, assess vascularity and adjacent vascular structures, distinguish cystic from solid lesions, and guide fine-needle aspiration (9). However, further evaluation with CT or MR imaging may be needed to better define the nature and extent of disease. Because of the rapidity of the study, CT is the imaging modality of choice for most pediatric parotid disease (including acute inflammation, abscess, calculi, and major salivary duct obstruction) and most solid masses and may obviate sedation. However, a mass associated with facial nerve symptoms should be evaluated with MR imaging because it is the only modality that can consistently demonstrate the facial nerve (7,10,11).
US is performed with a linear transducer, usually at a frequency between 6 and 10 MHz depending on patient age and size. The transducer is initially placed at the angle of the mandible, just below the ear. The parotid gland is readily identified as a hyperechogenic structure. The superficial lobe can be followed as it extends anteriorly and cephalad, anterior to the ear and posterior to the masseter muscle. In contrast, visualization of the deep lobe requires that the transducer be directed superiorly to insonate the area deep to the mandibular angle. At color Doppler US, the parotid parenchyma demonstrates a small amount of flow but is not hypervascular.
CT of the pediatric parotid gland at our institution may include axial imaging both before and after intravenous administration of contrast material. Postcontrast images are mandatory, and precontrast images should be included if calcification or bone destruction is suspected. Collimation at helical CT is usually 3 mm (pitch of 1) but can be adjusted to 5 mm for precontrast imaging depending on patient age and size. The gantry angle should be parallel to the anthropologic baseline, with adjustments to avoid artifact created by orthodontics and dental fillings. Contrast material is administered intravenously at a rate of 2 mL/kg. Coronal CT may be useful in specific cases but is not routinely performed at our institution.
Although MR imaging protocols vary among institutions, our protocol includes axial and coronal short-repetition-time (short-TR) (2 signals acquired), axial fast spin-echo long-TR, and axial and coronal contrast-enhanced fat-suppressed short-TR sequences. The section thickness is 3–5 mm, the field of view is adjusted for patient size, the acquisition matrix is typically 256 x 192, and flow compensation is always used.
Fine-needle aspiration of parotid and periparotid lesions has proved useful in adults. However, its usefulness in children has not been as clearly established. If clinical and radiologic findings do not suggest a specific diagnosis that does not require intervention (ie, hemangioma, parotitis, adenitis, abscess), fine-needle aspiration may be considered. In adults, fine-needle aspiration has been most useful in benign primary parotid lesions such as pleomorphic adenoma, which are less common in children. The need for fine-needle aspiration in children is considered in light of the need for sedation or potential surgical procedures that may inevitably be required.
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Branchial Cleft Cyst
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At the 5th week of gestation, four paired branchial clefts and pouches are present along the pharyngeal wall (12). The first cleft and pouch contribute to the formation of the external auditory canal, middle ear, and pharyngotympanic tube. The second through fourth pouches give rise to the palatine tonsils, parathyroid glands, and thymus, whereas the clefts subsequently involute (12–14). Failure of involution leads to branchial cleft cysts, fistulas, or sinus tracts, which may occur superficially from the skin surface along the anterior border of the sternocleidomastoid muscle to the deeper cervical recesses along the lateral wall of the pharynx (14,15). Sinus tracts and fistulas found in association with a branchial cleft cyst are usually located lateral and external to the cyst. Branchial cleft cysts usually manifest with painless fluctuant swelling (13). Infection may initiate this swelling, causing a more acute, painful presentation (14,15).
Branchial cleft cysts are most often classified based on the cleft or pouch of origin (ie, first through fourth). First branchial cleft cysts are rare, are located in the parotid gland or immediate periparotid region, and may have a direct connection with the external auditory canal (6,13). Second branchial cleft cysts are common and have been divided into four types according to the Bailey classification system, which is based on anatomic relationships. Type I second branchial cleft cysts are found anterior to the sternocleidomastoid muscle under the platysma and cervical fascia. Type II cysts are the most common; they are located adjacent to and may adhere to the great vessels at the mandibular angle. Type III cysts are found between the internal and external carotid arteries adjacent to the pharynx. Type IV second branchial cleft cysts are found against the pharyngeal wall. Third and fourth branchial cleft cysts are extremely rare and are found adjacent to the laryngeal ventricle, posterior to the common carotid artery and jugular vein at the margin of the sternocleidomastoid muscle. Fourth branchial cleft cysts are more common on the right side and are found along the course of the recurrent laryngeal nerve, especially anterior and inferior to the subclavian artery.
At US, features typical of a cyst are seen. However, when the cyst is filled with particulate material (most often due to internal hemorrhage or infection), it may simulate a solid lesion. Doppler US will demonstrate complete lack of internal flow, establishing its cystic nature (16). A well-defined, fluid-attenuation lesion with slight enhancement of the capsule is seen at contrast-enhanced CT (Fig 6) (13). The sternocleidomastoid muscle may extend around the margins of the cyst in a beaklike configuration. Infection within the cyst may cause thickening and enhancement of the wall (Fig 7). The cyst is hypointense with short-TR and hyperintense with long-TR MR imaging sequences, although some increased signal intensity may be present with short-TR sequences owing to internal particulate debris due to prior bleeding or infection (1,17). The treatment of choice is complete surgical excision of the cyst and of any associated fistula or sinus tract.
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Figure 6a. Second branchial cleft cyst in a 15-year-old boy. (a) Longitudinal US image shows a well-defined, hypoechoic cyst (calipers). (b) Contrast-enhanced CT scan demonstrates a fluid-attenuation mass ().
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Figure 6b. Second branchial cleft cyst in a 15-year-old boy. (a) Longitudinal US image shows a well-defined, hypoechoic cyst (calipers). (b) Contrast-enhanced CT scan demonstrates a fluid-attenuation mass ().
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Figure 7. Second branchial cleft cyst complicated by infection in an 18-year-old woman. Contrast-enhanced CT scan reveals a well-defined, fluid-attenuation mass with a thick rim of enhancement (arrows).
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Neoplasms
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Tumors of the salivary glands are uncommon in children, accounting for only 1% of all pediatric neoplasms (5). From 90% to 95% of salivary tumors occur in the parotid gland, and 5% occur in the submandibular and sublingual glands (5,11,18). Up to 65% of salivary gland neoplasms in children are benign, whereas a greater proportion of malignant lesions occurs in adults (10,19). Unlike in adults, the larger the gland of origin in children, the more likely that a tumor will be malignant.
Hemangioma
Hemangiomas are the most common benign salivary gland mass in children and have a significant female predilection (5). They are classified at pathologic analysis as capillary or cavernous. Congenital capillary hemangiomas represent 90% of parotid gland tumors during the 1st year of life, whereas cavernous hemangiomas rarely involve the parotid gland (1). Capillary hemangiomas manifest as a soft mass noted shortly after birth (6). They grow rapidly during the 1st year of life, peak at age 1–2 years, and then undergo slow spontaneous regression that is usually complete by adolescence (20). At histologic analysis, capillary hemangiomas are composed of an unencapsulated mass of closely packed, thin-walled capillaries with plump endothelial cells. Cavernous hemangiomas may manifest in older children, do not undergo spontaneous resolution, and are composed of large, thin-walled vessels with flattened endothelial cells (1,21).
Hemangiomas are usually hypoechoic relative to parotid tissue at US and display a variable degree of abnormal flow at Doppler US. Contrast-enhanced CT of capillary hemangiomas demonstrates a well-defined mass with uniform, intense enhancement (Fig 8). Phleboliths are occasionally seen in cavernous hemangiomas at unenhanced CT. After contrast material administration, there is a variable pattern of enhancement. Most hemangiomas demonstrate low to intermediate signal intensity on short-TR MR images and bright signal intensity on long-TR images. Flow voids due to prominent vasculature are often present in and around the mass and will demonstrate intense enhancement after contrast material administration (1,5,6). Because most capillary hemangiomas spontaneously regress, surgical treatment is delayed as long as possible unless there are extenuating circumstances related to the size of the mass and encroachment on adjacent structures (6). Treatment options for cavernous hemangiomas are variable and include surgery, sclerotherapy, laser ablation, or a combination of these treatments, which are often repeated depending on the specific lesion.
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Figure 8a. Capillary hemangioma in a 2-month-old boy with increasing left cheek swelling since birth. (a) Coronal US image (cranial, left; caudal, right) demonstrates a solid, hypoechoic parotid mass (calipers). (b) Axial CT scan reveals a hypervascular mass with intense homogeneous enhancement (solid arrows) replacing the parotid gland. Note the deep lobe involvement with widening of the stylomandibular foramen (bracket) and extension into the parapharyngeal space (open arrow).
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Figure 8b. Capillary hemangioma in a 2-month-old boy with increasing left cheek swelling since birth. (a) Coronal US image (cranial, left; caudal, right) demonstrates a solid, hypoechoic parotid mass (calipers). (b) Axial CT scan reveals a hypervascular mass with intense homogeneous enhancement (solid arrows) replacing the parotid gland. Note the deep lobe involvement with widening of the stylomandibular foramen (bracket) and extension into the parapharyngeal space (open arrow).
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Lymphangioma
Lymphangiomas are congenital malformations of the lymphatic system that may involve the parotid gland. Approximately 65% of lymphangiomas are present at birth, and 90% are detected by age 2 years (1,6,13). They typically manifest as a soft, asymptomatic neck mass, and facial asymmetry is common (20). Infection or hemorrhage may complicate lymphangiomas, which unlike hemangiomas rarely undergo spontaneous regression (5,20). At pathologic analysis, lymphangiomas are classified on the basis of the size of the cystic spaces as lymphangioma simplex, cavernous lymphangioma, or venolymphatic malformations (Fig 9) (20).
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Figure 9a. Lymphangioma. (a) Photograph of a gross specimen shows the multilocular, thin-walled cystic appearance that is typical of lymphangioma. (b) Photomicrograph (original magnification, x31.5; hematoxylin-eosin [H-E] stain) demonstrates irregular thin-walled, slitlike spaces of varying sizes with a flat endothelial lining, admixed with fat. A small focus of uninvolved salivary tissue is also seen (arrow).
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Figure 9b. Lymphangioma. (a) Photograph of a gross specimen shows the multilocular, thin-walled cystic appearance that is typical of lymphangioma. (b) Photomicrograph (original magnification, x31.5; hematoxylin-eosin [H-E] stain) demonstrates irregular thin-walled, slitlike spaces of varying sizes with a flat endothelial lining, admixed with fat. A small focus of uninvolved salivary tissue is also seen (arrow).
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At US, lymphangiomas typically appear cystic with thin septations, although solid elements may be present (5). At CT, lymphangiomas are heterogeneous with septations and cystic areas. The mass is often multispatial and insinuates itself between adjacent structures. It often contains fluid-fluid levels, and solid portions of the lesion may enhance. At MR imaging, lymphangiomas are heterogeneous with multiple cystic areas demonstrating low signal intensity with short-TR sequences and high signal intensity with long-TR sequences. Hemorrhage into the lesion frequently occurs, causing multiple fluid-fluid interfaces with variable signal intensity depending on the age of the blood products (Fig 10). This imaging feature, although not always present, strongly suggests a diagnosis of lymphangioma rather than hemangioma. Contrast-enhanced imaging may show enhancement of the solid portions of the lesion but is not required when a typical multispatial, multicystic mass with blood-fluid interfaces is seen (20). Treatment options include surgical debulking or resection, sclerotherapy, and interferon injection. However, complete resolution may not be possible due to the extent of involvement and the multispatial character of the lesion. In addition, recurrence due to residual lymphatic malformation is not uncommon.
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Figure 10a. Lymphangioma in a 13-month-old boy. (a) Transverse US image shows a hypoechoic multiloculated mass (). (b) Fat-suppressed long-TR MR image helps confirm a multiloculated mass with fluid levels and variable signal intensity (arrows). The mass is seen infiltrating the parotid, parapharyngeal, and masticator (M) spaces.
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Figure 10b. Lymphangioma in a 13-month-old boy. (a) Transverse US image shows a hypoechoic multiloculated mass (). (b) Fat-suppressed long-TR MR image helps confirm a multiloculated mass with fluid levels and variable signal intensity (arrows). The mass is seen infiltrating the parotid, parapharyngeal, and masticator (M) spaces.
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Pleomorphic Adenoma (Mixed Tumor)
Pleomorphic adenoma is the third most common tumor of the pediatric parotid gland following hemangioma and lymphangioma. This tumor typically manifests as a hard, painless, slow-growing mass. Pleomorphic adenomas occur in patients 1–20 years of age (median, 15 years) (11,18). As the alternate term mixed tumor implies, architectural heterogeneity is the dominant histologic feature of pleomorphic adenomas (Fig 11) (21).
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Figure 11a. Pleomorphic adenoma. (a) Photograph of a gross specimen shows a pleomorphic adenoma with a smooth border and a homogeneous cut surface without scarring or necrosis. Note the attached normal salivary tissue (SG). (b) Photomicrograph (original magnification, x62.5; H-E stain) shows an admixture of epithelial (E) and chondromyxoid (C) elements. = capsule.
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Figure 11b. Pleomorphic adenoma. (a) Photograph of a gross specimen shows a pleomorphic adenoma with a smooth border and a homogeneous cut surface without scarring or necrosis. Note the attached normal salivary tissue (SG). (b) Photomicrograph (original magnification, x62.5; H-E stain) shows an admixture of epithelial (E) and chondromyxoid (C) elements. = capsule.
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At US, pleomorphic adenomas appear hypoechoic to isoechoic relative to the rest of the parotid gland. They may contain small calcifications seen as hyperechogenic shadowing foci (5). CT and MR imaging findings in pleomorphic adenoma vary depending on tumor size. Smaller tumors are more homogeneous and well-defined, whereas larger tumors are often less well-defined and more heterogeneous with areas of necrosis or hemorrhage. Pleomorphic adenomas mildly enhance after intravenous administration of contrast material (1,6). Smaller tumors typically demonstrate low signal intensity on short-TR MR images and high signal intensity on long-TR images, whereas larger tumors are more heterogeneous and demonstrate low to intermediate signal intensity on short-TR MR images and intermediate to high signal intensity on long-TR images (Fig 12). Pleomorphic adenomas are treated surgically with facial nerve–sparing partial parotidectomy. A high rate of recurrence follows local enucleation of the mass, which is no longer considered an option for treatment (1,6).
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Figure 12a. Pleomorphic adenoma in a 14-year-old boy. (a) Coronal short-TR MR image reveals a left parotid mass (arrow) that is hypointense relative to parotid tissue (P). (b) On a contrast-enhanced MR image, the mass demonstrates increased enhancement. P = parotid tissue.
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Figure 12b. Pleomorphic adenoma in a 14-year-old boy. (a) Coronal short-TR MR image reveals a left parotid mass (arrow) that is hypointense relative to parotid tissue (P). (b) On a contrast-enhanced MR image, the mass demonstrates increased enhancement. P = parotid tissue.
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Warthin Tumor
Warthin tumor, also known as papillary cystadenoma lymphomatosum or adenolymphoma, is the second most common benign salivary gland neoplasm in children, occurring only in the parotid gland. It manifests as a painless, slow-growing mass and is bilateral in up to 10% of cases. It is the most common lesion to manifest as unilateral, multifocal masses and is the most common salivary neoplasm to manifest as multiple masses in one or both parotid glands (2). Warthin tumors are thought to be a direct result of the unique embryologic development of the parotid gland, which allows the incorporation of lymphatic elements and heterotopic salivary gland ductal epithelium within intraparotid and periparotid nodes. The histologic features of these tumors are very characteristic, consisting of a double layer of oncocytes (epithelial cells) resting on a dense lymphoid stroma (Fig 13) (21).
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Figure 13. Warthin tumor. Photograph of a gross specimen shows an unusually large Warthin tumor (W) occupying more than half of the superficial lobe of the parotid gland. The smooth, fleshy portions represent the lymphoid stroma. Many of the nodules are cystic. Normal salivary tissue is also noted (S).
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At CT and MR imaging, Warthin tumor appears as a well-circumscribed, homogeneous cystic or solid lesion, often located in the tail of the parotid gland. Multiple or bilateral parotid or periparotid masses strongly suggest the diagnosis (Fig 14) (1,6). Although radionuclide imaging is not routinely performed for evaluation of salivary gland tumors, it may aid in the diagnosis of Warthin tumor. Warthin tumor may demonstrate increased uptake at technetium-99m pertechnetate imaging, 2-[fluorine-18]fluoro-2-deoxy-D-glucose positron emission tomography, and thallium-201 chloride single photon emission CT (22,23). The differential diagnosis includes processes that cause bilateral intraparotid nodal enlargement, such as lymphoma and inflammatory diseases. Treatment includes surgical resection, although recurrence may occur due to frequent multifocality.
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Figure 14. Warthin tumors in an 18-year-old man. Coronal contrast-enhanced fat-suppressed short-TR MR image demonstrates multiple bilateral parotid masses with enhancement (arrows).
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Angiolipoma
Angiolipoma is a benign nodular lesion that is especially rare in the parotid gland before puberty (23,24). Angiolipomas may be circumscribed or infiltrating, with the circumscribed form being more frequently encountered. This lesion is similar to ordinary lipomas except for associated angiomatous proliferation. CT can help define the lipomatous and hemangiomatous components of the lesion and demonstrates marked enhancement around the fatty components (Fig 15). It is difficult to distinguish between an angiolipoma of the parotid gland and a hemangioma with fatty degeneration. Although patient age may be helpful in this regard, the distinction may not be prognostically significant. Angiolipomas are best treated with complete surgical excision with facial nerve preservation. Recurrence rates are virtually 0% (24).
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Figure 15a. Angiolipoma in a 6-month-old girl with a gradually enlarging right cheek mass since 1 week of age. (a) Axial unenhanced CT scan demonstrates a well-circumscribed right parotid mass with low attenuation (<50 HU) (arrow). (b) On a contrast-enhanced CT scan, the parotid mass demonstrates marked enhancement with fatty elements designated as the region of interest (marker). (Reprinted, with permission, from reference 24.)
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Figure 15b. Angiolipoma in a 6-month-old girl with a gradually enlarging right cheek mass since 1 week of age. (a) Axial unenhanced CT scan demonstrates a well-circumscribed right parotid mass with low attenuation (<50 HU) (arrow). (b) On a contrast-enhanced CT scan, the parotid mass demonstrates marked enhancement with fatty elements designated as the region of interest (marker). (Reprinted, with permission, from reference 24.)
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Mucoepidermoid Carcinoma
Mucoepidermoid carcinoma is the most common malignant salivary gland neoplasm in children (5). Up to 35% of all salivary gland neoplasms in children are malignant, and 60% of these are mucoepidermoid carcinomas (6,11,25). The histologic pattern in mucoepidermoid carcinomas consists of a combination of squamous and mucous cells arranged in cords, sheets, or cystic configurations. They are classified as low-, intermediate-, or high-grade (21).
Low-grade mucoepidermoid carcinomas demonstrate smooth, "benign-appearing" margins at US, CT, and MR imaging. At CT, they may contain cystic low-attenuation areas and, rarely, focal calcifications. Low-grade mucoepidermoid carcinomas are hypointense to isointense with short-TR MR sequences and hyperintense with long-TR sequences. High-grade mucoepidermoid carcinomas tend to be more solid with fewer cystic areas and are more homogeneous at both CT and MR imaging. Mucoepidermoid carcinoma is treated surgically, with wide local excision for low-grade neoplasms and wide block excision plus radical neck dissection for high-grade neoplasms (6,10,11,18,26).
Lymphoma and Leukemia
Although rare, primary lymphoma of the salivary glands most often involves the parotid gland and is classified as a MALToma, indicating its origin from mucosal lymphoid tissue. Secondary lymphoma of the salivary glands is also rare, but like primary disease most commonly involves the parotid gland (1). Imaging characteristics of parotid gland lymphoma reflect the presence of focal masses or infiltrative disease. US will demonstrate intraparotid masses or diffuse infiltration characterized by an enlarged gland with altered echogenicity and increased flow. CT may also demonstrate focal masses confined to an intraparotid lymph node or diffuse parotid infiltration. CT usually demonstrates slight homogeneous enhancement following contrast material administration. Homogeneous intermediate signal intensity is seen with all MR imaging sequences (1,20).
Leukemic infiltration of the parotid gland rarely occurs (26,27). At US, the gland is diffusely enlarged with altered, variable echogenicity and increased flow (Fig 16). Variable attenuation and signal intensity are seen at CT and MR imaging, respectively. Leukemic infiltration is indistinguishable from other forms of parotid disease that may cause gland enlargement, including infiltrative lymphoma. This diagnosis is considered in the appropriate clinical setting (26,27).
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Figure 16a. Leukemia in a 2-year-old boy with bilateral cheek swelling. (a) Right longitudinal US image reveals diffuse, heterogeneous echogenicity and parotid gland enlargement. (b) On a color Doppler US image, the parotid gland is hypervascular. The left side had a similar appearance.
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Figure 16b. Leukemia in a 2-year-old boy with bilateral cheek swelling. (a) Right longitudinal US image reveals diffuse, heterogeneous echogenicity and parotid gland enlargement. (b) On a color Doppler US image, the parotid gland is hypervascular. The left side had a similar appearance.
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Neurofibroma
Neurofibromas are benign nerve sheath neoplasms that may arise from the facial nerve trunk or its branches and may therefore lie within the parotid gland. They may be solitary or multiple. Multiple or plexiform neurofibromas are seen in patients with von Recklinghausen disease (neurofibromatosis type I) (20,28). At gross pathologic analysis, neurofibromas are lobulated, fleshy masses (Fig 17). At histologic analysis, loose connective tissue fibers, particularly collagen, are randomly distributed among tapering nerve fibers with long, thin processes and darkly staining, elongated nuclei.
At CT, neurofibromas are most often ovoid, well-demarcated, homogeneous, and isoattenuating relative to muscle, but they may contain multiple small cystic areas. Neurofibromas usually demonstrate moderate enhancement following contrast material administration. At MR imaging, they usually demonstrate low to intermediate signal intensity with short-TR sequences and high signal intensity with long-TR sequences; however, they may contain heterogeneous areas of increased and decreased signal intensity, which makes them difficult to distinguish from pleomorphic adenomas outside the clinical context (Fig 18) (1,20). Plexiform neurofibromas have ill-defined margins with infiltration of surrounding tissues, are relatively isointense with short-TR sequences and hyperintense with long-TR sequences and demonstrate marked contrast enhancement (28).
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Figure 18a. Neurofibroma in a 16-year-old boy. (a) Axial short-TR MR image shows a hypointense mass (arrows) adjacent to the deep lobe of the parotid gland (P). (b) On an axial contrast-enhanced short-TR MR image, the mass shows heterogeneous enhancement (arrows). P = parotid gland.
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Figure 18b. Neurofibroma in a 16-year-old boy. (a) Axial short-TR MR image shows a hypointense mass (arrows) adjacent to the deep lobe of the parotid gland (P). (b) On an axial contrast-enhanced short-TR MR image, the mass shows heterogeneous enhancement (arrows). P = parotid gland.
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Rhabdomyosarcoma
Rhabdomyosarcoma is the most common pediatric soft-tissue sarcoma. Approximately 40% of all rhabdomyosarcomas arise in the head and neck, and the parotid gland may be involved most frequently by direct extension (20). Rhabdomyosarcoma is typically composed of undifferentiated "blue cells," with scant cytoplasm and primitive-appearing nuclei (Fig 19).
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Figure 19a. Rhabdomyosarcoma. (a) Photomicrograph (original magnification, x62.5; H-E stain) shows a typical rhabdomyosarcoma with diffuse sheetlike growth. (b) High-power photomicrograph (original magnification, x250; H-E stain) shows primitive and pleomorphic nuclei with scant, variable cytoplasm.
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Figure 19b. Rhabdomyosarcoma. (a) Photomicrograph (original magnification, x62.5; H-E stain) shows a typical rhabdomyosarcoma with diffuse sheetlike growth. (b) High-power photomicrograph (original magnification, x250; H-E stain) shows primitive and pleomorphic nuclei with scant, variable cytoplasm.
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At CT, rhabdomyosarcomas demonstrate heterogeneous attenuation and are isoattenuating relative to muscle with variable enhancement and indistinct margins following contrast material administration. MR imaging typically demonstrates a poorly defined, heterogeneous mass that is isointense relative to muscle with short-TR sequences and hyperintense with long-TR sequences and enhances diffusely following intravenous administration of contrast material (Fig 20). Contiguous soft tissues and osseous structures are often involved by means of direct invasion. Perineural spread of malignancy is common (20,28).
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Figure 20a. Rhabdomyosarcoma in an 18-year-old man who complained of a lump in the throat. (a) Axial contrast-enhanced CT scan reveals a mass with heterogeneous enhancement (arrows) involving the left masticator and parotid spaces. There is mass effect on the mandible (M), and the stylomandibular foramen is widened (bracket). (b) Axial contrast-enhanced short-TR MR image shows the mass with heterogeneous enhancement (arrows). M = mandible.
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Figure 20b. Rhabdomyosarcoma in an 18-year-old man who complained of a lump in the throat. (a) Axial contrast-enhanced CT scan reveals a mass with heterogeneous enhancement (arrows) involving the left masticator and parotid spaces. There is mass effect on the mandible (M), and the stylomandibular foramen is widened (bracket). (b) Axial contrast-enhanced short-TR MR image shows the mass with heterogeneous enhancement (arrows). M = mandible.
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Metastatic Adenopathy
Because the parotid gland undergoes encapsulation late in development, it contains lymphatic tissues including lymph nodes. These lymphatic structures may be the site of metastatic disease. Although uncommon in the pediatric population, squamous cell carcinoma, melanoma of the periauricular region, and thyroid carcinoma may metastasize to parotid gland nodes (6,29).
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Inflammation and Infection
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Parotitis and Parotid Abscess
Parotitis is the most common parotid disease in children. Mumps is by far the most common viral cause of parotitis in children (1,20). Acute bacterial (suppurative) sialoadenitis is uncommon in children but almost always involves the parotid gland (30). The condition manifests with tender swelling at the angle of the mandible. Staphylococcus aureus is the most common pathogen implicated in bacterial sialoadenitis. Premature neonates and immunosuppressed children are most often affected (19). At US, suppurative sialoadenitis manifests as an enlarged, heterogeneous parotid gland with hypoechoic foci representing intraparotid nodes or small abscesses (5). CT shows gland enlargement with diffuse enhancement after intravenous administration of contrast material (Fig 21) (1). The presence of a low-attenuation collection with peripheral enhancement suggests an abscess (Fig 22) (20). MR imaging demonstrates an enlarged parotid gland that is slightly hypointense with short-TR sequences and hyperintense with long-TR sequences (20). Bacterial parotitis and parotid abscess are treated with antibiotics and surgical drainage if necessary.
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Abstract
LEARNING OBJECTIVES FOR TEST...
