(Radiographics. 1999;19:121-146.)
© RSNA, 1999
From the Archives of the AFIP
Congenital Cystic Masses of the Neck: Radiologic-Pathologic Correlation
Kelly K. Koeller, CDR, MC, USN1,2,
Leonor Alamo, MD2,1,
Carol F. Adair, LTC, MC, USA2,3 and
James G. Smirniotopoulos, MD2
1 Departments of Radiologic Pathology (K.K.K., L.A.)
2 Otolaryngic and Endocrine Pathology (C.F.A.), Armed Forces Institute of Pathology, Alaska and Fern Sts, Bldg 54, Rm M-121, Washington, DC 20306-6000
3 Departments of Radiology and Nuclear Medicine (K.K.K., J.G.S.)
4 Pathology (C.F.A.), Uniformed Services University of the Health Sciences, Bethesda, Md.
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Abstract
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Cervical congenital cystic masses constitute an uncommon group of lesions usually diagnosed in infancy and childhood. The most common congenital neck mass is the thyroglossal duct cyst. The diagnosis is easily established from the presence of a cystic lesion in the anterior midline portion of the neck. The vast majority of branchial cleft cysts arise from the second branchial cleft. They can occur anywhere from the oropharyngeal tonsillar fossa to the supraclavicular region of the neck. Cystic hygroma is the most common form of lymphangioma. In the neck, cystic hygromas are most commonly found in the posterior cervical space. They typically extend into adjacent structures without respecting the fascial planes. Dermoid and epidermoid cysts result from sequestration of ectodermal tissue. The floor of the mouth is the most common location in the neck. Cervical thymic cysts are very uncommon lesions and are found anywhere from the angle of the mandible down to the sternum. Laryngoceles are classified into internal, external, and mixed types and have a frequent association with laryngeal carcinoma.
Index Terms: Dermoid, 20.366 • Head and neck neoplasms, 20.1471, 20.1473, 20.362, 20.366, 275.3154, 275.3156 • Hygroma, cystic, 20.362 • Neoplasms, in infants and children, 20.1471, 20.1473, 20.362, 20.366, 275.3154, 275.3156 • Thymus, cysts, 275.3154
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INTRODUCTION
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Congenital cystic masses of the neck include thyroglossal duct cysts, branchial cleft cysts, cystic hygromas, dermoid and epidermoid cysts, thymic and bronchogenic cysts (visceral cysts), and laryngoceles. These lesions vary in prevalence from common (thyroglossal duct cysts, branchial cleft cysts, and cystic hygromas) to very rare (thymic and cervical bronchogenic cysts). The absolute number remains unknown.
The clinical history and physical examination of the patient are the most important factors in the evaluation of a congenital neck mass. An appropriate knowledge of the embryology and anatomy of the cervical region frequently allows the differential diagnosis to be narrowed. The clinical features and usual locations of the most common congenital cystic lesions of the neck are summarized in the Table.
The evaluation of a patient suspected of having a congenital cervical cystic mass should follow an orderly progression. Because most congenital lesions manifest during infancy and early childhood, the patient's age provides important diagnostic information. Congenital cervical cystic lesions are usually slow-growing masses and typically cause symptoms only because of enlargement or infection. A painless soft or fluctuant cervical mass is the first clinical manifestation in most cases. Following physical examination, ultrasonography (US) is usually performed. US helps define the size and extent of the mass, demonstrate its relationship to surrounding normal structures, and confirm the cystic nature of the lesion. Computed tomography (CT) also provides this information and is ideally suited for evaluation of soft-tissue planes adjacent to larger masses that cannot be entirely visualized with US. Moreover, CT is superior for detecting calcification and, when contrast material is administered, the vascularity of lesions. Magnetic resonance (MR) imaging, with its multiplanar capability and superior contrast resolution, demonstrates the full extent of the mass and gives important supplemental information for accurate preoperative planning. This can be especially relevant in cases of extension into the mediastinum or deep spaces of the neck. Furthermore, MR imaging offers superior resolution for evaluating masses located in anatomically complex areas, such as the floor of the mouth.
The purpose of this article is to present the clinical, pathologic, and radiologic features of the most common congenital cystic lesions of the neck, emphasizing their embryologic origin.
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THYROGLOSSAL DUCT CYST
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The thyroid gland begins to develop in the 3rd week of fetal life as a median outgrowth from the floor of the primitive pharynx. This thyroid primordium originates at the level of the foramen cecum, which in the adult lies at the junction of the anterior two-thirds and posterior one-third of the tongue. The primitive thyroid descends in the neck, penetrates through the underlying mesoderm of the tongue and floor of the mouth musculature, and eventually passes anterior to the developing hyoid bone and laryngeal cartilages. The anlage of the gland reaches its final position in the inferior part of the neck by the 7th week of gestation after descending anterior to the thyrohyoid membrane and the strap muscles (sternothyroid and sternohyoid muscles) (1).
During its migration, the anlage of the thyroid gland is connected to the tongue by a narrow tubular structure, the thyroglossal duct. This duct normally involutes by the 8th–10th gestational week. The site of the original opening of the thyroglossal duct persists as the foramen cecum of the tongue, with the inferior end of the canal becoming the pyramidal lobe of the thyroid gland (1–3). If any portion of the thyroglossal duct persists, secretions from the epithelial lining (likely secondary to repeated local infection and inflammation) may give rise to cystic lesions (4). The duct is intimately associated with the developing hyoid bone, usually passing through it (Fig 1) (6). As a consequence, most thyroglossal duct cysts are found either at the level of the hyoid bone (15% of cases) or in the strap muscles (65%) immediately inferior.
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Figure 1. Pathway of the thyroglossal duct. Drawing shows a lateral view of the embryologic thyroglossal duct from the foramen cecum through the developing hyoid bone to the pyramidal lobe of the thyroid. If the duct fails to involute completely, a thyroglossal duct cyst may result, with 80% of these lesions being at or below the level of the hyoid bone. (Reprinted, with permission, from reference 5.)
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The thyroglossal duct cyst is the most common congenital neck mass, accounting for 70% of congenital neck anomalies (4), and the second most common benign neck mass, after benign lymphadenopathy (7). About 50% of patients present before 20 years of age, with a second group of patients presenting in young adulthood (5,8). No gender predilection has been reported (4). Rare cases of hereditary thyroglossal duct cysts have been reported; typically, these cysts have an autosomal dominant pattern of transmission and occur in prepubertal girls (9).
Clinical Characteristics
Thyroglossal duct cysts are located in the midline (75% of cases) or slightly off-midline (25%) in the anterior neck. They are always within 2 cm of the midline (10). Of those in a paramedian location, most will occur on the left for reasons that are not well understood (11). Approximately 80% of the cysts are located either at or below the level of the hyoid bone. The remaining 20% are located above the hyoid bone. Rarely, a thyroglossal duct cyst may manifest as a mass in the floor of the mouth (3,12–15).
Most authorities ascribe inflammation as the most likely cause for a thyroglossal duct cyst. The frequency of infections in childhood may explain the increased prevalence of these cysts in this age group (4).
A thyroglossal duct cyst usually manifests as an enlarging, painless mass in a pediatric or young adult patient. The duct and cyst characteristically move upward with tongue protrusion, a reflection of the origin of the duct at the foramen cecum (6,10,16). The size of the cyst ranges from 0.5 to 6 cm in diameter, but most are between 1.5 and 3 cm (17). Many patients with thyroglossal duct cysts present clinically as a consequence of infection (17). Despite initial improvement with antibiotic therapy, the cyst frequently recurs after the antibiotic course is completed (17).
About 1% of thyroglossal duct abnormalities are associated with thyroid carcinoma arising from ectopic rests of thyroid tissue within the duct and not from the duct itself. Although most (80%) of these tumors are of the papillary type, virtually every type of thyroid malignancy has been reported in association with thyroglossal duct cysts (4,10,18–21). The presence of a carcinoma within a thyroglossal duct cyst is rarely suspected preoperatively (4). Nodal spread is much less common in these thyroglossal duct cyst neoplasms than in primary carcinomas arising in the thyroid gland itself (4).
Simple incision and drainage or partial resection of a thyroglossal duct cyst virtually always leads to recurrence (Fig 2). Therefore, complete excision of the cyst with the Sistrunk procedure is the recommended surgical approach. This operation involves resection of the central portion of the hyoid bone and a core of tissue following the expected course of the thyroglossal duct to the foramen cecum (4). The recurrence rate following this procedure is 2.6%, which is much lower than the recurrence rate when incomplete excision is performed (up to 38%) (15,17).
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Figure 2a. Persistent thyroglossal duct sinus tract in a 5-year-old boy who had undergone two partial resections for a thyroglossal duct cyst in the preceding 9 months. (a) Photograph of the lower neck shows a fistulous ostium with a transverse surgical scar on both sides. (b) CT scan obtained after ethiodized oil was injected into the fistula shows focal collection of the contrast agent in the region of the foramen cecum (arrow). (c, d) CT scans obtained at lower levels show the contrast material–enhanced path of the thyroglossal duct along the anterior surface of the hyoid bone (arrow in c) and inferiorly to the skin ostium near the pyramidal lobe of the thyroid (arrow in d). (e) Photograph of the surgical specimen reveals entire length of the fistulous tract.
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Figure 2b. Persistent thyroglossal duct sinus tract in a 5-year-old boy who had undergone two partial resections for a thyroglossal duct cyst in the preceding 9 months. (a) Photograph of the lower neck shows a fistulous ostium with a transverse surgical scar on both sides. (b) CT scan obtained after ethiodized oil was injected into the fistula shows focal collection of the contrast agent in the region of the foramen cecum (arrow). (c, d) CT scans obtained at lower levels show the contrast material–enhanced path of the thyroglossal duct along the anterior surface of the hyoid bone (arrow in c) and inferiorly to the skin ostium near the pyramidal lobe of the thyroid (arrow in d). (e) Photograph of the surgical specimen reveals entire length of the fistulous tract.
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Figure 2c. Persistent thyroglossal duct sinus tract in a 5-year-old boy who had undergone two partial resections for a thyroglossal duct cyst in the preceding 9 months. (a) Photograph of the lower neck shows a fistulous ostium with a transverse surgical scar on both sides. (b) CT scan obtained after ethiodized oil was injected into the fistula shows focal collection of the contrast agent in the region of the foramen cecum (arrow). (c, d) CT scans obtained at lower levels show the contrast material–enhanced path of the thyroglossal duct along the anterior surface of the hyoid bone (arrow in c) and inferiorly to the skin ostium near the pyramidal lobe of the thyroid (arrow in d). (e) Photograph of the surgical specimen reveals entire length of the fistulous tract.
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Figure 2d. Persistent thyroglossal duct sinus tract in a 5-year-old boy who had undergone two partial resections for a thyroglossal duct cyst in the preceding 9 months. (a) Photograph of the lower neck shows a fistulous ostium with a transverse surgical scar on both sides. (b) CT scan obtained after ethiodized oil was injected into the fistula shows focal collection of the contrast agent in the region of the foramen cecum (arrow). (c, d) CT scans obtained at lower levels show the contrast material–enhanced path of the thyroglossal duct along the anterior surface of the hyoid bone (arrow in c) and inferiorly to the skin ostium near the pyramidal lobe of the thyroid (arrow in d). (e) Photograph of the surgical specimen reveals entire length of the fistulous tract.
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Figure 2e. Persistent thyroglossal duct sinus tract in a 5-year-old boy who had undergone two partial resections for a thyroglossal duct cyst in the preceding 9 months. (a) Photograph of the lower neck shows a fistulous ostium with a transverse surgical scar on both sides. (b) CT scan obtained after ethiodized oil was injected into the fistula shows focal collection of the contrast agent in the region of the foramen cecum (arrow). (c, d) CT scans obtained at lower levels show the contrast material–enhanced path of the thyroglossal duct along the anterior surface of the hyoid bone (arrow in c) and inferiorly to the skin ostium near the pyramidal lobe of the thyroid (arrow in d). (e) Photograph of the surgical specimen reveals entire length of the fistulous tract.
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Pathologic Characteristics
Thyroglossal duct cysts contain a colorless, viscous secretion. At histologic examination, stratified squamous epithelium or ciliated pseudostratified columnar epithelium lining the cyst wall is usually seen (16). Mucous glands may also be present (10). Ectopic thyroid tissue along the course of the duct is variably reported in up to 62% of cases (Fig 3) (19,20,22). LiVolsi et al (22) speculated that the variation in detection of this tissue was a reflection of the degree of meticulous examination by the reviewing pathologist.
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Figure 3. Photomicrograph (original magnification, x4; hematoxylin-eosin [H-E] stain) of a thyroglossal duct cyst specimen shows squamous epithelium (arrowheads). The cysts may also be lined with respiratory epithelium. Most (about 60%) of these lesions contain some remnant of thyroid tissue (arrows).
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Radiologic Features
On all radiologic images, a thyroglossal duct cyst manifests as a cystlike mass either in the midline of the anterior neck at the level of the hyoid bone or within the strap muscles just off the midline.
At US, the finding of an anechoic mass with a thin outer wall in this characteristic location easily establishes the diagnosis of a thyroglossal duct cyst. However, this "classic" appearance is seen in less than half (42%) of the cases. More commonly, these cysts manifest as hypoechoic masses, often with increased through-transmission. They may be either homogeneous or heterogeneous in appearance with variable degrees of fine to coarse internal echoes. There is no correlation between the sonographic appearance and pathologic evidence of infection and inflammation (23). Heterogeneity seen in thyroglossal duct cysts on sonograms is more likely due to the proteinaceous content of the fluid secreted from the cyst wall rather than to infection (23). Preoperative sonographic visualization of normal thyroid tissue is sufficient to exclude a diagnosis of ectopic thyroid tissue and obviates routine thyroid scintigraphy (24).
On CT scans, a thyroglossal duct cyst usually appears as a smooth, well-circumscribed mass anywhere along the vertical course of the vestigial thyroglossal duct (Figs 4–6). The mass has a thin wall and homogeneous attenuation, the values of which correspond to those of fluid (10–18 HU). Elevated attenuation values of the fluid cyst reflect its increased protein content and generally correlate with a history of prior infections. Although thyroglossal duct cysts are usually unilocular, septations may be seen occasionally. Peripheral rim enhancement is usually observed on contrast-enhanced scans (3).
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Figure 4a. Thyroglossal duct cyst in a 41-year-old man. (a, b) Axial contrast-enhanced CT scans show a cystic mass in the anterior midline of the neck just above (a) and at the level of (b) the hyoid bone. (c) Axial T1-weighted MR image at the thyrohyoid membrane level shows hyperintensity of the mass, a finding suggestive of proteinaceous content or hemorrhage.
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Figure 4b. Thyroglossal duct cyst in a 41-year-old man. (a, b) Axial contrast-enhanced CT scans show a cystic mass in the anterior midline of the neck just above (a) and at the level of (b) the hyoid bone. (c) Axial T1-weighted MR image at the thyrohyoid membrane level shows hyperintensity of the mass, a finding suggestive of proteinaceous content or hemorrhage.
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Figure 4c. Thyroglossal duct cyst in a 41-year-old man. (a, b) Axial contrast-enhanced CT scans show a cystic mass in the anterior midline of the neck just above (a) and at the level of (b) the hyoid bone. (c) Axial T1-weighted MR image at the thyrohyoid membrane level shows hyperintensity of the mass, a finding suggestive of proteinaceous content or hemorrhage.
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Figure 6a. Figures 5, 6. (5) Thyroglossal duct cyst in a 39-year-old man. Contrast-enhanced CT scan shows a hypoattenuated mass (m) in the right strap muscles. (Courtesy of the Department of Radiology, Neuroradiology Section, University of California at San Francisco.) (6) Thyroglossal duct cyst in a 71-year-old man with a 1-year history of progressive swelling on the left side of the neck. (a) Contrast-enhanced CT scan shows a large cystic mass arising from the left strap muscles. (b) Photograph of the cut specimen shows the smooth inner lining and roughened exterior surface of the cyst.
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Figure 6b. Figures 5, 6. (5) Thyroglossal duct cyst in a 39-year-old man. Contrast-enhanced CT scan shows a hypoattenuated mass (m) in the right strap muscles. (Courtesy of the Department of Radiology, Neuroradiology Section, University of California at San Francisco.) (6) Thyroglossal duct cyst in a 71-year-old man with a 1-year history of progressive swelling on the left side of the neck. (a) Contrast-enhanced CT scan shows a large cystic mass arising from the left strap muscles. (b) Photograph of the cut specimen shows the smooth inner lining and roughened exterior surface of the cyst.
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An uncomplicated thyroglossal duct cyst has low signal intensity on T1-weighted images and is hyperintense on T2-weighted images, findings that reflect its fluid content. The rim will be nonenhancing unless inflammation is present (25). In case of infection or hemorrhage, a thick irregular rim may be visualized, and the signal intensity of the fluid becomes variable from the presence of proteinaceous debris (Fig 4).
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BRANCHIAL CLEFT ANOMALIES
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By the end of the 4th week of embryonic life, the branchial arches (derived from neural crest cells) and the mesenchyme (derived from the lateral mesoderm) are easily recognizable. Five pairs of ectodermal clefts (grooves) and five endodermal branchial pouches separate the six arches, with a closing membrane located at the interface between the pouches and the clefts (1,2).
The first branchial cleft normally gives rise to the eustachian tube, tympanic cavity, and mastoid antrum and contributes to the formation of the tympanic membrane. It is the only cleft to contribute to an adult structure, the external auditory canal. The second, third, and fourth branchial clefts are part of an ectodermally lined depression known as the cervical sinus of His. As the second and fifth branchial clefts merge with each other, this cervical sinus is obliterated. The second branchial pouch, lined by endoderm, gives rise to the palatine tonsil and tonsillar fossa. The third branchial pouch forms the inferior parathyroid gland, thymus, and pyriform sinus; the fourth branchial pouch leads to the formation of the superior parathyroid gland and apex of the pyriform sinus (Fig 7) (1).
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Figure 7. Branchial apparatus. Diagram illustrates the developing branchial apparatus. The branchial clefts (or grooves) are ectodermal lined, whereas the pharyngeal pouches are of endodermal origin. The branchial arches are mesodermal in nature. The second branchial arch begins to overgrow the third and fourth branchial arches to form the cervical sinus of His. In normal development, the sinus is obliterated when the second branchial arch merges with the epicardial ridge. (Reprinted, with permission, from reference 26.)
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The pathogenesis of branchial cleft anomalies remains controversial. Most authorities believe that they arise from incomplete obliteration of the cervical sinus of His or from buried epithelial cell rests (27). They manifest as any combination of sinus, fistula, or cyst. Sinuses almost always open externally on the side of the neck, whereas a fistula manifests as a patent abnormal canal, opening externally on the neck surface and internally within the pharyngeal mucosa (8). In a review of 274 patients with branchial cleft anomalies at the Mayo Clinic, Telander and Deane (8) reported that most of the anomalies (75%) were cysts; 25%, fistulas; and 1%, skin tags and cartilages. Patients with branchial cleft cysts are usually older children or young adults in contrast to patients with fistulas, who are usually infants or young children (8,28). Bilateral branchial cleft anomalies are reported to occur in 2%–3% of cases and are often familial (29).
First Branchial Cleft Cyst
A first branchial cleft cyst, or parotid lymphoepithelial cyst, arises along the residual embryologic tract of the first branchial cleft or arch extending from the external auditory canal through the parotid gland to the submandibular triangle. These cysts account for only 5%–8% of all branchial cleft defects (30) and are most commonly seen in middle-aged women (31).
Clinical Characteristics.—Cysts of the first branchial cleft usually manifest as recurrent abscesses or other inflammation (sinus tract) either around the ear or at the angle of the mandible. The patient typically has a history of recurrent parotid abscesses unresponsive to antibiotic therapy and drainage. Otorrhea commonly occurs if the cyst drains into the external auditory canal. Occasionally, a sinus tract extending to the hyoid bone may be seen. These cystic anomalies often mimic the clinical characteristics of parotid neoplasms and may even be associated with facial nerve palsy (8). Both children and adults may be affected (32,33). Complete surgical excision is the only curative therapy for these lesions (32,33).
Pathologic Characteristics.—Work (32) divided first branchial cleft cysts into two types based on embryologic criteria. The Work type I cyst is derived from ectoderm and represents a duplication anomaly of the membranous external auditory canal from the first branchial cleft. It is characteristically found medial to the concha of the ear in a parallel course with the external auditory canal but may extend into the retroauricular area. It is lined with squamous epithelium. No skin appendages are seen in Work type I cysts (32,33).
Work type II cysts arise from the first branchial cleft and arch with a possible contribution from the second branchial arch. Consequently, they are derived from ectoderm and mesoderm. They involve both the external auditory canal and cartilaginous pinna. The presence of skin appendages (hair follicles, sweat and sebaceous glands) contained in the squamous epithelial lining of these cysts allows the pathologist to distinguish Work type II cysts from type I cysts. Both types produce keratin from the squamous epithelium lining (32,33).
The first branchial cleft cysts associated with the parotid gland are classified most often as Work type II cysts because both ectodermal and mesodermal elements are present on histologic examination. They are usually distinguished from the more common lymphoepithelial cysts of the parotid gland, which lack mesodermal components (34).
Radiologic Features.—On CT scans, a first branchial cleft cyst appears as a cystic mass either within, superficial to, or deep to the parotid gland. Cyst wall thickness and enhancement are variable and increase with recurrent infections.
In most cases, neither the CT nor MR imaging appearance of these cysts is characteristic enough to allow differentiating a first branchial cleft cyst from any other cystic mass of the parotid gland. As with any lesion of the deep margin of the parotid gland, a first branchial cleft cyst in this location may extend into the adjacent fat-containing parapharyngeal space.
Second Branchial Cleft Cyst
The vast majority (95%) of branchial cleft anomalies arise from the second cleft (14). At least three-fourths of these anomalies are cysts (10), which typically occur between 10 and 40 years of age, in contrast to fistulas or sinuses, which manifest most commonly during the 1st decade of life (21,35). No gender predilection has been reported (31).
Bailey (36) classified second branchial cleft cysts into four types. The Bailey type I cyst is the most superficial and lies along the anterior surface of the sternocleidomastoid muscle, just deep to the platysma muscle. The type II cyst is the most common and found in the "classic" location for these cysts: along the anterior surface of the sternocleidomastoid muscle, lateral to the carotid space, and posterior to the submandibular gland. A type III cyst extends medially between the bifurcation of the internal and external carotid arteries to the lateral pharyngeal wall. The type IV cyst lies in the pharyngeal mucosal space and is lined with columnar epithelium (36). Figure 8 outlines the path of the second branchial cleft tract in the neck.
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Figure 8. Second branchial cleft tract. Drawing shows the path of second branchial cleft anomalies, which can occur anywhere along a line from the supraclavicular region to the oropharyngeal mucosa. The path travels lateral to the common carotid artery, then heads medially between the external carotid (EC) and internal carotid (IC) arteries under the glossopharyngeal nerve (IX) and above the hypoglossal nerve (XII). If the tract continues further along this course, it will enter the parapharyngeal space and pierce the middle constrictor muscle before ending as an opening within the tonsillar fossa. (Reprinted, with permission, from reference 5.)
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Clinical Characteristics.—Most second branchial cleft cysts are located in the submandibular space. However, because of the anatomic relationship of the second branchial apparatus and the cervical sinus, they can occur anywhere along a line from the oropharyngeal tonsillar fossa to the supraclavicular region of the neck (30).
These cysts usually appear as painless, fluctuant masses in the lateral portion of the neck adjacent to the anteromedial border of the sternocleidomastoid muscle at the mandibular angle (13,21,37). The mass enlarges slowly over time and may become painful and tender if secondarily infected (21). In a young patient, a history of recurrent inflammation in the region of the mandibular angle is highly suggestive of a second branchial cleft cyst. If a fistula is present, the ostium is usually noted at birth just above the clavicle in the anterior neck (5).
Surgical excision is the recommended therapy for a branchial cleft anomaly because of the increased frequency of secondary infection (8).
Pathologic Characteristics.—Second branchial cleft cysts range in size from 1 to 10 cm (10,17). They are usually filled with a turbid, yellowish fluid that may contain cholesterol crystals. Their walls are thin and lined with stratified squamous epithelium overlying lymphoid tissue (17,21,37). Columnar respiratory epithelium is occasionally present (Fig 9).
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Figure 9. Photomicrograph (original magnification, x10; H-E stain) of a branchial cleft cyst specimen shows lining of stratified squamous epithelium (arrowheads). The cyst wall usually contains a diffuse or nodular lymphoid component, often with germinal centers (arrow). The absence of sinusoids and a subcapsular sinus distinguishes this from a lymph node.
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Histologic specimens treated with immunohistochemical stains show mural lymphatic sinuses with the mantle zones of the follicles always aligned toward the epithelium. This orientation is analogous to that of the normal crypt epithelium of the palatine tonsils and marginal sinuses in lymph nodes (38).
Radiologic Features.—At US, a second branchial cleft cyst is seen as a sharply marginated, round to ovoid, centrally anechoic mass with a thin peripheral wall that displaces the surrounding soft tissues. The mass is compressible and shows distinct acoustic enhancement. Occasionally, fine, indistinct internal echoes, representing debris, may be seen.
At CT, these cysts are typically well-circumscribed, homogeneously hypoattenuated masses surrounded by a uniformly thin wall (37). The mural thickness may increase after infection. The "classic" location of these cysts (at either CT or MR imaging) is at the anteromedial border of the sternocleidomastoid muscle, lateral to the carotid space, and at the posterior margin of the submandibular gland. The cyst typically displaces the sternocleidomastoid muscle posteriorly or posterolaterally, pushes the vessels of the carotid space medially or posteromedially, and displaces the submandibular gland anteriorly (Figs 10, 11) (13,30). It may also be seen more medially within the parapharyngeal space after extending through the stylomandibular tunnel and middle constrictor muscle (Fig 12) (1,39).
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Figure 10a. Second branchial cleft cyst in a 30-year-old woman with a 14-month history of a mass in the left side of the neck that was unresponsive to antibiotics and that enlarged somewhat the month before surgery. (a) Axial T1-weighted image shows a well-defined mass (m) along the anterior border of the left sternocleidomastoid muscle (arrowhead), lateral to the carotid space (white arrow), and posterior to the submandibular gland (black arrow)—the classic location for a second branchial cleft cyst. Increased signal intensity of the mass is due to either proteinaceous debris or prior hemorrhage. (b) Axial T2-weighted image reveals moderate to marked hypointensity of the mass (m), consistent with accumulation of proteinaceous debris or hemorrhage. (c) Coronal contrast-enhanced T1-weighted image with fat suppression shows mild rim enhancement of the mass (m). (d) Intraoperative photograph shows the mass and sternocleidomastoid muscle outlined in ink on the skin surface. (e) Photograph of the surgical specimen shows the well-circumscribed mass with mildly lobulated contours.
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Figure 10b. Second branchial cleft cyst in a 30-year-old woman with a 14-month history of a mass in the left side of the neck that was unresponsive to antibiotics and that enlarged somewhat the month before surgery. (a) Axial T1-weighted image shows a well-defined mass (m) along the anterior border of the left sternocleidomastoid muscle (arrowhead), lateral to the carotid space (white arrow), and posterior to the submandibular gland (black arrow)—the classic location for a second branchial cleft cyst. Increased signal intensity of the mass is due to either proteinaceous debris or prior hemorrhage. (b) Axial T2-weighted image reveals moderate to marked hypointensity of the mass (m), consistent with accumulation of proteinaceous debris or hemorrhage. (c) Coronal contrast-enhanced T1-weighted image with fat suppression shows mild rim enhancement of the mass (m). (d) Intraoperative photograph shows the mass and sternocleidomastoid muscle outlined in ink on the skin surface. (e) Photograph of the surgical specimen shows the well-circumscribed mass with mildly lobulated contours.
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Figure 10c. Second branchial cleft cyst in a 30-year-old woman with a 14-month history of a mass in the left side of the neck that was unresponsive to antibiotics and that enlarged somewhat the month before surgery. (a) Axial T1-weighted image shows a well-defined mass (m) along the anterior border of the left sternocleidomastoid muscle (arrowhead), lateral to the carotid space (white arrow), and posterior to the submandibular gland (black arrow)—the classic location for a second branchial cleft cyst. Increased signal intensity of the mass is due to either proteinaceous debris or prior hemorrhage. (b) Axial T2-weighted image reveals moderate to marked hypointensity of the mass (m), consistent with accumulation of proteinaceous debris or hemorrhage. (c) Coronal contrast-enhanced T1-weighted image with fat suppression shows mild rim enhancement of the mass (m). (d) Intraoperative photograph shows the mass and sternocleidomastoid muscle outlined in ink on the skin surface. (e) Photograph of the surgical specimen shows the well-circumscribed mass with mildly lobulated contours.
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Figure 10d. Second branchial cleft cyst in a 30-year-old woman with a 14-month history of a mass in the left side of the neck that was unresponsive to antibiotics and that enlarged somewhat the month before surgery. (a) Axial T1-weighted image shows a well-defined mass (m) along the anterior border of the left sternocleidomastoid muscle (arrowhead), lateral to the carotid space (white arrow), and posterior to the submandibular gland (black arrow)—the classic location for a second branchial cleft cyst. Increased signal intensity of the mass is due to either proteinaceous debris or prior hemorrhage. (b) Axial T2-weighted image reveals moderate to marked hypointensity of the mass (m), consistent with accumulation of proteinaceous debris or hemorrhage. (c) Coronal contrast-enhanced T1-weighted image with fat suppression shows mild rim enhancement of the mass (m). (d) Intraoperative photograph shows the mass and sternocleidomastoid muscle outlined in ink on the skin surface. (e) Photograph of the surgical specimen shows the well-circumscribed mass with mildly lobulated contours.
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Figure 10e. Second branchial cleft cyst in a 30-year-old woman with a 14-month history of a mass in the left side of the neck that was unresponsive to antibiotics and that enlarged somewhat the month before surgery. (a) Axial T1-weighted image shows a well-defined mass (m) along the anterior border of the left sternocleidomastoid muscle (arrowhead), lateral to the carotid space (white arrow), and posterior to the submandibular gland (black arrow)—the classic location for a second branchial cleft cyst. Increased signal intensity of the mass is due to either proteinaceous debris or prior hemorrhage. (b) Axial T2-weighted image reveals moderate to marked hypointensity of the mass (m), consistent with accumulation of proteinaceous debris or hemorrhage. (c) Coronal contrast-enhanced T1-weighted image with fat suppression shows mild rim enhancement of the mass (m). (d) Intraoperative photograph shows the mass and sternocleidomastoid muscle outlined in ink on the skin surface. (e) Photograph of the surgical specimen shows the well-circumscribed mass with mildly lobulated contours.
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Figure 11a. Figures 11, 12. (11) Second branchial cleft cyst in an 11-year-old boy with a mass in the right side of the neck and a history of recurrent inflammation. (a) Axial gadolinium-enhanced T1-weighted MR image shows a hypointense mass in the right side of the neck in the classic location for a second branchial cleft cyst. Irregular inner border of the mass suggests an associated inflammatory process. (b) Coronal T1-weighted MR image shows the mass at the inferior margin of the right parotid gland and lateral to carotid vessels. (c) Photograph of the resected specimen shows the thick capsule of the cystic lesion filled with keratinaceous debris. (12) Second branchial cleft cyst in a 29-year-old woman with a 1-month history of dysphagia, otalgia of the right ear, and swelling of the right side of the neck. Contrast-enhanced CT scan shows a well-defined, right-sided neck mass (m) deep to the carotid space and with medial extension toward the oropharynx.
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Figure 11b. Figures 11, 12. (11) Second branchial cleft cyst in an 11-year-old boy with a mass in the right side of the neck and a history of recurrent inflammation. (a) Axial gadolinium-enhanced T1-weighted MR image shows a hypointense mass in the right side of the neck in the classic location for a second branchial cleft cyst. Irregular inner border of the mass suggests an associated inflammatory process. (b) Coronal T1-weighted MR image shows the mass at the inferior margin of the right parotid gland and lateral to carotid vessels. (c) Photograph of the resected specimen shows the thick capsule of the cystic lesion filled with keratinaceous debris. (12) Second branchial cleft cyst in a 29-year-old woman with a 1-month history of dysphagia, otalgia of the right ear, and swelling of the right side of the neck. Contrast-enhanced CT scan shows a well-defined, right-sided neck mass (m) deep to the carotid space and with medial extension toward the oropharynx.
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Figure 11c. Figures 11, 12. (11) Second branchial cleft cyst in an 11-year-old boy with a mass in the right side of the neck and a history of recurrent inflammation. (a) Axial gadolinium-enhanced T1-weighted MR image shows a hypointense mass in the right side of the neck in the classic location for a second branchial cleft cyst. Irregular inner border of the mass suggests an associated inflammatory process. (b) Coronal T1-weighted MR image shows the mass at the inferior margin of the right parotid gland and lateral to carotid vessels. (c) Photograph of the resected specimen shows the thick capsule of the cystic lesion filled with keratinaceous debris. (12) Second branchial cleft cyst in a 29-year-old woman with a 1-month history of dysphagia, otalgia of the right ear, and swelling of the right side of the neck. Contrast-enhanced CT scan shows a well-defined, right-sided neck mass (m) deep to the carotid space and with medial extension toward the oropharynx.
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Figure 12. Figures 11, 12. (11) Second branchial cleft cyst in an 11-year-old boy with a mass in the right side of the neck and a history of recurrent inflammation. (a) Axial gadolinium-enhanced T1-weighted MR image shows a hypointense mass in the right side of the neck in the classic location for a second branchial cleft cyst. Irregular inner border of the mass suggests an associated inflammatory process. (b) Coronal T1-weighted MR image shows the mass at the inferior margin of the right parotid gland and lateral to carotid vessels. (c) Photograph of the resected specimen shows the thick capsule of the cystic lesion filled with keratinaceous debris. (12) Second branchial cleft cyst in a 29-year-old woman with a 1-month history of dysphagia, otalgia of the right ear, and swelling of the right side of the neck. Contrast-enhanced CT scan shows a well-defined, right-sided neck mass (m) deep to the carotid space and with medial extension toward the oropharynx.
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MR imaging better depicts the deep tissue extent of a second branchial cleft cyst, which allows accurate preoperative planning. The cyst fluid varies from hypointense to slightly hyperintense relative to muscle on T1-weighted images and is usually hyperintense on T2-weighted images (31). Mural thickness and enhancement vary, depending of the presence and severity of any associated inflammatory process (Fig 11) (30).
Occasionally, a "beak sign" may be seen on axial CT or MR images. This sign represents a curved rim of tissue or "beak" pointing medially between the internal and external carotid arteries. It is considered a pathognomonic imaging feature of a second branchial cleft cyst, specifically a Bailey type III cyst (5).
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THIRD AND FOURTH BRANCHIAL CLEFT CYSTS
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Cysts arising from the third and fourth branchial clefts are extremely rare, with only a few cases reported (27,40). These lesions have been described in children and young adults (6). Despite their rarity, third branchial cleft cysts constitute the second most common congenital lesion of the posterior cervical space of the neck after cystic hygroma (41). Anomalies of the fourth branchial cleft usually manifest as a sinus tract rather than a cyst or fistula. The vast majority of these lesions occur on the left side; of 31 cases reported, 28 have been on the left (40).
By definition, a third branchial cleft cyst must lie posterior to the common or internal carotid artery, between the hypoglossal nerve below and the glossopharyngeal nerve above. If the lesion is a complete fistula, it will pierce the thyrohyoid membrane in its course to the pyriform sinus. Most of these cysts are located in the posterior cervical space posterior to the sternocleidomastoid muscle (27).
A fourth branchial cleft sinus tract, following its embryologic derivation, arises from the pyriform sinus, pierces the thyrohyoid membrane, and begins a descent into the mediastinum, following the path of the tracheoesophageal groove. If the tract is long enough, a left-sided lesion will eventually travel under the aortic arch (or, in the rare case of a right-sided lesion, under the right subclavian artery) before ascending into the neck along the ventral surface of the common carotid artery (27). Most of these lesions are short and thus sinus tracts. Presumably because of the length of this branchial cleft, a complete fourth branchial cleft fistula has not been reported (40).
Distinguishing third branchial cleft anomalies from fourth branchial cleft anomalies may be difficult, since both have relationships with the pyriform sinus. The difference between the two lesions lies in their relationships to the superior laryngeal nerve. Those above this structure are of third branchial cleft origin, whereas those below are derived from the fourth branchial cleft (40).
An ectopic or undescended parathyroid gland may be associated with either lesion, since the parathyroid glands arise from the third and fourth branchial pouches (1). Not surprisingly, parathyroid adenomas have also been reported in association with branchial cleft cysts (42).
Clinical Characteristics.—As with other branchial cleft cysts, a third branchial cleft cyst usually manifests as a painless, fluctuant mass in the posterior triangle area of the neck. Like a cystic hygroma (lymphangioma), the mass often distends during a viral infection of the upper respiratory tract. Surgical excision is the recommended therapy of choice for these lesions because of the increased frequency of secondary infection (8).
Radiologic Characteristics.—A third branchial cleft cyst most commonly appears as a unilocular cystic mass centered in the posterior cervical space on CT and MR images. As with other branchial cleft cysts, the cyst fluid may vary in signal intensity on T1-weighted images depending on the protein concentration and is typically hyperintense relative to muscle on T2-weighted images (31). Benson et al (27) reported a fourth branchial cleft cyst that connected with the pyriform sinus and appeared similar to an external or mixed laryngocele.
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CYSTIC HYGROMA
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A cystic hygroma is the most common form of lymphangioma and constitutes about 5% of all benign tumors of infancy and childhood (41). The overwhelming majority (about 80%–90%) are detected by the time the patient is 2 years old, the age of greatest lymphatic growth (21,43). Only a few cases have been reported in adults (5,44). No gender predilection has been reported (45).
Cystic hygroma is thought to arise from an early sequestration of embryonic lymphatic channels, as suggested by Dowd (46) in 1913 and expanded on by Goetch in 1938 (47). This sequestration apparently occurs more commonly in the developing jugular lymph sac pair than in the other four embryonic sites of the lymphatic system. From this location, the sequestered site follows the path of the surrounding mesenchyme destined for either the neck or the developing mediastinum. This accounts for the propensity of these lesions to occur in the lower neck, axilla, and upper mediastinum (48). Alternatively, a cystic hygroma may arise from a failure of the juguloaxillary lymphatic sac to drain into the internal jugular vein, producing a congenital obstruction of lymphatic drainage (7,25,49). Some authors have proposed that involution of a cystic hygroma in utero produces the "web neck" of Turner syndrome (45,50).
Clinical Characteristics
Approximately 75%–80% of all cystic hygromas involve the neck and the lower portion of the face. In children, the most common location is the posterior cervical space, followed by the oral cavity. In adults, cystic hygromas are more commonly seen in the sublingual, submandibular, and parotid spaces (5,44). Other reported locations include the axilla (20% of cases), the mediastinum (5%), the abdominal cavity (colon, spleen, and liver), the retroperitoneum (kidneys), the scrotum, and even the skeleton (37,45).
These lesions are characteristically infiltrative in nature and do not respect fascial planes. Consequently, they may extend inferiorly from the posterior cervical triangle into the axilla and mediastinum or anteriorly into the floor of the mouth and the tongue (41). If the mass is very large, it may extend across the midline (37,43). Only 3%–10% of cervical cystic hygromas are associated with extension into the mediastinum (21,43).
The majority of cystic hygromas are clinically asymptomatic and manifest as painless, soft or semifirm masses in the neck. Size is extremely variable. Very large masses may compromise the airway by extrinsic pressure resulting in death. To avoid this outcome, early tracheostomy is required (5). Although these masses usually grow slowly, they may suddenly increase in size secondary to hemorrhage or trauma or because of a viral infection when large amounts of lymphatic fluid are produced from the lymphoid follicles in the cyst wall (51). Other reported clinical manifestations include facial nerve paralysis, dysphagia, or other feeding problems (31). Chylothorax and chylopericardium may occur as complications of mediastinal involvement.
Pathologic Characteristics
Cystic hygromas are composed of multiple dilated cystic spaces separated by minimal intervening stroma. The cysts vary in diameter from a few millimeters to more than 10 cm, and most contain chylous fluid.
These thin-walled spaces are lined by endothelial cells and supporting connective tissue stroma (Fig 13) (10,37). Lesions may extend into adjacent soft tissues, invade into muscle, and surround vascular structures.
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Figure 13. Photomicrograph (original magnification, x1; H-E stain) of a cystic hygroma specimen shows multiple endothelium-lined vascular spaces. Several of the larger spaces (S) are indicated. The stroma includes fibrous tissue, adipose tissue, and aggregates of lymphoid cells (arrows).
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Currently, it is believed that cystic hygromas and the other three types of lymphangioma (cavernous lymphangioma, capillary or simple lymphangioma, and vasculolymphatic malformation) are manifestations of the same disease process. This theory is supported by the frequent observation of combinations of the four types within a single lesion at histologic examination. The differences in gross morphologic features of these four types may be explained by the nature of the stroma around the malformation. If loose connective tissue surrounds the lymphatic anomaly, a cystic hygroma is more likely to be seen. Conversely, if the surrounding tissue is firmer in texture, the other types of lymphangioma should be seen (45,52).
Radiologic Features
On US scans, most cystic hygromas manifest as a multilocular predominantly cystic mass with septa of variable thickness (53). The echogenic portions of the lesion correlate with clusters of small, abnormal lymphatic channels (53). Fluid-fluid levels can be observed with a characteristic echogenic, hemorrhagic component layering in the dependent portion of the lesion (54). Prenatal US may demonstrate a cystic hygroma in the posterior neck soft tissues (Fig 14) (50).
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Figure 14. Cystic hygroma. Intrauterine sonogram, obtained at 14 weeks gestation to evaluate vaginal bleeding, shows a large, multiseptated, anechoic mass (h) of the posterior neck.
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On CT images, cystic hygromas tend to appear as poorly circumscribed, multiloculated, hypoattenuated masses. They typically have characteristic homogeneous fluid attenuation (Figs 15, 16) (21,43). Infected lesions or those that have been in the past commonly show higher attenuation than that seen in simple fluid. Usually, the mass is centered in the posterior triangle or in the submandibular space (Figs 15, 17, 18). It is not uncommon for some of these lesions to extend from one space in the neck into another as a result of their infiltrative nature (Figs 17, 19) (21).
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Figure 15. Figures 15, 16. (15) Cystic hygroma in a 28-year-old man with a 4-week history of painless swelling of the left side of the neck unresponsive to antibiotics. Fine-needle aspiration yielded serous fluid. Contrast-enhanced CT scan shows a hypoattenuated mass (h) within the posterior cervical space deep to the sternocleidomastoid muscle. At surgery, the mass was adherent to the internal jugular vein. (Courtesy of the Department of Radiology, Naval Medical Center, San Diego, Calif.) (16) Cystic hygroma in a newborn boy. (a) Photograph shows a large bilobulated mass extending from the neck into the chest wall, axilla, and lower face. (b) Sagittal CT scan shows erosion of the mandible and invasion of the oral cavity. Multiple septa are seen.
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Figure 16a. Figures 15, 16. (15) Cystic hygroma in a 28-year-old man with a 4-week history of painless swelling of the left side of the neck unresponsive to antibiotics. Fine-needle aspiration yielded serous fluid. Contrast-enhanced CT scan shows a hypoattenuated mass (h) within the posterior cervical space deep to the sternocleidomastoid muscle. At surgery, the mass was adherent to the internal jugular vein. (Courtesy of the Department of Radiology, Naval Medical Center, San Diego, Calif.) (16) Cystic hygroma in a newborn boy. (a) Photograph shows a large bilobulated mass extending from the neck into the chest wall, axilla, and lower face. (b) Sagittal CT scan shows erosion of the mandible and invasion of the oral cavity. Multiple septa are seen.
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Figure 16b. Figures 15, 16. (15) Cystic hygroma in a 28-year-old man with a 4-week history of painless swelling of the left side of the neck unresponsive to antibiotics. Fine-needle aspiration yielded serous fluid. Contrast-enhanced CT scan shows a hypoattenuated mass (h) within the posterior cervical space deep to the sternocleidomastoid muscle. At surgery, the mass was adherent to the internal jugular vein. (Courtesy of the Department of Radiology, Naval Medical Center, San Diego, Calif.) (16) Cystic hygroma in a newborn boy. (a) Photograph shows a large bilobulated mass extending from the neck into the chest wall, axilla, and lower face. (b) Sagittal CT scan shows erosion of the mandible and invasion of the oral cavity. Multiple septa are seen.
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Figure 17a. Figures 17–19. (17) Cystic hygroma in a 20-month-old girl with swelling under the right jaw and neck noted by the mother. (a) Contrast-enhanced CT scan shows a large right-sided neck mass with fluid-fluid levels (arrows) indicative of recent hemorrhage. (b) Axial T1-weighted image shows heterogeneous signal intensity within the mass (m), which fills the right parotid space and portions of the mandibular space. Areas of hyperintensity correspond to regions of hemorrhage. (c) Coronal T1-weighted image shows extension of the mass into submandibular and sublingual spaces. (d) Photograph of the specimen shows the cystic lobules (arrows) of the multiloculated mass; cut surface (arrowheads) of a lobule reveals hemorrhage. (18) Cystic hygroma. Axial T1-weighted image shows a well-defined mass (m) within the right posterior cervical space that displaces the adjacent sternocleidomastoid muscle. (19) Cystic hygroma in a 36-year-old woman with a left-sided neck mass that enlarged during viral upper respiratory infections. Coronal T1-weighted image shows a large hypointense mass in the left side of the neck extending from the submandibular space to the thoracic inlet. Multiple septa (arrows) cross the lesion.
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Figure 17b. Figures 17–19. (17) Cystic hygroma in a 20-month-old girl with swelling under the right jaw and neck noted by the mother. (a) Contrast-enhanced CT scan shows a large right-sided neck mass with fluid-fluid levels (arrows) indicative of recent hemorrhage. (b) Axial T1-weighted image shows heterogeneous signal intensity within the mass (m), which fills the right parotid space and portions of the mandibular space. Areas of hyperintensity correspond to regi | |
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Abstract
INTRODUCTION
