Core Curriculum, The: Ultrasound
1st Edition

9
Thyroid, Parathyroid, and Neck Ultrasound
Sonography of the thyroid gland is one of the more frustrating areas of US imaging. Expectations are high because sonography is exquisitely sensitive to thyroid abnormalities. Unfortunately, US findings are rarely specific for any disease. Evaluation of thyroid nodules is particularly annoying because thyroid nodules are exceedingly common and US detects most of them, even as small as 1-2 mm, but can rarely unequivocally differentiate benign from malignant nodules. Most of the nodules detected by US are not clinically significant. Fortunately, thyroid cancer is relatively rare; so criteria can be selected to limit the number of biopsies performed and still diagnose the majority of clinically significant cancers. Sonographic guidance is used to direct aspiration biopsy of nonpalpable thyroid nodules and to guide procedures such as alcohol ablation of thyroid lesions [1,2,3].
US is utilized to detect parathyroid adenomas in patients with clinical hyperparathyroidism. These adenomas can then be removed surgically or ablated with US-guided, alcohol injection. Preoperative localization of adenomas decreases operative time and surgical morbidity. Sonography is limited by its inability to detect ectopic parathyroid adenomas in the mediastinum. These lesions may be demonstrated by Tc-99m sestamibi scans, CT or MR [4,5,6].
Masses and adenopathy can be accurately characterized by US, which can also be used to guide aspiration or biopsy.
Imaging Technique
US of the neck is performed with the patient in supine position. The neck is hyperextended by placement of a pillow or folded towels under the patient’s shoulders. A linear array transducer with frequency of 5-10 MHz is utilized. Occasionally, when the thyroid is greatly enlarged, curved-array or sector transducers are used to provide the “big picture.” Images are obtained in transverse and longitudinal planes. The lobes of the thyroid gland and any
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focal lesions are measured in three dimensions. Volumes are calculated using the standard formula for volume of an ellipsoid (length × width × height × 0.52). The neck is thoroughly examined for adenopathy. Intrathoracic extension of thyroid disease can be demonstrated by angling the US transducer downward into the mediastinum from a supra-manubrial position. Spectral, color, and power Doppler are utilized to demonstrate the vascularity of the thyroid gland and any focal lesions.
Figure 9.1 Normal Thyroid Anatomy. A transverse image through the mid-thyroid gland demonstrates normal sonographic landmarks. a, common carotid artery; i, thyroid isthmus; l, longus colli muscle; s, strap muscles; scm, sternocleidomastoid muscle; t, thyroid lobes; T, trachea (note the acoustic shadow); v, internal jugular vein; *, normal location of the parathyroid glands.
Anatomy
The thyroid gland consists of two ellipsoid lobes connected by an isthmus that extends across the lower cervical trachea (Figs. 9.1, 9.2). Normal thyroid parenchyma is homogeneous and hyperechoic relative to the muscles of the neck. Anatomic landmarks include the common carotid artery (CCA), internal jugular vein (IJV), trachea, and neck muscles. The sternocleidomastoid is seen as an oval muscle mass superficial and lateral to the thyroid. The strap muscles, the sternohyoid, sternothyroid, and omohyoid, appear as thinner muscle bands just superficial to the thyroid. The thyroid extends over the midline trachea between the CCA/IJV vascular bundles. It rests on the prevertebral longus colli muscles. The trachea, being air-filled, causes a bright reflection at its surface and a prominent acoustic shadow. The esophagus commonly extends from behind the tracheal shadow between the left thyroid lobe and the longus colli muscle. The esophagus has a target appearance that must not be mistaken for a thyroid or parathyroid nodule (Fig. 9.3). Identification of the esophagus is confirmed by observing the patient swallow, and observing air or fluid move through the esophagus.
The CCA courses along the lateral aspect of the thyroid lobe, which may partially envelop the CCA when the thyroid is enlarged. The IJV are seen lateral to the CCA.
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Enlarged lymph nodes may be detected along the vascular sheath of the CCA/IJV. The thyroid and parathyroid glands are supplied by the superior thyroid artery, a branch of the external carotid artery, and the inferior thyroid artery, a branch of the thyrocervical trunk from the subclavian artery. These arteries (1-2 mm diameter) and their accompanying veins (6-8 mm diameter) course between the thyroid lobes and the longus colli muscles. Spectral Doppler of the thyroidal arteries shows a high systolic velocity (20-40 cm/sec), low resistance (high diastolic velocity) pattern. The thyroid parenchyma shows a richly vascular pattern with power Doppler.
Figure 9.2 Normal Thyroid Echogenicity. Longitudinal image demonstrates the normal homogeneous mid-level echogenicity of the thyroid gland. Tiny cysts (arrow) are commonly seen in normal thyroid glands. These are large thyroid follicles and are commonly called colloid cysts. They are of no clinical significance.
Figure 9.3 Esophagus. The esophagus (arrow) commonly protrudes from behind the trachea (T) to the area between the thyroid gland and the longus colli muscle on the left, mimicking a thyroid or parathyroid mass. a, common carotid artery; t, left thyroid lobe.
Normal parathyroid glands are thin wafers 5 mm in diameter, but only 1 mm in thickness. Normal glands are not visualized by US. US reliably demonstrates adenomas and enlarged glands when they are in the neck. Most patients have four parathyroid glands, although 3% of patients have three glands and 13% have five or more. The paired superior and inferior glands are located deep to the lobes of the thyroid gland and superficial to the longus colli muscle. The inferior glands are ectopically located in the mediastinum in 3% of cases.
Thyroid
Thyroid Nodules
Most thyroid US is requested to evaluate suspected thyroid nodules. Nodules are exceedingly common, with nodules present in 50% of glands normal to palpation on autopsy series and in 18-36% of palpably normal glands on US studies [7,8,9]. Although thyroid cancer is the most common malignancy of the endocrine glands, it remains a rare disease accounting for less than 1% of all malignancy, and is the cause of death in only 0.005% of the United States population [10]. Most thyroid cancers are relatively non-aggressive and have a good prognosis with 90% 10-year survival for early disease. The challenge of US is to differentiate benign from malignant nodules. At this task, US fails because no sonographic finding is pathognomonic. To deal with this dilemma and to avoid a huge number of unproductive biopsies, criteria have been developed to select for biopsy only those patients who are at highest risk for carcinoma.
Malignant Thyroid Nodules
Thyroid carcinoma is 3 times more common in women with median age of 45-50 years at diagnosis. Radiation to the neck, especially in childhood, is a major risk factor, greatest at 20 years after the radiation [11].
Papillary carcinoma is most common (60-70%), is multifocal in 20-80% of cases, and spreads early to regional lymph nodes. The tumor is commonly at least partially cystic and
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the lymph node metastases are cystic in 25%. Punctate psammomatous calcifications are a strong sign of malignancy (see Fig. 9.5).
Figure 9.4 Dominant Nodule. Longitudinal image shows an ill-defined dominant nodule measuring 42 mm × 30 mm. The remainder of the thyroid gland was normal. This nodule was “cold” on radionuclide imaging. Biopsy is indicated.
Follicular carcinoma (15%) is invasive and spreads more commonly hematogenously to bones and lungs. It is uncommonly multifocal and less frequently spreads to cervical lymph nodes.
Medullary carcinoma (5-10%) may be familial (10% of cases) or associated with multiple endocrine neoplasia. Serum calcitonin is elevated and is a marker of disease.
Anaplastic carcinoma (5%) is exceptionally aggressive with average survival time of 6-12 months. The tumor is locally invasive and spreads rapidly to adjacent structures, nodes (which are commonly necrotic), lungs, and bone.
Metastases to the thyroid (from breast, lung, and renal cell carcinoma and melanoma) may be infiltrative masses or well-defined focal nodules.
Lymphoma accounts for approximately 4% of thyroid malignancy [12]. Older women are most commonly affected. The disease is usually non-Hodgkin’s lymphoma. Hypoechoic nodules grow rapidly and cause dysphagia or dyspnea. Enlarged lymph nodes are seen elsewhere. Cystic change in the enlarged nodes is common.
Benign Thyroid Nodules
Benign thyroid nodules are most commonly adenomatous nodules (adenomatous hyperplasia) or follicular adenomas. True thyroid cysts are exceedingly rare lesions. Most cystic
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nodules are cystic degeneration of hyperplastic nodules or adenomas. At least 15-25% of all thyroid nodules have cystic areas within them.
Figure 9.5 Psammomatous Calcifications. Transverse (A) and longitudinal (B) images show a solid thyroid nodule (between large arrows) with punctate calcifications (small arrows). These calcifications are highly predictive of malignancy. Biopsy was indicated and confirmed a papillary carcinoma.
Adenomatous nodules are nodules caused by hyperplasia of benign follicular cells. Most often the nodules are multiple. Cystic degeneration, hemorrhage, and calcification are common.
Follicular adenomas are benign neoplasms arising from follicular epithelium. Most are solitary with a well-developed fibrous capsule. Occasionally, adenomas are hyperfunctioning and result in hyperthyroidism with suppression of function of the remainder of the gland. These hyperfunctioning adenomas are “hot” on radionuclide scans.
Biopsy should be considered with the following findings that are associated with increased risk of malignancy:
  • Size >4-5 cm. Large dominant nodules are more likely to be malignant (Fig. 9.4). Few, however, reach size larger than 4 cm before coming to medical attention. Many physicians recommend biopsy of predominantly solid nodules larger than 15 mm.
  • Psammomatous calcifications. Microcalcifications <1 mm size (Fig. 9.5) scattered throughout a solid nodule are strong evidence of malignancy (70% positive predictive value) [13,14]. The calcifications appear as punctate echodensities. Many are too small to produce acoustic shadows. Psammomatous microcalcifications are strongly associated with papillary carcinoma. The microcalcifications may also be present in lymph node metastases.
  • Solitary cold nodule on radionuclide scan (Fig. 9.4). The risk of malignancy is approximately 15%.
  • History of neck irradiation, especially in childhood. The risk is highest at 20 years after radiation exposure and remains high for an additional 20 years [15].
  • Family history of thyroid malignancy, especially medullary carcinoma.
  • Age <20 years or male patient with solitary nodule. Benign thyroid nodules are uncommon in children and less common in males.
  • Irregular contour and poor margination (Fig. 9.4) suggest malignancy but may also be seen with benign nodules.
The following findings are most indicative of a benign lesion that can be followed conservatively or ignored:
  • Extensive cystic component is strongly indicative of benignancy (Fig. 9.6). Nearly all of these cystic lesions are the result of cystic degeneration in benign hyperplastic nodules or benign adenomas.
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  • Tiny cysts <5 mm size without an associated solid component are collections of colloid in macrofollicles (Fig. 9.7). These are benign and can be considered a normal finding.
  • Comet tail artifacts are produced by inspissated colloid [16]. Their presence is indicative of a benign lesion containing abundant colloid.
  • Homogeneous hyperechoic lesions are rarely malignant. Nearly all malignancies (and most benign nodules) are hypoechoic or isoechoic compared to thyroid parenchyma.
  • Peripheral rim-like, “eggshell” calcifications (Fig. 9.8) are indicative of a benign lesion.
  • Increased radionuclide activity, “hot” nodules with suppression of the remainder of the gland are nearly always benign.
Figure 9.6 Cystic Thyroid Nodule. Calipers (+, x) measure a predominantly cystic nodule in the right thyroid lobe, This is a benign thyroid nodule. Biopsy is not indicated. a, common carotid artery.
Figure 9.7 Colloid Cysts. Three tiny cysts (arrows) are seen in the left thyroid lobe. The largest of these measures 3 mm. These tiny cysts are normal findings. Biopsy is not indicated.
The following findings are indeterminate and are found with benign and malignant nodules:
  • Solid, hypoechoic or isoechoic, nodule (Fig. 9.9).
  • Amorphous dense calcification.
  • Complex nodule with irregular areas of cystic degeneration and hemorrhage (Fig. 9.10, 9.11).
  • Increased flow within a nodule on Doppler US (Fig. 9.11) [17,18].
  • Multiple nodules on US examination.
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Diffuse Thyroid Disease
Goiter
The word goiter refers to generalized enlargement of the thyroid gland. Goiter is not a specific diagnosis because thyroid enlargement has many causes, including iodine deficiency, Graves’ disease, adenomatous goiter, and thyroiditis. The size of the normal thyroid gland increases with body weight, decreases with age, and is larger in men than in women. Normal values are 19.6 ± 4.7 mL for men and 17.5 ± 4.2 mL for women [19]. Iodine deficiency goiter is not a significant problem in the United States because of iodine supplements in food.
Figure 9.8 Peripheral Rim-like Calcification. Longitudinal image reveals two nodules in the thyroid. One nodule appears solid but has a calcified peripheral rim (short arrow). The second nodule (long arrow) is predominantly cystic but has a solid component projecting from its wall (arrowhead). The appearance of each is consistent with a benign adenomatous nodule. Biopsy is not indicated.
Figure 9.9 Solid Nodule. US confirms a homogeneous solid thyroid nodule (between arrows) that corresponded to a palpable abnormality. Its benign or malignant nature cannot be determined by further imaging. US-guided biopsy revealed benign lymphocytic thyroiditis (Hashimoto’s thyroiditis).
Figure 9.10 Complex Nodule. This nodule is predominantly cystic but has a thick wall (arrow) and a prominent internal solid component. The appearance is indeterminate. A clinical decision must be made whether to biopsy or follow this nodule. This decision is based on integrating the size and appearance of a given nodule with the clinical information regarding the patient’s risk factors, laboratory evaluation, and medical history.
Figure 9.11 Complex Nodule with Increased Blood Flow. Gray-scale US (A) reveals a predominantly solid nodule with cystic components. The corresponding color Doppler image (shown here in gray scale) (B) reveals marked increased blood flow within most, but not all, of the solid tissue. Both the gray-scale and the color Doppler appearance are indeterminate. US-guided biopsy of the solid tissue confirmed a benign adenomatous nodule with degeneration.
  • Thyroid volume is calculated by measuring each thyroid lobe and adding together the size of lobes calculated by using the formula: Volume = length × width × height × π/6 (0.52) (Fig. 9.12).
  • Goiter is present when thyroid gland size exceeds 24.3 mL in men or 21.7 mL in women.
  • A thyroid isthmus >10 mm thick is indicative of thyroid enlargement (Fig. 9.13).
  • Iodine deficiency goiter shows diffuse parenchymal enlargement without abnormality of echogenicity.
Graves’ Disease
Graves’ disease (diffuse toxic goiter) is a chronic autoimmune disease that causes hyperthyroidism and goiter. Women are more commonly affected (7:1). Antibodies to thyroid stimulating hormone are present in the blood. Proptosis is commonly present.
  • The thyroid gland is diffusely enlarged, frequently 2-3 times normal size.
  • Thyroid echotexture may be homogeneous and normal, or diffusely hypoechoic.
  • Color Doppler shows a characteristic pattern of pronounced increased blood flow (“thyroid inferno”) manifest by multiple small dots of color signal throughout the gland during both systole and diastole [20].
Adenomatous Goiter
Multiple hyperplastic adenomatous nodules characterize adenomatous goiter (multinodular goiter).
Figure 9.12 Thyroid Measurement. The calipers (+) indicate the transverse dimension of the left thyroid lobe of a normal thyroid gland. A colloid cyst is present.
Figure 9.13 Thickened Thyroid Isthmus. A. The thyroid isthmus measured 13 mm (between calipers, +) confirming the sonologist’s subjective impression of goiter. The thyroid parenchyma is mildly heterogeneous. B. A normal thyroid gland and thyroid isthmus (2 mm thick) is shown for comparison.
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  • The thyroid gland is enlarged, asymmetric, and heterogeneous in echotexture (Fig. 9.14).
  • Multiple solid nodules of varying size and appearance are present. The nodules may be isoechoic, hypoechoic, hyperechoic, or mixed.
  • The nodules commonly have cystic areas of colloid concentration, foci of necrosis and hemorrhage, and coarse calcifications present.
Hashimoto’s Thyroiditis
This autoimmune process is the most common cause of hypothyroidism in the United States. Antithyroglobulin and antimicrosomal antibodies are present. The gland shows diffuse lymphocytic infiltration (chronic lymphocytic thyroiditis).
Figure 9.14 Adenomatous Goiter. Although this condition is commonly termed multinodular goiter, it frequently manifests as diffuse, heterogeneous thyroid enlargement without distinct nodules.
Figure 9.15 Hashimoto’s Thyroiditis. Longitudinal image shows a diffusely abnormal gland (between calipers, +, x) with a pattern of innumerable ill-defined hypoechoic nodules.
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  • A diffuse micronodular pattern of the thyroid parenchyma is characteristic (Fig. 9.15). The micronodules are hypoechoic and most are 2-3 mm in size (range = 1-6 mm) [21].
  • The gland is usually enlarged but may be normal in size.
  • Hyperemia is marked on color Doppler.
  • Radionuclide studies show little or no tracer uptake.
  • Distinct nodules are occasionally present (Fig. 9.9).
Subacute (de Quervain’s) Thyroiditis
Subacute (de Quervain’s) thyroiditis is a self-limited granulomatous inflammation of the thyroid probably caused by a viral infection. Also more common in women (5:1), the gland becomes painful and tender 2-3 weeks after an upper respiratory infection. Severe destruction of the gland releases hormone, resulting in a period of hyperthyroidism, followed by a short period of hypothyroidism caused by hormone depletion. Most patients recover fully.
  • The gland is initially enlarged but becomes atrophic as the disease progresses.
  • Diffuse decreased parenchymal echogenicity is seen in half [22].
  • The remainder show poorly defined hypoechoic nodules [22].
Atrophic Thyroiditis
Atrophic thyroiditis is an autoimmune disease that causes hypothyroidism in adults [23]. Circulating thyroid hormone levels are low, thyroid stimulating hormone levels are high, and autoantibodies to thyroid peroxidase and thyroglobulin are present in the patient’s serum. The disease is distinguished from Hashimoto’s thyroiditis by the small size of the gland.
  • Echogenicity of the thyroid gland is diffusely low.
  • The thyroid gland is atrophic. Combined volume of the thyroid lobes is <5.5 mL in males and <4.3 mL in females.
Acute Suppurative Thyroiditis
The thyroid is strikingly resistant to bacterial infection because of its copious blood supply, excellent lymphatic drainage, and high iodine content. Patients with suppurative thyroiditis present with fever and neck pain. US is used primarily to detect abscess. Congenital branchial pouch sinus tracts from the pyriform recess to the thyroid gland have been demonstrated in patients with recurrent suppurative thyroiditis [24].
  • The gland is diffusely enlarged and hypoechoic due to inflammation.
  • Focal fluid or air collections suggest abscess. Purulent fluid is commonly echogenic.
  • A sinus tract to the pyriform fossa is suggested by an irregular tubular lucency extending into the neck [25].
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Parathyroid
Hyperparathyroidism
Primary hyperparathyroidism is caused in 80-90% of cases by a solitary parathyroid adenoma, in 10-20% of cases by multiple hyperplastic glands, and in 1% of cases by parathyroid carcinoma [26]. The role of US is to preoperatively localize parathyroid disease in the neck. Ectopic parathyroid glands are best localized by Tc-99m sestamibi or MR [4,5]. Ectopic locations include the mediastinum (commonly in the thymus), behind the trachea, and high in the carotid sheath. US does not demonstrate mediastinal parathyroid adenomas.
Secondary hyperparathyroidism occurs in patients with chronic renal failure and chronic hypocalcemia. Parathyroid surgery or alcohol ablation is required when dialysis and medical therapy is ineffective in controlling calcium levels and the resulting bone demineralization and soft tissue calcification. Multiple hyperplastic parathyroid glands are present.
Parathyroid Adenoma
Solitary adenomas arise in each of the four parathyroid glands with equal frequency. “Incidental” parathyroid adenomas are occasionally discovered during sonography of the thyroid [27].
  • Parathyroid adenomas are of low echogenicity, substantially less than thyroid parenchyma (Fig. 9.16). The adenomas are usually found between the dorsal aspect of the thyroid lobe and the longus colli muscle. Thyroid tissue may partially or completely
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    envelop the parathyroid adenoma. Diffusely hyperechoic nodules or nodules with calcifications are much more likely to be thyroid, rather than parathyroid, nodules [28].
  • Most adenomas are 8-15 mm in size. Small lesions (<10 mm) are usually round, well defined, and nearly anechoic, but without accentuated through-transmission. Larger lesions tend to be oval, more heterogeneous, and lobulated in contour.
  • Giant parathyroid adenomas exceed 20 mm in size and are associated with greatly elevated levels of serum calcium and serum parathyroid hormone. These large tumors may develop cystic areas of necrosis and hemorrhage. Benign giant adenomas cannot be reliably differentiated from carcinomas.
  • Doppler demonstrates marked hypervascularity of the functioning adenomas. Prominent feeding vessels are evident [29].
  • Lymph nodes may mimic parathyroid adenomas. Lymph nodes are usually more intimately related to the carotid artery or are located inferior to the thyroid gland. Lymph nodes tend to have an echogenic center (see Fig. 9.18), whereas most parathyroid adenomas are uniformly hypoechoic.
  • Percutaneous fine needle aspiration with measurement of parathyroid hormone level is confirmatory of a parathyroid adenoma [30]. This procedure is particularly helpful when multiple thyroid nodules are present and identification of a parathyroid adenoma is uncertain.
Figure 9.16 Parathyroid Adenoma. Transverse (A) and longitudinal (B) images show the characteristic, homogeneous, hypoechoic appearance of a well-defined parathyroid adenoma (arrows). Note the characteristic location deep to the thyroid gland and superficial to the longus colli muscle (l). a, common carotid artery.
Multiple Parathyroid Gland Hyperplasia
Multiple gland disease may be caused by multiple parathyroid adenomas or hyperplasia of multiple glands.
  • Hyperplastic glands and adenomas have an identical sonographic appearance (Fig. 9.17).
  • The individual glands are commonly asymmetrical in size. Careful examination should always include looking for multiple enlarged glands.
Parathyroid Carcinoma
Parathyroid carcinomas are rare and may be difficult to distinguish from adenomas even histologically. Invasion of adjacent structures and prominent fibrosis provides evidence of malignancy. The cancer is aggressive and metastasizes early resulting in unrelenting hypocalcemia.
  • Carcinomas are larger, more lobulated, and more heterogeneous than adenomas.
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  • Most carcinomas are larger than 2 cm in size and may be indistinguishable from benign giant parathyroid adenomas.
  • Cystic components and heterogeneous internal echogenicity are signs of malignancy.
Figure 9.17 Multiple Parathyroid Hyperplasia. Longitudinal image through the left lobe of the thyroid demonstrates two enlarged hyperplastic parathyroid glands (arrows) in a patient with chronic renal failure and persistent elevation of serum calcium. Two more enlarged parathyroid glands were also seen on the right side.
Neck
Lymph Nodes
US is effective in demonstrating normal, enlarged benign, and malignant lymph nodes in the neck [31]. Differentiation of benign from malignant is often not possible but several US features are helpful in selecting nodes for biopsy.
  • Normal nodes are flattened, oblong, and small (<10 mm in smallest diameter) [32]. Normal nodes are hypoechoic with an echogenic hilus [33].
  • Benign, enlarged lymph nodes remain oblong in shape with a short-to-long axis ratio of 0.5 or less. Color or power Doppler reveals a normal vascular pattern of central vascularity radiating symmetrically from the hilum. The periphery of the node shows no vascularity [34]. Homogeneous echogenic fat extending from the hilum is a sign of benignancy (Fig. 9.18) [35]. Avascular nodes tend to be benign [34].
  • Nodes involved with lymphoma tend to mimic the Doppler characteristics of benign nodes [34]. Lymphoma nodes tend to be enlarged and homogeneous in echogenicity.
  • Malignant nodes are enlarged (>10 mm) with heterogeneous internal architecture and a round, rather than oblong, shape. Punctate calcifications and cystic changes are seen in metastatic nodes involved with papillary carcinoma of the thyroid. Color flow US shows deranged, irregular vascularity with decreased or absent hilar vessels and increased vascularity in the periphery [36].
  • Lymph node metastases may be cystic appearing as fixed masses with nodular irregular wall [37].
  • US can be used to guide fine needle aspiration biopsy of any questionable lymph nodes.
Thyroglossal Duct Cysts
These are the most common congenital cystic lesions in the neck. They arise from segments of the thyroglossal duct that fail to regress. Thyroid tissue is commonly present in the wall. Most present in childhood and are readily diagnosed by their characteristic midline position.
Figure 9.18 Benign Lymph Node. This enlarged cervical lymph node is markedly hypoechoic. Fat infiltrating the node from the hilum (arrow) is indicative of benignancy.
Figure 9.19 Branchial Cleft Cyst. Large mass (C) in the neck is filled with anechoic fluid and has a thin wall. Pathologic examination after surgical excision demonstrated respiratory epithelium lining the wall. S, shadowing from the spine.
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  • Cystic midline mass, usually at the level of the hyoid bone. They may be found in the midline from the tongue base to the suprasternal region.
  • Classic appearance is an anechoic, well-defined, unilocular cyst with increased through-transmission. Size varies from a few mm to 2-3 cm [38].
  • Many are hypoechoic with internal echoes, although nearly all show increased through-transmission [39].
  • Infection causes thickening of the walls and internal septations.
  • A soft tissue component within or around the cyst suggests the possibility of malignant degeneration (papillary carcinoma), a rare complication [40].
Branchial Cleft Cyst
These cysts are the congenital result of failure of obliteration of the embryonic branchial cleft in the eighth to ninth fetal week. Most (95%) arise from a remnant of the second branchial cleft [41]. They most often present in young adults.
  • Cystic, thin-walled, round to oval mass, near the angle of the mandible (Fig. 9.19). Size ranges from 2-3 mm to 7 cm.
  • The mass displaces the sternocleidomastoid muscle posteriorly, the CCA and IJV medially, and the submandibular salivary gland anteriorly.
  • Infection is relatively common.
Cystic Hygroma
Most cystic hygromas (90%) enlarge rapidly after birth and are discovered before age 2. They result from congenital blockage of regional lymphatic drainage. Cystic hygroma is the common name for the cystic form of lymphangioma.
  • Classic appearance is a thin-walled, multiseptated cyst in the posterior triangle of the neck. Septa are of variable thickness [42].
  • Extension into the mediastinum is found in 3-10% of cases [37]. Lesions dissect through tissue planes as they expand.
  • Lymph is anechoic. The presence of internal echoes suggests that hemorrhage has occurred.
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Teratomas
Most teratomas in the neck originate within or near the thyroid gland [37]. Nearly all are benign, but they may cause respiratory obstruction.
  • Dermoid cysts have internal echoes (from keratinous debris) with slight or no accentuated through-transmission [43]. The cysts are sharply defined with smooth borders. Absence of internal vascularity on Doppler US helps to confirm the cystic nature of the lesions.
  • Solid teratomas are rare and are heterogeneous in appearance.
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