ULTRASOUND OF THE NECK

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High-resolution B-mode sonography has improved in the past few years and has become a very valuable tool in the diagnosis of diseases of the head and neck. Sonography is commonly the first imaging modality after clinical examination. It is easily tolerated by patients and is inexpensive. It provides valuable diagnostic information with a high degree of diagnostic accuracy. On the basis of the sonographic findings, selection of additional imaging modalities including CT and MR imaging can be applied more judiciously. This article provides the most up-to-date information about the indications, findings, and limitations of high-resolution B-mode sonography in the evaluation of head and neck pathology.

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INSTRUMENTATION

Optimal ultrasound (US) examination of the superficial structures of the head and neck requires appropriate equipment with high-resolution small-parts transducers that make use of high-frequency US. US sequences between 5 and 20 MHz are used (most commonly 7.5 to 10 MHz). Either the transducer is placed directly on the skin or a silicon stand-off pad is placed between the transducer and the skin to get ideal contact with the surface, especially in the angle of the jaw and the neck.

EXAMINATION TECHNIQUE

A systematic examination protocol is mandatory for the evaluation of the head and neck. It begins with the examination of the thyroid gland where the instrument is adjusted and frequency and gain are optimized. The examination is continued along the vascular sheath to the floor of the mouth, tongue, and the salivary glands and tonsils. The next step is to examine the status of the lymph nodes including nuchal, accessory, and transverse cervical nodes. If clinically indicated, the larynx and

CERVICAL LYMPH NODES

The majority of the normal lymph nodes in the head and neck show an axial diameter of 2 to 5 mm with the exception of the jugulodigastric and the jugulo-omohyoid lymph nodes, which are larger and reveal an axial diameter of 8 to 10 mm, and a longitudinal diameter of 15 to 20 mm.10, 15, 35 Normal lymph nodes are difficult to detect because of their high echogenicity, which is similar to that of the surrounding fatty tissue. They can only be demonstrated by the use of high frequencies (13 MHz).11

REACTIVE LYMPH NODES

Enlarged reactive lymph nodes are the most frequent sonographically encountered entities in the head and neck in nonselected patients. Some reactive lymph nodes are found in nearly every patient, most commonly the submandibular and lateral cervical nodes. The reactive enlargement of the lymph nodes is the response to past inflammatory disease and is reflected by histiocytosis in the lymph node sinus.

The typical sonographic appearance shows a longitudinal-to-oval shape with rounded poles and a

INFLAMMATORY LYMPH NODE DISEASE

In acute, nonspecific lymphadenitis the lymph nodes are painful and markedly enlarged. Their shape is longitudinal or ovoid with rounded poles. In addition, they may be round to spherical with smooth borders and display a hypoechoic appearance. The hilus of the lymph node is not always apparent. The differentiation from the surrounding soft tissues and from other lymph nodes, however, is mostly discernible (Fig. 2). The enlargement of acute inflammatory lymph nodes ranges from 20 to 25 mm in

SPECIFIC LYMPHADENITIS

Specific lymphadenitis is principally caused by tuberculosis. The involved lymph nodes are commonly large, painless, or slightly painful under pressure. There is a significant discrepancy between the individual involved lymph nodes, with a spectrum ranging from large, round, nonechoic, to cystic-necrotic nodes with blurred borders. The surrounding uninvolved lymph nodes appear reactive and hyperplastic.7, 66 Edema in the surrounding tissue adjoining the tuberculous lymph node mass imparts a

PRIMARY LYMPH NODE DISEASES

Sarcoidosis (Boeck's disease) is a benign granulomatous disease of the lymph nodes, whereas Hodgkin's and non-Hodgkin's lymphomas are aggressive malignant lymph node neoplasms. Both reveal sonographically similar and overlapping features. In nearly every case multiple lymph nodes are involved (e.g., one or two regional groups), which result in conglomeration of the enlarged lymph nodes. The individual nodes are round to oval in shape. A solitary involvement of only one lymph node is rare. On

LYMPH NODE METASTASES

Cervical lymph node metastases in the head and neck region are caused by squamous cell carcinoma in 80% of cases. Characteristic sonographic findings of metastatic lymph node disease are enlargement with a round-to-spherical shape. Commonly they are hypoechogenic, occasionally inhomogeneously echogenic, with a loss of the hilar definition. In cases of extranodal spread with infiltrative growth, the borders are poorly defined.2, 13, 16, 19, 29, 47, 48, 53, 58, 61, 67 Common findings of

Hemangiomas and Lymphangiomas

These lesions occur most commonly during the first 2 years of life or even in utero. They are divided into capillary or cavernous and are multicystic, fluid-filled cavities. The echogenicity is variable and depends on the size of the cystic component. They can be hypoechoic or more or less isoechoic, but usually are hyperechoic compared with the surrounding cervical soft tissues. They are highly compressible.15

Cystic lymphangioma (hygroma) can be firm and elastic, so that palpation often

TUMORS OF THE CAROTID BODY (CHEMODECTOMAS)

Carotid body tumors are typically localized within the carotid bifurcation or adjacent to the carotid arteries with displacement of the internal and external carotid arteries. These tumors are highly vascular, which can usually be demonstrated by B-mode sonography (Fig. 11). CCDS displays the mass and its vascularization. The diagnosis of a carotid body tumor is based on the sonographic findings of a mass at the carotid bifurcation with increased vascularity.17, 32

ABNORMALITIES OF THE CERVICAL VESSELS

Aneurysms, elongation, and tortuosity of the carotid arteries can cause tumorlike swellings in the neck that can be mistaken for a tumor or a lymph node lesion.40, 62 They usually manifest as a pulsatile neck mass. A partially thrombosed aneurysm of the carotid artery is rare but may simulate a tumor. B-mode sonography is capable of delineating an aneurysm or tortuous carotid arteries (Fig. 12). The additional use of CCDS clarifies the diagnosis and differentiates thrombotic, nonperfused

CYSTIC LESIONS

Cystic lesions in the head and neck are not uncommon. The frequency of cysts in the head and neck is in the range of 1% to 10%.69 According to publications in the literature there are more than 20 different cystic entities.21, 27, 69 The most common cysts originate from the thyroid gland, the thyroglossal duct, and branchial clefts, followed by cystic lymphangiomas. The remaining cystic lesions include ranula, dysodontogenetic cysts, laryngoceles, and so forth. In patients with metastatic

SALIVARY GLANDS

The parotid, the submandibular, and the sublingual glands can be visualized sonographically. The glands are typically homogeneous echogenic structures. The intraglandular and extraglandular ducts can only be visualized sonographically by use of high-frequency, high-resolution transducers (11 MHz and higher). The facial nerve in the parotid gland most often cannot be visualized. Inflammatory disease is the most common abnormality of the salivary glands. The ratio of the different diseases of the

TUMORS OF THE SALIVARY GLANDS

Salivary gland tumors constitute about 0.3% of all neoplasms. They are located in the parotid glands in 70% to 80% of cases. Pleomorphic adenomas comprise 70% to 80% of parotid tumors, whereas 5% to 10% are papillary cystadenoma lymphomatosum (Wharthin's tumor). Tumors of the parotid glands are malignant in about 10% of cases, of the submandibular gland, in about 45%, and of the sublingual glands in about 90% of cases.46, 65

INTRAGLANDULAR METASTASES

Lymph node metastases of the parotid gland can occur, most commonly from malignant melanoma and squamous cell carcinoma of the skin and metastatic carcinoma of the breast and lung. Malignant lymphomas can involve the intraglandular parotid lymph nodes.

SWELLING OF SOFT TISSUES (PSEUDOTUMORS)

There is nonglandular circumscribed or diffuse swelling of the soft tissues in the neck including edema, lipomatosis, hematoma, and low-grade infection, which may mimic a tumor. They can be differentiated from a neoplasm or enlarged lymph nodes by sonography in conjunction with palpation.

HYPERTROPHY OF MASSETER MUSCLES

Hypertrophy of the masseter muscle can occur on one or both sides. Clinically, it may be misinterpreted as a tumor of the salivary glands.55 The differentiation is easily made by US. A functional assessment is performed with measurement of the masseter muscle in a relaxed position and a strained position while biting.

INFECTION OF THE NECK, TONSILS, TONGUE, AND FLOOR OF THE MOUTH

Inflammations in the area of the neck, tongue, and floor of mouth are not uncommon and can be caused by dental infection, tonsillitis, pharyngitis, and occasionally by foreign body perforation. US is useful for the evaluation of the extent and location of the inflammatory process and the search for an abscess cavity that necessitates surgical intervention. In phlegmon there is diffuse inflammatory edema in the neck and fascial spaces surrounding muscles and the great vessels. Sonographically an

TUMORS OF THE TONGUE AND FLOOR OF THE MOUTH

Benign tumors in the oral cavity are mostly papillomas of the tongue; goiter of the base of the tongue, and some mesenchymal tumors including fibroma, lipoma, or neurinoma. The most common benign tumor of the tongue in babies is hemangioma, which is most commonly congenital and causes macroglossia with a tendency to bleed. These hemangiomas can be diagnosed sonographically. They usually shrink in the course of years, which can be documented by US. This eliminates the need for MR imaging

SUMMARY

Sonography, when performed by an experienced examiner, can be used for evaluation of many pathologies in the head and neck area. Some benign neck lesions, such as cysts, lipomas, carotid body tumors, and hyperplastic lymph nodes, have typical sonomorphology. Sonography has an accuracy rate of about 90% in cervical lymph node staging and can delineate subclinical lymph node recurrences. It is the method of choice for evaluation of tumor infiltrations of the wall of the great vessels. Salivary

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