Diagnosis of Head and Neck Lesions With Ultrasonography Technique

Ultrasonography is the study of choice in infants with open fontanelles and sutures and can be used to evaluate premature fetuses for various intracranial pathologies or malformations, such as hydrocephalus or hemorrhage. Particularly, brain ultrasonography is a well-established method that is useful for both the initial evaluation and the follow-up of intraventricular hemorrhage, parenchymal hemorrhage infarct, and periventricular leukomalacia.

The differential diagnoses for the different types of hemorrhagic brain diseases may be limited with ultrasonography; thus, MRI may be preferable. ^[11]

Neonatal head ultrasonography reveals the following:

• Germinal matrix hemorrhage

• Ventricular measurements

• Normal variants (eg, choroid plexus cysts, benign macrocrania)

Using the high-frequency linear transducer and placing the probe over each of the open fontanelles allows visualization of the coronal and transverse views of the brain. Depth and gain adjustments commonly need to be made in order to visualize the entire structure of interest.

Hemangioma

Hemangiomas are the most common congenital lesions found in neonates, and the most affected sites are the head and neck. They can present as palpable subcutaneous masses, cutaneous skin lesions, or a combination of both. They tend to grow rapidly for months and then spontaneously resolve over the next several years.

Although these lesions are infrequently imaged, ultrasonography is the initial study of choice for these lesions because it is noninvasive, safe, and easy to perform on infants. Hemangiomas are microscopically vascular lesions and rarely show up as vascular lesions on US imaging. However, when these lesions are visible, color duplex ultrasonography shows heavy vascularization within the lesion. The depth of the lesion varies but can also be measured with ultrasonography using the calibrations on the side of the screen.

Using the high-frequency linear transducer, the probe is placed over the structure of interest, fanning through the lesion using B mode and color duplex for enhanced visualization.

Thyroid diseases are one of the most common indications for head and neck ultrasonography. Ultrasonography can identify structures as small as 2 mm in diameter. Ultrasonography assists with tissue characterization, helps determine the etiology, assists in evaluating whether a mass is benign or malignant, and can aid in the treatment of either medical or surgical thyroid-related diseases. ^{[12, 13, 14, 15, 16, 17, 18]}

Ultrasonography applications for thyroid investigation include the following:

• Normal thyroid anatomy

• Lymphadenopathy

• Goiter

• Thyroiditis

• Autoimmune disease

• Fine-needle aspiration for histologic determination ^[19]

• Routine screening for thyroid cancer ^[20]

The thyroid gland is a highly vascular gland that is composed of 2 bilateral elongated lobes with superior and inferior poles connected by an isthmus. Usually, 2 pairs of parathyroid glands lie in proximity to the thyroid gland. On ultrasonography, thyroid tissue has a homogeneous, medium-gray echotexture. ^[21]

Hemorrhage within the thyroid tissue is hypoechoic. Debris appears as heterogeneous echoes within the tissue. Cystic structures appear anechoic and have a thin wall with posterior acoustic enhancement. Calcifications are hyperechoic and create "shadowing," obstructing the tissue plane behind it.

Ultrasonography is the imaging study of choice for thyroid nodules, providing the following:

• The ability to examine nodules that are too small to be palpated

• Identification of multiple nodules

• Precise nodule measurements and ultrasonographic characteristics for monitoring and disease classification

Solid appearance, increased vascularity, microcalcifications, irregular margins, and the absence of a halo are features associated with malignancy. ^[22]

The ultrasonographic appearance of the affected gland reflects the histopathologic changes that occur: diffuse infiltration of the thyroid parenchyma with lymphocytes and fibrosis. Thus, on ultrasonography, the thyroid parenchyma appears heterogeneous, dotted with small hypoechoic nodules, usually measuring a few millimeters in diameter and separated by echogenic septae. ^[21]

Using a low-frequency transducer, the dimensions of each lobe should be determined in the sagittal and transverse planes to determine length, anterior posterior depth, and transverse width of gland. Then this formula for volume can be applied: V = 0.5 x (L x D x W).

The total volume of the thyroid gland is obtained by summing the volumes of the 2 lobes. This measurement is an estimate and may become increasingly inaccurate the larger the gland. ^[23]

When a thyroid nodule has been detected, an ultrasound examination, with or without fine-needle aspiration, should be the first test performed. Ultrasonography can reliably identify solid nodules of more than 3 mm and cystic nodules of more than 2 mm.

Ultrasound characteristics of benign thyroid nodules include the following:

• Clear, demarcated edges of the nodule

• Cystic structure - Thin walled, fluid filled, anechoic (no echoes inside, without tissue or vessels)

• If many cysts throughout thyroid – Benign multinodular goiter

Ultrasound characteristics of malignant nodules have the opposite characteristics. Usually, they are solid, hypoechoic, and taller than wide and may or may not be hypervascular on color Doppler imaging.

Thyroid ultrasound with gray-scale and color Doppler imaging has been shown to be successful at differentiating normal thyroid parenchyma from diffuse or nodular thyroid disease by evaluating gland size, echogenicity, echotexture, margins, and vascularity. ^[12]

Ultrasound-based classification systems exist for stratification of thyroid nodules based on risk of malignancy, such as the Thyroid Imaging Reporting and Data System (TIRADS). According to a systematic review by Mistry et al, for TIRADS, the mean values for sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 90.0%, 57.4%, 49.0%, and 91.0%, respectively. ^{[13, 15]}

 

Goiter

The incidence of goiter using ultrasonography is about 5%. Iodine deficiency contributes to the incidence far more in developing countries. Other causes include autoimmune thyroid disorders and inflammatory diseases of the thyroid gland. The development of goiter is one of progressive thyroid enlargement, which may result in worsening dyspnea and dysphagia. Substernal goiters may cause progressive compression of major vascular and airway structures. ^[24] Hormone therapies are first-line treatments to reduce the size of the goiter. However, in many cases, surgical intervention is needed.

Ultrasound elastography

Ultrasound elastography is an imaging technique that has been used in the diagnostic workup of nodular thyroid disease to further investigate the tissue for malignancy. Strain elastography indicates the stiffness in tissues, which is defined as the change in length during compression divided by the length before compression (E = stress/strain). The World Federation for Ultrasound in Medicine and Biology (WFUMB) has produced guidelines for the use of elastography techniques. According to the WFUMB, for shear wave elastography (SWE), some systems require a lower-frequency transducer (9 MHz), and in such cases, the high-frequency transducer should be used for the B-mode, and the lower-frequency probe should be used for SWE. ^{[25, 26, 16, 17, 18]}

Ultrasonography is the imaging modality of choice for differentiating whether a neck mass is cystic or solid and whether it is thyroidal or extra-thyroidal. It is also routinely used for guiding fine-needle aspiration and abscess drainage. Using the high-frequency linear transducer, place the probe along the affected area for visualization, avoiding the cervical spine because visualization is poor distal to bone.

Malignant lymphoma

Lymphomas include histologically different diseases of the lymphatic tissues, such as Hodgkin lymphoma and non-Hodgkin lymphoma. Patients often present with general conditions of malaise, fever, weight loss, and anemia and either single or multiple lymph node swelling. Lymph node swelling is often found in the cervical or inguinal region. Ultrasonography findings show enlargement and hyperemia of the lymph nodes, generally along the cervical chain in the neck. ^{[1, 27]}

Thyroglossal duct cyst

These are the most common congenital anomalies of thyroid development found on ultrasonography and are usually diagnosed by 20 years of age. They are usually located in the midline anywhere from the base of the tongue to the thyroid isthmus and develop when the duct fails to completely atrophy after the thyroid descends into position and can have the potential to become malignant. ^{[28, 29]}

Ultrasonography findings include a hypoechoic or anechoic, well-circumscribed cystic structure in the anterior floor of the mouth.

Occasionally the lesions can be multicystic; in 1% of cases, papillary adenocarcinoma can develop. In these cases, ultrasonography reveals an increase in size of the cysts, and solid tumor tissue fills the cystic lesion. ^[1]

(See the images below.)

Branchial cleft cyst

Branchial cleft cyst (BCC) anomalies may develop in any of the 4 branchial clefts. They are usually in the lateral cervical region, ventrolateral to the carotid bifurcation. Type II BCC constitutes 95% of all BCCs.

Ultrasonography findings include a fluid-filled, anechoic, compressible structure lateral to the carotid artery. Ultrasonography can often show a fine granular echo pattern caused by cellular debris or crystals of cholesterol within the fluid. ^[1]

Lymph node disease/metastasis

Up to 80% of malignant lymph node metastases originate from squamous cell carcinoma (SCC), often originating in the oropharyngeal cavity. Patients usually present with painful cervical swelling.

Ultrasonography findings include the following:

• The center of the lymph node is echo free (more hypoechoic than normal), consistent with necrosis.

• Compression or invasion into the internal jugular vein may be visible.

• Metastases from SCC are often not highly vascular, varying from thyroid lesions, although vascularity of a node is difficult to assess. ^[1]

Sensitivity of ultrasonography in the diagnosis of cervical lymph node metastases is approximately 89-95%, whereas specificity is about 80-95%. The lower specificity is due to the difficulties in differentiating between enlarged nodes of lymphoid hyperplasia and enlarged metastatic nodes. The most important criterion in the ultrasonographic diagnosis of metastatic nodal disease is having the round to spherical shape when compared to nonmetastatic nodal disease. ^{[30, 31, 32, 33]}

Parathyroid

Generally, a normal parathyroid gland is not well visualized on ultrasonography because of its deep location and small size. However, parathyroid adenomas larger than 1 cm should be visible. Ultrasonography findings of parathyroid adenomas include the following:

• Usually circular to ovoid solid lesions with well-defined margins

• Homogeneously hypoechoic (unlike lymph nodes)

• Usually highly vascular, reflected on color duplex sonography

Parathyroid carcinomas are difficult to differentiate from adenomas by ultrasonography alone; thus, biopsies are helpful in this situation. ^[34]

Characteristics of malignancy include the following:

• Cystic degeneration

• Local tissue invasion

• Calcifications or increased internal heterogeneity

Parathyroid cysts are ultrasonographically similar in appearance to other cysts of the head and neck. ^[35]

For lesions in the parotid, submandibular, and sublingual glands, ultrasonography is an ideal tool for initial assessment, since these structures are relatively superficial. By using high-resolution techniques, one can obtain excellent resolution and tissue characterization without unnecessary radiation hazard. For the deeper and more minor glands or for further investigation, CT or MRI is the modality of choice. ^{[36, 37]} Below is a brief overview of common processes involving the salivary glands. Of special consideration, the role of ultrasonography in evaluating facial structures, such as salivary glands, is neither sensitive nor specific and is most valuable in acutely ill patients to assess for infectious processes such as abscess or obstruction.

When using ultrasound-guided FNA to diagnose lesions of the salivary gland, the adequacy of the sample depends on the lesion's composition or vascularity. ^[38]

The normal parotid gland has a homogeneous echo texture, comparable to that of the thyroid gland, and can (as a normal variant) demonstrate numerous intraparenchymal lymph nodes. ^[39]

Acute parotitis can result from either viral or bacterial infections. If bacterial, which is less frequent, it is usually unilateral. Whereas viral parotitis on ultrasonography is relatively hypoechoic with a heterogeneous texture, bacterial parotitis demonstrates areas of suppuration in the gland as anechoic or hypoechoic foci, possibly with enlarged intraparotid lymph nodes. ^[39]

Malignant neoplasms of the parotid gland

The most common malignancies of the salivary gland include mucoepidermoid carcinoma, acinus cell carcinoma, adenocarcinoma, and adenocystic carcinoma (in descending order). ^{[40, 41]}

Patients often present with swelling and pain, compared with benign lesions. If found in the parotid gland, when compared with benign lesions, the incidence of facial nerve involvement is increased.

Ultrasonographic findings of malignant tumors show irregular borders and heterogeneity of structures. Shadowing may be observed behind the lesions, and infiltration or invasion into adjacent soft-tissue structures and surrounding muscles is often observed. ^[1]

High-resolution ultrasonography is the first-line examination for parotid gland diffuse disease and focal lesions, normally using gray-scale and color Doppler ultrasonography. ^[41]

Pleomorphic adenoma

Pleomorphic adenomas are the most common benign salivary gland tumors. Incidence is highest in the parotid gland. They present clinically as firm mobile swellings of the gland; they are often painless and spare the facial nerve. They are composed histologically of mixed tissues.

Ultrasonographic findings are varied as well. Usually well circumscribed, homogeneous patterns with decreased echogenicity are evident. Adenomas are usually noncompressible structures with a regular border. Occasionally, the tumor is hyperechoic, and cystic areas or calcifications may be seen within the mixed tissue.

Warthin tumor

Warthin tumor is the second most common salivary gland tumor and is usually found in bilateral parotid glands, with a strong male predominance. Ultrasonography usually reveals multiple cystic changes in respective glands.

Sialoliths of the salivary gland

Sialoliths are the most common cause of salivary obstruction. ^{[42, 38]} They are usually found in the submandibular gland. Patients usually present with pain, redness, and swelling. The glands may demonstrate inflammatory changes throughout the years and have the potential to get infected and form abscesses.

Ultrasonographic findings include the following:

• Hyperechoic sialolith with a posterior shadow

• Duct dilation

Sialadenitis

Sialadenitis, like sialoliths, usually affects the submandibular gland, rather than the parotid gland. As in acute parotitis, patients often present with pain, redness, and marked swelling. This condition can be caused by radiation or viral and bacterial infections.

Ultrasonographic findings include the following:

• Massive enlargement of the gland

• Irregular echogenic structures

• Hyperemia

• Possible sclerotic changes