Background
Practice essentials
Ultrasonography is one of the few diagnostic modalities that can be done at the bedside and offers many advantages over other modalities. It is readily accessible and portable, and images are viewed in real time. In addition, it is less expensive and noninvasive than other modalities. Sedation and contrast dye are rarely needed; however, newer studies with contrast are emerging. Most importantly, it is a safe study and, thus, is the first recommended imaging of choice for pregnant women and children. [1]
Ultrasonography does have some limitations. The accuracy and effectiveness relies on the experience and skill of the operator for image acquisition and the physician for image interpretation. Furthermore, it is a study whose resulting outcome varies, depending on the patient’s body habitus and cooperation. Lastly, ultrasonography requires a window that is unimpeded by bone or air, limiting the type of evaluations it offers, when compared with CT scanning or MRI.
For the head or neck evaluation, a high-resolution, small-part transducer with higher frequencies is used, most commonly between 7.5 and 10 MHz, but ranging from 5-20 MHz. The higher the frequency, the better the spatial resolution. According to American Institute of Ultrasound in Medicine (AIUM) recommendations, mean frequencies of 10-14 MHz or greater are preferred. [2]
Point-of-care ultrasound (POCUS) of the head and neck plays an important role in the diagnosis and treatment of upper airway stenosis, swelling, and painful diseases of the neck, as well as evaluation for swallowing problems. A linear probe with a frequency of around 10 MHz and a field of view of around 40 mm is suitable for head and neck POCUS. Upper airway POCUS should also be performed for dyspnea. [3]
Ultrasound-guided nerve blocks are commonly performed by pain physicians because of advantages over fluoroscopy in that ultrasonography is portable, is radiation-free, and offers real-time imaging. [4]
Ultrasound-guided fine-needle aspiration cytology (FNAC) for head and neck malignancy has been found to be highly reliable and specific. In a study by Petrone et al, only 8 samples of 301 lesions (2.6%) were considered nondiagnostic. Cytologic-histologic correspondence was 89%. Overall sensitivity was 92.75, and specificity was 94.6%. [5]
Ultrasound-guided core needle biopsy (USCNB) for head and neck lymphoma has been shown to be a successful diagnostic technique. In one study, by Cuenca-Himenez, USCNB was diagnostic of lymphoma in 215 of 226 (95.1%) patients. Eleven patients required a subsequent surgical excision biopsy for diagnosis. [6]
Thyroid-stimulating hormone, free T4, and parathyroid hormone testing are useful screening tests for patients with clinical concern for thyroid disease or hyperparathyroidism, respectively.
B-mode ultrasonography shows the texture and tissue borders as black and white pictures. Color duplex ultrasonography allows for visualization of moving tissues and blood flow. Doppler ultrasonography allows differentiation of the vessels. With the different modalities combined, it allows the reader to evaluate for hyperemia, vessels relative to pathologic findings, inflammatory changes, and the components of the structure being investigated.
Transcranial Doppler ultrasonography is used to assess intracranial blood flow velocity, emboli, stenosis, and vasospasm secondary to subarachnoid hemorrhage. It is also used to diagnose right-to-left cardiac shunting, most commonly a patent foramen ovale, in patients after a stroke.
Definitions and guidelines
Basic understanding is needed of the structures of the head and neck as well as knowledge of how sound waves create real-time images. Key principles and definitions of ultrasound are described:
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Echogenicity is the ability of a surface to bounce an echo or return a signal. Hyperechoic structures are more “bright” than their surroundings, whereas hypoechoic structures are less “bright” than their surroundings. Anechoic structures appear black, without echoes; whereas isoechoic structures have the same echoes as their surroundings, which means it appears as bright as its surroundings.
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Acoustic impedance is transmission and reflection across 2 different boundaries/surfaces. Acoustic shadowing shows areas through which sound waves fail to propagate. Acoustic enhancement is when no echoes are reflected and sound is allowed to pass through, allowing echoes deep to the anechoic structures to be visible. Fluid-filled structures provide acoustic enhancement, making the structures/area inferior to it brighter.
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Refraction is produced from the multiple reflections from an object if the acoustical impedances of tissue layers are too different. Attenuation is the reduction of the ultrasound beam as it passes through a medium.
The American Institute of Ultrasound in Medicine (AIUM), in conjunction with the American Academy of Otolaryngology–Head and Neck Surgery, has published guidelines on the use of head and neck ultrasound examination for the following [7] :
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Salivary glands
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Lymph nodes
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Congenital lesions
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Miscellaneous mass lesions
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Infection and trauma
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Endocrine glands
The European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) has described training requirements for head and neck ultrasound on the basis of 3 EFSUMB competency levels, as follows [8] :
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Level 1 involves the knowledge and skills needed to perform essential head and neck ultrasound examinations independently.
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Level 2 describes the skills needed to perform ultrasound-guided interventions. Practitioners who need to perform ultrasound-guided interventions in clinical work would be expected to hold Level I and Level 2 competencies and skills.
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Level 3 involves training and practice on a more advanced level and requires additional knowledge of advanced ultrasound technologies and engagement in education or research.
Indications
Initial screening and diagnostic studies using ultrasonography have become more favored, especially with increasing evidence supporting future potential harm with the use of ionizing radiation. Ultrasonography is highly useful for many disease processes and many organ systems. Specifically, it is an effective clinical tool to evaluate head and neck anatomy and pathology. It can play an important role in the workup, staging, treatment planning, and posttreatment follow-up of patients with diseases involving the head and neck.
Specific indications include the following:
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Evaluation of head and neck anatomy
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Evaluation of masses
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Evaluation of nodal disease in the head or neck region
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Assessment of infections or abscesses in the head or neck region
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Evaluation of cysts or glandular pathology in the head or neck [9]
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Neoplasms arising from the head or neck
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Procedural guidance for central line placement, tissue biopsy, fine-needle aspiration
Technical Considerations
Ultrasonography is especially useful when a patient has had recent exposure to radiation or when evaluating a pediatric patient for whom you want to spare radiation. In addition, ultrasonography is highly useful in the pregnant population.
Use a high-frequency linear array probe for head and neck applications because structures of interest are superficial.
All written reports should be in accordance with American Institute of Ultrasound in Medicine (AIUM) practice parameters for ultrasound examination documentation. In the event that a delay would have an adverse effect on the patient's outcome, direct verbal or electronic communication between the interpreting provider and the patient's health care provider is required. [10]
Complications arise when using ultrasonography to guide procedures into the neck. Avoid mistaking a cyst for a vessel by rotating the probe 90° to visualize the vessel in long axis. Use color/spectral Doppler ultrasonography to assess flow and waveform.
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Biopsy-proven carcinoma of the right thyroid gland, nodule shown between the arrows.
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Thyroiditis on Doppler imaging of the right thyroid gland showing hypervascularity. (Image A)
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Normal thyroid vascularity on color Doppler imaging. (Image B)
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Axial section of the right lower thyroid gland showing a hypoechoic nodule inferior to the thyroid gland consistent with parathyroid adenoma (between the arrows).
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Sagittal and axial section of the left parotid gland showing anechoic rounded lesion suggestive of simple benign cyst.
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Sagittal image of the right parotid gland showing homogeneous normal parenchyma.
