Head and Neck Ultrasonography
- Author: Yuemi An-Grogan, MD; Chief Editor: Gowthaman Gunabushanam, MD, FRCR more...
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.
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 7.5-10 MHz but ranging anywhere from 5-20 MHz. The higher the frequency, the better the spatial resolution.
B-mode ultrasonography allows 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.
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 reviewed below.
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 its surroundings.
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, whereas deeper structures will appear more “bright.”
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 :
Miscellaneous mass lesions
Infection and trauma
According to one study, an increase in thyroid cancer may be attributable to the increased use of thyroid ultrasound and fine-needle aspiration (FNA). Between 2000 and 2012, although the incidence of thyroid cancer doubled, there was a nearly 5-fold increase in the use of thyroid ultrasonography and a 7-fold increase in thyroid FNA.
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.
This article does not discuss orbital or sinus sonography or procedural ultrasonography involving the head and neck. This article is a brief overview of common practices and pathology of the head and neck using ultrasonography.
Specific indications are as follows:
Evaluation of head and neck anatomy
Evaluation of masses
Evaluation of nodal disease in the head or neck region
Assessment of infections or abscesses in the head or neck region
Evaluation of cysts or glandular pathology in the head or neck
Neoplasms arising from head or neck
Procedural guidance for central line placement, tissue biopsy, fine needle aspiration, among others (not discussed in this article).
No absolute contraindications for head and neck ultrasonography are recognized; however, it should not be performed if it delays definitive care in an emergent situation.
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 high-frequency linear array probe for head and neck applications because structures of interest are superficial.
Complications arise when using ultrasonography to guide procedures into the neck.Avoid mistaking cyst for a vessel by rotating probe 90° to visualize the vessel in long axis. Use color/spectral Doppler ultrasonography to assess flow and waveform.
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