The head and neck can be a challenging area for ultrasonography due to the proximity of structures, including the trachea, musculature, carotid artery, jugular veins, and multiple nerves. However, using an organized strategy for scanning and an increased familiarity with the anatomy, there can be numerous diagnostic and interventional opportunities in this area of the body. Starting at the midline, the cricothyroid membrane can be located via manual palpation. Placement of a high-frequency linear ultrasound probe at midline in the transverse plane allows for evaluation of the trachea at this level. Typically, the cricothyroid membrane can be seen as a thin hyperechoic sliver just superficial to a significantly more hyperechoic layer that is the air–mucosal interface within the trachea[1] [Figure 1]. There are likely several artifact layers that appear as additional hyperechoic lines deep to the air–mucosal interface. This view allows for visualization of the trachea and can help assess for correct positioning of an endotracheal tube or help with the administration of a translaryngeal block for recurrent laryngeal nerve before awake fiberoptic intubation.[2]Figure 1: (a) Midline, transverse orientation of ultrasound probe. Evaluation of trachea deep to the cricothyroid membrane. The hyperechoic structure is the air–muscosal interface, along with subsequent artifact deep to it. (b) Midline, transverse orientation of ultrasound probe. By translating the probe slightly, the thyroid (Thy) can be visualized, in this case with microcystic nodules. Under live evaluation, the esophagus can also be appreciated deep to the tracheaAfter evaluation of the cricothyroid membrane, a caudal translation of the probe allows for evaluation of the thyroid gland found on either side of the trachea. As seen in [Figure 2], the tracheal cartilage can be visualized at this location. The thyroid gland is also visualized, which in this case has evidence of benign microcystic nodules. At last, although it is difficult to clearly visualize on a still image, the esophagus can be found deep and most often to the left of the trachea. During direct visualization, the esophagus can be better appreciated by asking the patient to swallow.Figure 2: (a) C6 cervical nerve root. (b) C5 cervical nerve root. (c) C7 cervical nerve rootMoving on from the midline of the neck, as the ultrasound probe is directed laterally from the cricoid cartilage, the low cervical nerve roots can begin to be visualized. While the cricothyroid membrane often corresponds to the C6 level, there is some variability between patients and so these landmarks should be used only as a general guide. The C6 transverse process should have a significantly protuberant anterior tubercle, commonly known as Chassaignac tubercle. This tubercle is found just lateral to the carotid artery, with the C6 nerve root situated between the anterior and posterior tubercles and the vertebral artery deep to the bony structure. This view is important for several reasons. Selective blockade of the C6 nerve root can be performed here. In addition, the C6 level is also a common location to perform stellate ganglion block. The stellate ganglion is the confluence of the inferior cervical and superior thoracic sympathetic ganglia and provides sympathetic output to the head, face, neck, and upper extremities. Indications for a stellate ganglion block included complex regional pain syndrome, facial pain, as well as other issues such as herpes zoster pain or persistent ventricular tachycardia. There are several reasons why C6 is a popular level for the stellate ganglion block including that Chassaignac tubercle provides a clear landmark and the vertebral artery is deep to the bony structure and is thus less likely to be accidentally accessed. The target location for the stellate ganglion block is just above the longus colli muscle, which lays directly medial to the Chassaignac tubercle. The approach of the block needle is often lateral to medial using an in-plane approach or anterior to posterior with an out-of-plane approach.[3] In scanning more cephalad from the C6 vertebral level, the C5 vertebral body and the nerve root come into view. Similarly, there is an anterior and posterior tubercle, with anterior tubercle slightly higher than posterior. The lack of a protuberant anterior tubercle at C7 is often the differentiating factor when determining the cervical levels. The C5 nerve root can be found between the two tubercles, and the vertebral artery is again deep to the bony structure.[4] To visualize the C7 vertebral body, the ultrasound will need to be translated caudally. At the C7 level, the nerve root lies just anteromedial to the transverse process, without clearly defined tubercles. Of note, the vertebral artery emerges from the transverse foramen that was protecting it at the C2–C6 levels and lies just anterior and superficial to the transverse process of C7. It can be visualized just medial to the C7 nerve root.[4] Next, by moving the ultrasound probe to the mid-sternocleidomastoid location in the cranial–caudal dimension and focusing on the lateral–posterior border of the sternocleidomastoid muscle, the cervical plexus can be evaluated. It can be difficult to visualize the superficial cervical plexus, but a deposition of local anesthetic just lateral and superficial to the sternocleidomastoid should provide an adequate blockade of this plexus. Common indications for a cervical plexus block include central line placement in the internal jugular vein, head-and-neck procedures spanning from the earlobe to the clavicle, lymph node dissections, and carotid endarterectomies.[5] Additional anesthesia to deeper structures can be achieved with an intermediate cervical plexus block, which requires the infiltration of local anesthetic deep to an investing fascial layer, and typically travels along the deep border of the sternocleidomastoid muscle toward the carotid artery.[5] This is highlighted by the area shaded in blue in [Figure 3]. The anterior and middle scalene muscles are visualized deep to this investing fascial layer, and it is important to avoid an intramuscular injection of the local anesthetic, which would limit the efficacy of the block. Some cervical nerve roots can be seen between the two scalene muscles, but a true interscalene view is achieved at a slightly caudal location[6] [Figure 4].Figure 3: Superficial and intermediate cervical plexusFigure 4: Interscalene view, lateral to midline and cephalad to supraclavicular view. Able to visualize “traffic light” with C5 nerve root the most superficial and bordered by the anterior scalene (anteromedial) and middle scalene (posterolateral) muscles. Carotid artery visualized mediallyIn conclusion, starting from a familiar location, such as midline, can make even challenging ultrasound imaging, such as anterior neck, simple to identify. Understanding differences in the anatomy of anterior and posterior tubercles of cervical transverse processes is the key in identifying the cervical nerve root level.
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Dec 26, 2023
L. B. Mitrofanova + 5
Open Access