Ultrasound Anatomy of the Head and the Neck

Abstract

The detection of pathological neck masses using ultrasound requires excellent familiarity with the physiological anatomy of the neck. Therefore this chapter presents the neck regions of the healthy individual, including the medial and the lateral neck compartments, the salivary glands, and the pharynx and larynx.

3.1 General Notes

The correct interpretation of ultrasound findings requires an excellent knowledge of the neck anatomy. Thus, an anatomic atlas should always be available in case of unknown findings. Furthermore, the examiner should be familiar with the sonographic appearance of the normal neck structures, which are often used as landmarks to facilitate the reproducibility of ultrasound findings by different examiners. These structures or landmarks include organs (such as the thyroid or salivary glands), bony structures or cartilages, muscles, blood vessels, and nerves. The purpose of this chapter is to present these structures in the healthy neck.

3.2 Settings of the Ultrasound Device and Starting the Examination

Normally we prefer a linear scanner with a frequency between 7.5 and 10 MHz. If postoperative scar formation of the neck tissue is present, the use of a lower frequency is necessary. Additionally, sector imaging is sometimes advantageous, especially if large structures should be described.

The neck examination should always start with an area where the device adjustment can be checked [1]. We prefer starting the examination with a view of the thyroid gland and the surrounding vessels, i.e., the common carotid artery and internal jugular vein (Fig. 3.1). In this section, the carotid artery wall shows a high echogenicity, whereas the lumen of the vessels should be hypoechoic (Video 3.1). The quality of the thyroid’s echo is between the echogenicity of both structures. This section through the thyroid gland allows fast and easy adjustment of the device. Then we examine the medial neck compartment, followed by both lateral compartments. After this, the region of the salivary glands is examined, followed by the tongue and the tongue base.

Fig. 3.1

Basic adjustment of the ultrasound device using a standardized plane through the thyroid gland (THY), the common carotid artery (CCA), and the internal jugular vein (IJV). SCM sternocleidomastoid muscle, SHM sternohyoid muscle, STM sternothyroid muscle, TR trachea, VN vagal nerve

3.3 Systematic Head and Neck Ultrasound Examination: Normal Findings

3.3.1 The Medial Neck Compartment, Thyroid, and Larynx

The thyroid is the main organ in the medial neck compartment (Video 3.2). The thyroid lobes are connected by the isthmus, which can be seen in both transverse and sagittal section (Figs. 3.2 and 3.3). The thyroid of the healthy patient is more or less homogenous, and its echogenicity is similar to the echogenicity of the large salivary glands [1, 2]. The tracheal cartilages can also be seen, producing artificial reverberation echoes (Fig. 3.2). Lateral to the thyroid , the large blood vessels (the common carotid artery and more laterally, the internal jugular vein) can be found (Fig. 3.4). Sometimes, the vagal nerve becomes visible next to the blood vessels (Fig. 3.1). In the depth, the thyroid adjoins the scalene muscles and the vertebral column. Infrahyoid muscles can be seen in front of the thyroid gland. Differentiation of the infrahyoid muscles would be possible without any problem when using a modern ultrasound device.

Fig. 3.2

Lower medial cervical compartment with the homogenous thyroid gland (THY), transverse plane. CCA common carotid artery, IST isthmus, TR trachea

Fig. 3.3

Isthmus of the thyroid (IST), sagittal plane. TC tracheal cartilage, TR tracheal lumen

Fig. 3.4

Left thyroid lobe area, transverse plane (left) and sagittal plane (right). CCA common carotid artery, SHM sternohyoid muscle, SM scalene muscles, STM sternothyroid muscle, THY thyroid gland, VC vertebral column

The upper esophagus (Fig. 3.5) can commonly be seen under the left thyroid lobe, next to the vertebral column [3]. Parts of the esophagus are covered by the acoustic shadow of the trachea. The esophagus is characterized by an onion-like pattern. Especially in the sagittal plane, swallowing of saliva can be observed (Video 3.3). Sometimes, the esophagus also can be seen under the right thyroid lobe (Fig. 3.6); in rare cases, the esophagus cannot be seen at all, because it can be completely covered by the acoustic shadow of the trachea.

Fig. 3.5

Esophagus (ES) dorsal to the left thyroid lobe (THY), in transverse plane (a) and sagittal plane (b). CCA common carotid artery, IJV internal jugular vein, SCM sternocleidomastoid muscle, TR trachea, VC vertebral column

Fig. 3.6

Esophagus (ES) next to the right thyroid lobe (THY). CCA common carotid artery, TR trachea

The cricoid and thyroid cartilages can be seen cranial to the thyroid (Figs. 3.7 and 3.8). In younger patients, the cartilages are not ossified, which allows a sonographic view into the larynx. Then structures such as the vestibular folds can be examined (Video 3.4). With increasing ossification, the examination of intralaryngeal structures becomes more and more difficult, but not impossible [4].

Fig. 3.7

Cricoid cartilage (CC). SHM sternohyoid muscle, STM sternothyroid muscle

Fig. 3.8

Transverse (a) and sagittal (b and c) sections through the larynx at the level of the thyroid cartilage (TC). IHM infrahyoid muscle, SHM sternohyoid muscle, STM sternothyroid muscle, THM thyrohyoid muscle, VF vestibular fold

3.3.2 The Jugular Fossa and the Supraclavicular Region

In clinical practice, it is often forgotten to examine the jugular fossa and the supraclavicular region, because most diseases of the head and neck become clinically apparent more cranially. Nevertheless, we have often found metastatic lymph nodes in this area, especially in patients suffering from thyroid cancer, breast cancer, or even colon or prostate cancer. Furthermore, the sonographic examination of the jugular fossa allows a view into the upper mediastinum, where, for example, parathyroid adenomas can be found.

In young patients, parts of the thymus can be seen in the jugular fossa (Fig. 3.9). Likewise, in this area, blood vessels often can be seen in healthy patients. Thus, sometimes, the aortic arch becomes visible (Fig. 3.10). Furthermore, the brachiocephalic artery, the supraclavicular artery, and the common carotid artery can be detected next to the pleura (Figs. 3.11 and 3.12). At last, in this area, the nerves of the cervical plexus can be seen well between both scalene muscles (Figs. 3.13 and 3.14), allowing ultrasound-guided plexus anesthesia.

Fig. 3.9

In children, the thymus can be detected in the upper mediastinum through the sternum (a) and sometimes also through the jugular fossa (b). AO aorta, CL clavicle

Fig. 3.10

The jugular fossa with the arch of the aorta (AO). (a) B-Scan and color-coded sonography. (b) Doppler sonography

Fig. 3.11

Right supraclavicular region with the brachiocephalic artery (BA) and its bifurcation; the arrow indicates a calcified plaque. CCA common carotid artery, SA supraclavicular artery

Fig. 3.12

Right supraclavicular region, transverse plane (left) and sagittal plane (right). CL clavicle, IJV internal jugular vein, SA supraclavicular artery

Fig. 3.13

Left supraclavicular region with parts of the supraclavicular plexus (arrows). CL clavicle, PL pleura, SA supraclavicular artery

Fig. 3.14

Parts of the cervical plexus (asterisk) can be seen between the anterior scalene muscle (ASM) and the posterior scalene muscle (PSM)

3.3.3 The Lateral Neck Compartment

The examination of the lateral neck compartments starts with the general view through the appropriate thyroid lobe, the large blood vessels, and the sternocleidomastoid muscle (Fig. 3.15). Too much pressure with the array on the patient’s neck results in a collapse of the internal jugular vein. In contrast to the common carotid artery, the wall of the vein is very thin, and sometimes venous valves can be detected (Fig. 3.16; (Video 3.5). The external jugular vein can be seen in the superficial area of the lateral neck (Fig. 3.17). The omohyoid muscle (Fig. 3.18) is characterized by an oblique course in this area. This muscle is located between the sternocleidomastoid muscle and the large vessels and can easily be misdiagnosed as a lymph node in this area.

Fig. 3.15

Lateral cervical compartment. (a) Transverse plane. (b) Sagittal plane. CCA common carotid artery, IJV internal jugular vein, SCM sternocleidomastoid muscle, SHM sternohyoid muscle, STM sternothyroid muscle, THY thyroid, VN vagal nerve

Fig. 3.16

Venous valve (arrow) in the left internal jugular vein (IJV)

Fig. 3.17

External jugular vein (EJV)

Fig. 3.18

The omohyoid muscle (OHM) can be seen in an oblique plane under the sternocleidomastoid muscle (SCM). CCA common carotid artery, IJV internal jugular vein

More cranially, the bifurcation and the jugulofacial vein angle become obvious (Fig. 3.19). The relation of both structures to each other differs. Often it is necessary to differentiate between the large arteries of the neck. A differentiation is possible using Doppler ultrasound. The color-coded examination and the Doppler examination of the common carotid artery are easy (Fig. 3.20, Video 3.6). In contrast, the detection of the internal and the external carotid artery is more difficult, especially if the bifurcation is more cranial. Depending on the anatomy of the bifurcation, the internal and external carotid arteries can be seen in a more sagittal plane or a frontal plane (Fig. 3.21). The pulsed-wave (pw) Doppler allows a distinction between both blood vessels (Video 3.7). Whereas the end-diastolic pressure is nearly zero in the external carotid artery, it is much higher in the internal carotid artery (Fig. 3.22).

Fig. 3.19

Carotid bulb, bifurcation (BIF) and jugulofacial vein angle (JVA) in a transverse view (a, b, different patients) and a sagittal (c) view. FV facial vein, IJV internal jugular vein, SCM sternocleidomastoid muscle

Fig. 3.20

Common carotid artery (CCA). (a) B-scan. (b) Color-coded sonography. (c) Doppler sonography

Fig. 3.21

Carotid bifurcation with a calcified plaque (arrow). (a) B-scan. (b) Color-coded sonography. CCA common carotid artery, ECA external carotid artery, ICA internal carotid artery

Fig. 3.22

Doppler sonography of the external carotid artery (ECA) (a) and internal carotid artery (ICA) (b)

If the probe is moved laterally in a sagittal view, the vertebral artery can be detected (Fig. 3.23). Its lumen is frequently covered by the acoustic shadows of the transverse processes of the vertebra (Videos 3.8 and 3.9).

Fig. 3.23

Vertebral artery (VA) and vertebral vein (VV) in a sagittal section. (a) B-Scan. (b) Color-coded sonography. (c) Doppler sonography. TP transverse process of the vertebra

3.3.4 The Floor of the Mouth, Including Submandibular and Sublingual Glands

Cranial to the bifurcation and the jugulofacial vein angle, the submandibular gland can be detected (Fig. 3.24). In healthy persons, the gland is homogeneous, and the echogenicity is similar to that of the thyroid gland (Video 3.10). The submandibular gland has direct contact with the inferior part of the parotid gland, and the echo of the two glands is somewhat different (Fig. 3.25). Within the submandibular gland, the hilus can sometimes be seen; it should not be confused with intraglandular vessels (Fig. 3.26). The facial artery also can be detected in this region (Fig. 3.27).

Fig. 3.24

Oblique section through the jaw angle. SM submandibular gland, TO tongue

Fig. 3.25

Contact between submandibular gland (SM) and parotid gland (PAR). LN lymph node, TO tongue

Fig. 3.26

A hilus-like structure (asterisk) in the submandibular gland (SM), diagnosed as an intraglandular blood vessel by using color-coded ultrasound

Fig. 3.27

The facial artery (FA) can be detected upon the mandible (MA) and next to the posterior end of the submandibular gland (SM). PAR parotid gland

From the submandibular gland, the array should be moved in the direction of the mouth floor (Video 3.11). In the ventral portion of the mouth floor, a figure like the “head of Mickey Mouse” can be seen (Fig. 3.28). The single muscles of the mouth floor can be identified as structures of poor echo (Figs. 3.28 and 3.29). Furthermore, the sublingual glands can be seen beside the mandible. They are characterized by the typical echo similar to that of other major salivary glands. Finally, the sublingual artery can be seen with B-scan and with color-coded sonography (Fig. 3.30).

Fig. 3.28

Frontal section through the anterior mouth floor (a) and posterior mouth floor (b). DIG digastric muscle, GHM geniohyoid muscle, MA mandible, MHM mylohyoid muscle, SL sublingual gland

Fig. 3.29

Sagittal section through the mouth floor. The arrows mark the tongue surface. GGM genioglossus muscle, MA mandible, MF mouth floor

Fig. 3.30

Frontal section through the mouth floor; color-coded sonography detects both sublingual arteries. DIG digastric muscle, GHM geniohyoid muscle, MHM mylohyoid muscle

3.3.5 Tongue, Tongue Base, and Tonsils

Although the tongue (Video 3.12) can also be seen in a frontal section, the optimal visualization of its whole body requires a sagittal view (Fig. 3.31). In this view, the caudal parts of the tongue base can also be identified (Video 3.13). Within the tongue base, a small area is always covered by the acoustic shadow of the hyoid (Fig. 3.32), and the examiner should be aware that pathological changes of this region can be overlooked.

Fig. 3.31

Sagittal view of the tongue body (TO), MF mouth floor

Fig. 3.32

Sagittal view of the tongue base (TO). MF mouth floor, HY hyoid

The tonsillar region can be seen with an oblique section through the submandibular gland (Fig. 3.33). The tonsils are located next to the tongue and the dorsal part of the submandibular gland [5]. A sonographic differentiation between small tonsils in adults and status after tonsillectomy is often impossible. Compared with adults, in children the tonsils can appear very imposing.

Fig. 3.33

Right and left tonsillar region (TS); SM submandibular gland, TO tongue

3.3.6 The Parotid Gland and the Cheek

As mentioned before, the parotid gland can be detected next to the submandibular gland. Thus, the array has only to be moved dorsally until the mastoid can be seen. Then, the anterior part of the array must be raised over the mandible to get the standard view of the parotid gland (Fig. 3.34). In the depth, the retromandibular vein can be seen; it divides the gland into a superior and a deep portion (Fig. 3.35). The anterior parts of the gland can be detected if the examiner follows the glandular tissue above the masseter (Fig. 3.36). While the patient bites firmly, a thickening of the masseter can be detected impressively (Fig. 3.37). Similar to the other major glands, the Stensen duct can only be seen in pathological situations. Anterior to the masseter, the cheek and the teeth become visible (Fig. 3.38).

Fig. 3.34

Transverse (a) and frontal section (b) through the parotid gland (PAR). MA mandible, MM masseter muscle

Fig. 3.35

The retromandibular vein (RMV) divides the parotid gland (PAR) into a superficial portion and a deep portion. MA mandible

Fig. 3.36

Transverse section through the masseter muscle (MM). MA maxilla, PAR parotid gland

Fig. 3.37

Masseter muscle (MM) during relaxation (left) and during biting (right). MA maxilla

Fig. 3.38

Anterior cheek, transverse plane. MA maxilla, MM masseter muscle, T teeth