Thorough knowledge of the complex anatomy of the head and neck is essential to understanding the ultrasonographic appearance of this region. The intimate familiarity with anatomic structures obtained by performing surgical procedures makes active radiographic imaging modalities like ultrasound especially suited for use by surgeons. An understanding of the normal sonographic appearance of head and neck structures is critical to recognizing abnormal pathology.
Ultrasound of head and neck: anatomy
Ultrasonography of the head and neck has been performed for decades, primarily by radiologists. Recent improvements in high-resolution ultrasound have made the technology much more accessible to clinicians. Office-based ultrasound allows clinicians to personally perform a real-time diagnostic radiographic procedure and literally see pathology below the skin. This ability makes ultrasound an important extension of the physical examination and enables clinicians to more rapidly and effectively treat patients.
A thorough knowledge of the complex anatomy of the head and neck is essential to understanding the ultrasonographic appearance of this region. The frequent performance of surgical procedures leads to a familiarity with anatomic structures that makes active radiographic imaging like ultrasound especially suited for use by surgeons. It is important to understand and appreciate the normal sonographic appearance of head and neck structures before recognizing abnormal pathology.
An ultrasound examination should follow a systematic and thorough course to ensure that all structures of the neck from clavicle to mandible are evaluated. The examination is usually performed in both the axial and longitudinal planes. In gaining experience, a beginning ultrasonographer typically develops a structured routine that ultimately leads to a comprehensive, yet expeditious, sonographic evaluation.
An appreciation of the basic physics and principles of ultrasound is important to be able to recognize the central characteristics of various tissue types. The sonographic appearance of fat is hyperechoic relative to muscle, which is hypoechoic. The cervical fascia that invests the muscles and organs of the neck is very echogenic and is seen clearly as a distinct white line that delineates structures from one another. Mucosa is also very echogenic and can be easily differentiated from the hypoechoic muscle that it typically overlies. Arteries are anechoic and pulsations can often be seen. Veins are also anechoic and easily compressible with pressure from the ultrasound probe.
Division of the neck into anatomic triangles based on the sternocleidomastoid, digastric, and omohyoid muscles, all of which are readily identified sonographically, creates easily recognizable landmarks on which to base a thorough examination. These triangles do not correspond exactly with the American Joint Committee on Cancer levels of the neck for cancer staging, but an examiner may do simple correlations using sonographic landmarks.
The triangular-shaped area anterior to the sternocleidomastoid muscle is anatomically classified as the anterior triangle, whereas the region posterior to the muscle is termed the posterior triangle. The anterior triangle is further divided into infrahyoid and suprahyoid sections. The anterior belly of the digastric muscle subdivides the suprahyoid portion into the submandibular triangle posteriorly and submental triangle anteriorly. Below the posterior belly of the digastric muscle, the infrahyoid triangle is divided into the muscular and carotid triangles by the superior belly of the omohyoid muscle.
Borders of the posterior triangle include the sternocleidomastoid muscle anteriorly, the occiput superiorly, the clavicle inferiorly, and the trapezius muscle posteriorly. The inferior belly of the omohyoid muscle subdivides the region into the occipital triangle superiorly and the supraclavicular triangle inferiorly.
Submental triangle (level 1a)
The anterior bellies of the right and left digastric muscles form the lateral borders of the submental triangle. The apex of the triangle is the mental symphysis, the base is the hyoid bone, and the mylohyoid muscle forms the floor. Lymph nodes are the only structures of note that reside in the submental space.
Visible via transverse imaging through the submental region are the extrinsic muscles of the tongue, including the genioglossus, geniohyoid, and hyoglossus muscles ( Fig. 1 ). The sling-shaped mylohyoid muscle forms the floor of the mouth.
The lingual artery courses medial to the hyoglossus muscle, whereas the submandibular duct runs alongside the sublingual gland between the hyoglossus and more superficial mylohyoid muscle. These muscles are readily distinguished from one another, and the hyoglossus muscle can be seen contracting when the patient’s tongue is moved from side to side during active ultrasonography, whereas the mylohyoid remains immobile. The hyperechoic sublingual gland is elongated and fills much of the lateral floor of mouth extending posteriorly from the submandibular gland toward the mental symphysis anteriorly. An abnormally dilated submandibular duct is easily seen sonographically in the floor of the mouth, but a normal duct is less evident. The duct is differentiated from the lingual artery and vein by the lack of flow on Doppler imaging.
Submental triangle (level 1a)
The anterior bellies of the right and left digastric muscles form the lateral borders of the submental triangle. The apex of the triangle is the mental symphysis, the base is the hyoid bone, and the mylohyoid muscle forms the floor. Lymph nodes are the only structures of note that reside in the submental space.
Visible via transverse imaging through the submental region are the extrinsic muscles of the tongue, including the genioglossus, geniohyoid, and hyoglossus muscles ( Fig. 1 ). The sling-shaped mylohyoid muscle forms the floor of the mouth.
The lingual artery courses medial to the hyoglossus muscle, whereas the submandibular duct runs alongside the sublingual gland between the hyoglossus and more superficial mylohyoid muscle. These muscles are readily distinguished from one another, and the hyoglossus muscle can be seen contracting when the patient’s tongue is moved from side to side during active ultrasonography, whereas the mylohyoid remains immobile. The hyperechoic sublingual gland is elongated and fills much of the lateral floor of mouth extending posteriorly from the submandibular gland toward the mental symphysis anteriorly. An abnormally dilated submandibular duct is easily seen sonographically in the floor of the mouth, but a normal duct is less evident. The duct is differentiated from the lingual artery and vein by the lack of flow on Doppler imaging.
Submandibular triangle (level 1b)
The submandibular triangle is bounded by the anterior and posterior digastric bellies inferiorly and the mandible superiorly. Forming the medial border of this triangle are the hyoglossus and mylohyoid muscles. The sublingual space lies deep to the mylohyoid muscle ( Fig. 2 ). The mylohyoid muscle is the key to determining whether or not pathology resides in the sublingual or submandibular space; a lesion deep to the mylohyoid arises from the sublingual space, whereas anything superficial to the muscle rests in the submandibular space.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
