This level has a close relationship to the oral cavity. As such, lymphatic and vascular conditions of the floor of mouth and submandibular gland demonstrate mass lesions in this area. Although it is rare for thyroid carcinoma to metastasize to level I, in the survey of the neck with ultrasound, this region should still be examined. Lymph nodes are commonly enlarged in level I and into the neighboring level II, especially the jugulodigastric node which is ju st cranial and superficial to the carotid bulb (Fig. 11.2). It may be considered in the posterior aspect of zone I or in the cranial portion of level II. Its name derives from the fact that it is located at the place where the posterior belly of the digastric muscle passes over the IJV. While present in most individuals, this commonly hypertrophied lymph node is particularly notable in adolescents and young adults who have experienced recent episodes of tonsillopharyngitis.

Level II is the most common location for a number of lesions which often cannot be differentiated from one another on physical examination alone. As mentioned previously, the jugulodigastric lymph node is commonly palpated and demonstrated with ultrasound. Usually, sonography demonstrates an appropriate hilum with corresponding hilar vascularity on Doppler both of which suggest likely nodal hypertrophy. A cystic lesion in level II, especially in children and young adults, suggests a possible second branchial cleft cyst [7, 8] in the differential. Fine-needle aspiration cytology is useful to make differential determinations. However, any cystic node in the head and neck must be suspect for metastatic lymphadenopathy (Fig. 11.9). The most common primary origin of a cystic carcinomatous node in level II might be tonsil or tongue base squamous cell carcinoma. Alternatively, thyroid papillary carcinoma can also present as a cystic mass in the neck and even as a solitary mass in level II (Figs. 11.10 and 11.11). The key is to both examine the entire thyroid gland with ultrasound and add thyroglobulin washout to the needle assay of the cystic fluid.

A solid mass in level II may displace the carotid artery into an anterior location. In this circumstance, a lesion of neurogenic origin should be suspected [9, 10]. The cervical plexus or sympathetic chain may be the source of this type of lesion (Fig. 11.12). If a Horner’s syndrome is identified, the lesion is most likely to have originated from the sympathetic autonomic system (Figs. 11.13 and 11.14). If the patient has hoarseness and a vocal cord paralysis, the lesion may have originated from the vagus nerve. In circumstances where a mass resides at the carotid bulb and separates the internal and external carotid arteries, a carotid body tumor or paraganglioma would be realistic considerations [11] (Fig. 11.15). In this circumstance, Doppler demonstrates both the intense vascularity of the mass which is not noted in a schwannoma [12] (Fig. 11.16). The vascular supply to the mass is actually from the ascending pharyngeal artery branch off the external carotid, which can be seen in the lateral Doppler image in this sagittal image (Fig. 11.17). Although none of these lesions are malignant, it is important to understand how to separate them from the more life-threatening clinical conditions.

This region along with level IV is most often associated with conditions relative to the thyroid gland. Although exceedingly rare, lateral aberrant thyroid tissue [13] may be misinterpreted as the more common metastatic lymphadenopathy (Fig. 11.18). These lesions are separate from the main thyroid gland and are homogeneous and more rounded in structure than a lymph node. However, in the context of a mass lesion adjacent to the thyroid gland which is suspect for metastasis, a thyroglobulin washout would be recommended in addition to cytology. If the cytology is benign, no mass lesion of the thyroid gland is identified, and the thyroglobulin is positive; one still must suspect this as a metastatic node from an occult papillary thyroid carcinoma . A formal excision of the mass will be required and in this rare circumstance would confirm this lesion as benign thyroid tissue.

Patients with recurrent suppurative thyroiditis , especially left sided, may actually have a congenital fourth branchial cleft cyst or fistula which extends from the apex of the piriform sinus ending in the thyroid parenchyma [14, 15] (Fig. 11.19). Episodes may actually begin in children as young as 3 months and present as recurrent retropharyngeal abscess. Neck ultrasound may reveal an inflammatory process overlying the thyroid cartilage in addition to the changes in the adjacent thyroid gland (Fig. 11.20). In some cases, an actual fistulous tract can be identified.

The esophagus is an easily recognizable structure deep to the left lobe of the thyroid gland and adjacent to the trachea. Both the muscular and mucosal layers can be identified in the normal state. A Zenker’s diverticulum is a mucosal hernia between the cricopharyngeus and inferior constrictor muscles allowing a pouch to form which traps food and fluid [16–18]. It may be mistaken for a mass lesion. The sonographic features are loss of the usual concentric layers, some enlargement of the apparent esophageal structure, and internal, refractile debris (Figs. 11.21 and 11.22). Either on cine loop or sequential post-swallow static images, the debris often evacuates to some degree. Of course, the ultrasound is simply a means to suspect this lesion, and esophagram is the definitive required imaging study.

Finally, patients with primary hyperparathyroidism can have the source localized with ultrasound. Usually enlarged single hypoechoic lesions suggestive of an adenoma or multiple lesions indicating diffuse hyperplasia in the central neck (level VI) are self-explanatory. When this is noted in the context of hypercalcemia , there is very little confusion about what the images represent. However, a level III nodule in a patient with primary hyperparathyroidism may represent an ectopic parathyroid adenoma (Figs. 11.23 and 11.24). The differential diagnosis always includes lymphadenopathy. The vascularity of a parathyroid adenoma [19] differs from that of a lymph node (Figs. 11.25 and 11.26), and the absence of lymphocytes on aspiration cytology suggests that the lesion is unusual. Parathyroid cytology is notoriously difficult, but an aspirate for PTH will identify the lesion as ectopic parathyroid. Certainly a serum calcium and intact PTH would give an accurate biochemical diagnosis.

Any mass or cystic structure in level IV is suspect for metastatic thyroid carcinoma. The thoracic duct usually enters the venous system on the left side at the posterior junction of the internal jugular and innominate veins. Due to this special anatomical relationship, metastatic malignancy can be identified in this location, especially arising from adenocarcinomas whose origin is from structures below the clavicle. More specifically, the gastrointestinal tract from esophagus to colon may send malignant cells through the thoracic duct to the neck. In addition, other abdominal and pelvic primary tumors such as pancreatic and testicular cancer can produce the same metastatic result. Metastatic squamous cell carcinoma in addition to thyroid cancer should be suspected, especially in adults, when a partially or completely cystic mass is identified in the upper, mid-, or lower jugular chain [20] (Figs. 11.9 and 11.27).