Neck

Technique

Both computed tomography and magnetic resonance imaging can be used to a great advantage to demonstrate all structures of the neck. Intravenous contrast is needed to better demonstrate tumor extension and to separate the neck vessels from lymph nodes on computed tomography. Magnetic resonance imaging can image the neck in any plane and does not necessitate the use of intravenous contrast.

Anatomy

The soft tissues between the base of the skull and the mandible down to the thoracic aperture along the cervical spine forms the neck. The neck can be divide into three compartments, the anterior visceral compartment containing the larynx and the hypopharynx in the upper half and the trachea, oesophagus, the thyroid and the parathyroid glands in the lower half. The neurovascular bundles together with the stemocleidomastoid muscles are found lateral to the visceral compartment. The cervical spine

Figure 27. Second branchial cleft cyst - computed tomography A large cystic expansion is seen in front of the sternocleidomastoid muscle with an extension in towards the hypopharynx. along with the supporting muscles make up the posterior third compartment (Fig. 25 a-d).

Pathology

Branchial cysts are of congenital origin and originate out of pharyngeal pouches in connection to the branchial clefts. The most common is the second branchial cleft cyst found in front of the stemocleidomastoid muscle below the level of the hyoid bone (Fig.27). The cyst can be connected to the skin or the pharynx through a fistulous tract. The cyst often become symptomatic in adolescence after they have become infected. The first branchial cleft can also give rise to a cyst in the preauricualr area. Computed tomography and magnetic resonance imaging will easily demonstrate these lesions in typical location having cystic characteristics.

A thyroglossal duct cyst can also be found in the midneck. The cyst is then situated just off the midline on the outside of the one of the thyroid lamina.

Cystic hygroma is the most common congenital lesion of the neck often originating in the supraclavicular fossa and extending down into the mediastinum as well as up into the neck. A hygroma consists of dilated malformed lymphatic vessels and infiltrate diffusely between the muscle bundles of the neck also extending posterior to the stemocleidomastoid muscle. Large tumors will also lead to compression and narrowing of the upper airway.

Lymphadenopathy in the neck often reflects an underlying malignancy. Computed tomography and magnetic resonance imaging can verify these enlarged lymph nodes and also demonstrate lymphadenopathy in areas difficult to assess by clinical examination as well as demonstrate the primary. Squamous cell carcinomas originating in the nasopharynx, tonsil, base of the tongue or the pyriform sinuses are the most common reasons for lymphadenopathy which can be clinically of unknown origin. Lymph nodes having a short axis diameter of more than 1 -1.5 cm are to be considered enlarged (Fig 22). Metastatic lymph nodes often have an enhancing rim around a more necrotic centre on contrast enhanced computed tomography. Metastases can also be seen as local defects in the periphery of homogeneously enhancing nodes. Tuberculosis can also have similar appearing lymphadenopathy. Lymphoma in the neck is often of the non-Hodgkin variety and more often present with homogenous lymph nodes in large numbers and of varying sizes.

Parapharyngeal tumors

Parapharyngeal tumors are detected as a bulging asymmetry of the lateral pharyngeal wall or as a mass behind angle of the mandible. Computed tomography or magnetic resonance imaging can delineate the parapharyngeal space and detect smaller tumors which are difficult to assess clinically and often suggest the origin of most of these tumors which is of importance for the surgical approach.

The lateral border of the parapharyngeal spaces made up of the mandible, the parotid gland and further down of the stemocleidomastoid muscle while the lateral pharyngeal wall makes up the medial border. The styloid process divides the space into an anterior and a posterior compartment. In the anterior compartment one finds tumors originating out of the deep portion of the parotid gland or from an accessory salivary gland. The majority of these tumors are benign mixed tumors although malignant parotid tumors are also possible. Tumors in the posterior compartment along the neurovascular bundle will displace the styloid process and musculature arising from the styloid process anteriorly. The two most common tumors along the neurovascular bundle are schwannomas and paragangliomas. Schwannomas are most often associated with the vagal nerve extending up towards the jugular foramen while paragangliomas originate out of the ganglion nodosum of the vagus nerve (glomus vagale ). Both these tumors enhance on computed

tomography and can be difficult differentiate. External carotid angiography can separate the highly vascular paranganglioma from the poorly vascular schwannoma (Fig. 28 a-b). Magnetic resonance imaging can often also separate these two tumors types by showing a characteristic pattern of vascular flow phenomena in the paragangliomas.

Sven G. Larsson and Anthony A. Mancuso