Authors: Kinga Karlinger, Erika Márton
11. Head and neck imaging Author: Péter Magyar Author: Péter Magyar
11.2. Radio-anatomy of the head and neck
The diversity of pathology of the head and neck region is due to its very complex anatomy.
The head and neck region encompasses tremendous spectrum of tissues in a compact space.
Understanding both this special anatomic region with its normal tissue content and the scope of pathologic entities are the basis of the accurate assessment of a lesion in head and neck.
Head and neck section can be divided into clinically important subregions: 1) skull base; 2) orbit; 3) temporal bone; 4) paranasal sinuses; 5) facial bones; 6) floor of the mouth; 7) neck (supra- and infrahyoid) and 8) thoracic aperture.
The level of the hyoid bone is an important border in the neck section, that separetes the suprahyoid neck compartment from the infrahyoid neck compartment.
Significance of the neck compartments: Recognition of the compartment in which a lesion is located is the basis of the adequate radiological evaluation of a lesion. This table summarizes both the suprahyoid and infrahyoid neck compartments. Those spaces that cross the entire length of the neck are in Italic.
Suprahyoid neck compartments
pharyngeal mucosal space (visceral space)
parapharyngeal space (prestyloid compartment)
parotid space
masticator space
sublingual space
submandibular space
buccal space
retropharyngeal space
Danger-space
perivertebral space
carotid space (poststyloid compartment)
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Infrahyoid neck compartments
anterior cervical space
posterior cervical space
visceral space
retropharyngeal space
Danger-space
perivertebral space
carotid space (poststyloid compartment)
Orientation is further helped by the central localization of the parapharyngeal space, which is named as ―compass of the suprahyoid neck compartment‖. Danger space - found behind the retropharyngeal space - is bounded superiorly by the skull base, anteriorly by the alar fascia and posteriorly by the prevertebral fascia. It comes to an end at the level of the diaphragm. It gets its common name from the risk that an infection in this space can spread directly to the thorax.
Knowledge of the head and neck lymph node chains and the usual modes of spread of diseases is essential for accurate assessment of a head and neck malignancy or inflammatory process. Cervical lymph nodes are divided into six levels. Characteristics of the lymph nodes such as size (shorter diameter < 10 mm), shape (oval), and structure (cortical-hilar
differentiation) have to be evaluated. In lymphadenitis (which is the most common cause of palpable neck mass in children), the lymph nodes become enlarged, but the echogenic fatty hilum and the thin hypoechoic cortex can be differentiated. However, in malinancy, the enlarged lymph nodes become hypoechoic, round, with loss of structure and cystic or necrotic degeneration in many cases.
11.3. Imaging modalities
11.3.1. Radiography (noncontrast and contrast)
Paranasal sinus radiography provides information about the air-content of the frontal and maxillary sinuses. Air-fluid level or decreased transparency in the paranasal sinuses suggests abnormality.
Facial bone radiography and orbit radiography can detect radiopaque foreign bodies and major fractures of the orbital walls; however, the part played by conventional radiography has decreased significantly with the widening availability of CT.
Conventional x-ray films (Stenvers and Schüller views) are capable of detecting ear disease with concomitant large bony destructions or deareation of the mastoid cells. However, for more subtle ear pathology CT or MRI is the modality of choice.
Lateral neck radiograph can evaluate thyroid enlargment by demonstrating tracheal narrowing or tracheal dislocation.
Dental panoramic radiograph of the teeth (Orthopantomogram) is used in everday practice, and its most common indication is to determine the status of wisdom teeth and trauma to the jaws. Radiopaque sialolith can be also discovered by this modality.
133 Swallow study is used to diagnose pathology in the pharynx and esophagus. It can be
performed with barium in patients with dysphagia, pain on swallowing and mass lesions, or with iodine in perforation and in clinically suspected postoperative leakage.
Sialography – a radiographic examination of the salivary glands and associated ducts following the injection of a radiographic contrast media - is helpful in suspected cases of ductal stricture, calculi or sialectasia.
11.3.2. Angiography
Digital subtraction angiography (DSA) is a type of fluoroscopy technique - using ionizing radiation - to clearly visualize blood vessels of the neck in a bony or dense soft tissue environment. Advantage of the DSA – beside its excellent diagnostic value - that it allows therapeutic interventions. Intravenous iodine administration is contraindicated in contrast allergy and renal impairment. In neck, it excels in the diagnosis and treatment of carotid artery stenosis. Chemotherapy and embolization of tumors can be applied as well.
11.3.3. Ultrasonography
Most of the soft tissues in head and neck can be easily evaluated by ultrasonography. These examinations are performed with high-resolution 7-13 MHz linear array transducer, which have 3-5 cm penetration. The advanatages of US include good availability, multiplanar visualization, repeatable (no ionizing radiation), fast, and it provides real-time imaging.
Postoperative sutures, tracheostoma and former irradiation of the neck make US examination more difficult.
Superficial soft tissues such as floor of the mouth, salivary glands, surrounding structures of the cervical visceral region, buccal, occipital and supraclavicular regions can be evaluated by B-mode ultrasonography. In the neck, thyroid gland, carotid and jugular vessels and lymph nodes can be examined by US. US can determine whether a mass is cystic or solid, and therefore able to differentiate between cellulitis and abscess. Superficial bony destruction of the mandible and facial bones can be evaluated by US. With Doppler function, direction and velocity of flow in neck vessels can be determined. Doppler-US also can provide information about the vascularisation of a neck mass.
Ultrasound-elastography is a newly developed imaging technique for the reconstruction of tissue stiffness by measuring the degree of tissue's deformation in response to the application of an external force. It provides information about solid and cystic masses, and can give help in biopsy planning by demonstrating the optimal site for puncture.
Contrast-enhanced US is not part of the diagnostic modalities used routinely; however, it is capable of demonstrating vascularity, enhancement pattern and cystic or necrotic areas of a mass.
11.3.4. Computed Tomography
CT has several advantages over traditional 2D medical imaging: provides cross-sectional imaging; eliminates the superimposition of images of structures outside the area of interest;
provides good soft tissue resolution when intravenous contrast is administered; visualizes bony detail in complex fractures and bone destruction. Multidetector-row CT (MDCT) - with its submillimeter spatial resolution - is also capable of creating multiplanar reformatted imaging. Disadvantages of CT include high radiation-dose (which is approx. hundred times higher than that of conventional radiographs), and artifacts related to dental fillings.
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Paranasal CT – nowdays - is performed in supine position, which constructs primarily axial images. Coronal view – which has similar appearance to sinus radiography - can be later digitally reconstructed. Earlier, CT was performed in a position to primarily get the coronal view; however, the quality of this technique was not satisfactory due to artifacts caused by metal-containing dental fillings. Noncontrast paranasal CT plays important role to assess more complicated, recurrent disorders, e.g. chronic sinusitis. Contrast-enhanced paranasal CT is a helpful imaging tool in soft tissue evaluation, e.g. in inflammation and tumours. However, in these cases, MRI provides an even better soft tissue resolution.
HRCT excels in the evaluation of air spaces and fine bone structures - including hearing ossicles - of the temporal bone. HRCT is primarily performed at submillimeter intervals, which allows reconstructions in all three planes.
Noncontrast orbit CT has an important role in the assessment of orbital bony injuries and localization of foreign bodies.
Contrast-enhanced orbit CT – if MRI is not available – can be indicated in inflammation and tumours.
Contrast-enhanced head and neck CT (from the skull base to the aortic arch) can evaluate acute inflammation and tumours. It can be used for tumour staging; however, for that MRI is the first-line modality by providing better soft tissue resolution. One of the disadvantages of head and neck CT – especially in children - is the relatively high radiation dose to which the eye lenses are sensitive.
CT angiography is performed to evaluate neck vessels. Carotid arteries can be examined from aortic arch to skull base by bolus technique in arterial phase.
It is important to mention an emerging new technique: the cone-beam CT (CBCT). A CBCT scanner utilizes a 2D flat panel detector, and it can acquire the image of the whole volume in a single rotation around the patient. The scanning software collects the data and reconstructs it by a mathematical algorithm, producing 3D images. This method uses ten times less ionizing radiation than conventional CT, while provides all the same information. Length that can be imaged by CBCT is approx. 5-16 cm; however, C-arm equipments used in interventional radiology are also based on the cone-beam principles. CBCT’s advantages are the lower cost and smaller size, which make this technique increasingly important. CBCT can be used to visualize anatomical detail of paranasal sinuses, in dental imaging and implantology.
11.3.5. Magnetic Resonance Imaging
MR provides outstanding sensitivity for the discrimination of soft tissues; therefore it excels in the evaluation of inflammatory and tumorous processes. MRI examinations take longer time than CT studies; however, it can provide direct multiplanar imaging. One of the advantages of MRI is the lack of ionizing radiation; therefore it is the modality of choice in pregnancy and paediatrics. In trauma emergency, metallic foreign bodies and life support appliances can be a problem. CT is superior to MRI in the assessment of air space anatomy and cortical bone structure in detail.
In orbit, facial and head and neck MRI, T1, T2, fat-saturated and contrast-enhanced T1 sequences are the most popular imaging sequences, which can be taken primarily in all three orientations (axial, sagittal, coronal), depending on the clinical problem.
Head and inner ear MRI is recommended to evaluate pontocerebellar soft tissue processes.
MR angiography is a group of techniques - based on flow effects (phase-contrast MRI) or on contrast (gadolinium-enhanced MRI) - to image blood vessels.
135 11.3.6. Nuclear Medicine
Thyroid scintigraphy – the most frequently used neclear medicine technique in head and neck – is performed by utilizing radioactive iodine, and it is capable of assessing the physiologic function of the gland. The functional status of a thyroid nodule may be categorized as hyperfunctioning (hot nodule) and hypofunctioning (cold nodule). Hot nodules (which are typically adenomas) are more often benign than cold lesions. Malignancies usually appear as cold nodules, while cysts typically present as cold nodules.
Parathyroid scintigraphy is performed to localize parathyroid abnormalities (e.g. ectopic parathyroid adenoma) in patients with hyperparathyroidism.
Functional status of the salivary glands can be evaluated by salivary gland scintigraphy.
PET is a functional imaging modality based upon the distribution of a glucose analogue radioisotope (18F-fluorodeoxyglucose, FDG). In combination with either CT or MR imaging - which modalities provide morphological information -, PET has greatly increased the sensitivity and specificity in the evaluation of primary as well as recurrent malignancies, in tumour staging, and plays an important role in inflammatory processes.