Lesions Lymphangioma (Cystic Hygroma) Hemangioma Acute Sialadenitis Chronic Sialadenitis HIV‐Associated Lymphoepithelial Lesions Mucous Escape Phenomena Sialadenosis (Sialosis) Sialolithiasis Sjögren Syndrome Sarcoidosis Congenital Anomalies Salivary Glands First Branchial Cleft Cyst Neoplasms – Salivary, Epithelial Benign Pleomorphic adenoma Warthin tumor Oncocytoma Malignant Tumors Mucoepidermoid carcinoma Adenoid cystic carcinoma Neoplasms – Non‐Salivary Benign Lipoma Neurogenic tumors Malignant Lymphoma Metastases
Introduction
Anatomic and functional diagnostic imaging plays a central role in modern medicine. Virtually all specialties of medicine to varying degrees depend on diagnostic imaging for diagnosis, therapy, and follow‐up of treatment. Because of the complexity of the anatomy, treatment of diseases of the head and neck, including those of the salivary glands, is particularly dependent on quality medical imaging and interpretation. Medical diagnostic imaging consists of two major categories, anatomic and functional. The anatomic imaging modalities include computed tomography (CT), magnetic resonance imaging (MRI) and ultrasonography (US). Although occasionally obtained, plain film radiography for the head and neck, including salivary gland disease, is mostly of historical interest. In a similar manner, the use of sialography is significantly reduced, although both plain films and sialography are of some use in imaging sialoliths. Functional diagnostic imaging techniques include planar scintigraphy, single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance spectroscopy (MRS), all of which are promising technologies. Recently, the use of a combined anatomic and functional modality in the form of PET/CT has proved invaluable in head and neck imaging. Previously widely employed procedures including gallium radionuclide imaging are less important today than in the past.
Imaging Modalities
COMPUTED TOMOGRAPHY (CT)
Computed tomography (CT) has become indispensable in the diagnosis, treatment, and follow‐up of diseases of the head and neck. The latest generation of multiple‐row detector CT (MDCT) provides excellent soft‐tissue and osseous delineation. The rapid speed with which images are obtained, along with the high spatial resolution and tissue contrast, makes CT the imaging modality of choice in head and neck imaging. True volumetric data sets obtained from multi‐detector row scanners allow for excellent coronal, sagittal, or oblique reformation of images as well as a variety of 3D renderings. This allows the radiologist and surgeon to characterize a lesion, assess involvement of adjacent structures or local spread from the orthogonal projections or three‐dimensional rendering. The ability to manipulate images is critical when assessing pathology in complex anatomy, such as evaluation of parotid gland masses to determine deep lobe involvement, facial nerve involvement, or extension into the skull base. Images in the coronal plane are important in evaluating the submandibular gland in relation to the floor of mouth. Lymphadenopathy and its relationship to the carotid sheath and its contents and other structures are also well delineated. CT is also superior to MRI in demonstrating bone detail and calcifications. CT is also the fastest method of imaging head and neck anatomy. Other advantages of CT include widespread availability of scanners, high‐resolution images, and speed of image acquisition that reduces motion artifacts. Exposure to ionizing radiation and the administration of IV contrast are the only significant disadvantages to CT scanning.
CT Technique
The CT scanner contains a gantry, which holds an X‐ray tube and a set of detectors. The X‐ray tube is positioned opposite the detectors and is physically coupled. A “fan beam” of X‐rays are produced and pass through the patient to the detectors as the tube and detector rotate around the patient. In newer generation of scanners, the multiple rows of detectors are fixed around the gantry and only the tube rotates. A table carries the patient through the gantry. The detectors send signals, dependent on the degree of X‐ray attenuation, to a computer that uses these data to construct an image using complex algorithms.
Intravenous contrast is administered for most CT studies, especially in the head and neck. IV contrast is a solution consisting of organic compounds bonded with iodine molecules. Iodine is a dense atom with an atomic weight of 127, which is good at absorbing X‐rays, and is biocompatible. IV contrast readily attenuates the X‐ray beam at concentrations optimal for vascular and soft tissue “enhancement,” but short of causing attenuation‐related artifacts. Streak artifacts, however, can occur if the concentration is too high, as seen occasionally at the thoracic inlet and supraclavicular region from dense opacification of the subclavian vein during rapid bolus injection of IV contrast.
CT of the neck should be performed with intravenous contrast whenever possible to optimize delineation of masses, inflammatory or infectious changes in the tissues, and enhance vascular structures. Imaging is obtained from the level of the orbits through the aortic arch in the axial plane with breath hold. The images are reconstructed using a computer algorithm to optimize soft