Disease Entities Affecting Salivary Glands

There are a number of disease entities that can affect the salivary glands: these entities include obstructive, inflammatory,

Disease Entities Affecting Salivary Glands
autoimmune, and neoplastic processes. In addition, swellings or enlargements in the region of the major salivary glands can arise in structures outside the glands, including lymph nodes, cysts, nonsalivary neoplasms, and muscle hypertrophy. Imaging may be of value in differentiating between various diseases and in staging the degree of tissue destruction.
Plain films are frequently helpful when an obstructive disease is suspected, although about 20% of the sialoliths in the submandibular gland and 40% of the sialoliths in the parotid gland are not well calcified and will thus appear radiolucent on radiographs.Occlusal radiography can be used to demonstrate submandibular sialoliths, with a standard topographic or cross-sectional view and with the beam entering under the chin and striking the film at 90˚ (Figure 3-17). In the posterior

Disease Entities Affecting Salivary Glands
region, a more oblique angle may be needed to visualize the stone, projecting it forward onto the film. In general, a reduced exposure time is needed because the stone is less calcified than bone or teeth. Periapical radiography in the buccal vestibule may demonstrate a sialolith in the parotid duct. Various extraoral views may also be needed to visualize a stone, depending on its location.
Sialography, in which a radiopaque contrast medium is instilled into the duct of a salivary gland prior to imaging, permits a thorough evaluation of the ductal system of the major glands. It can demonstrate the branching pattern as well as the number and size of the ducts. Radiolucent sialoliths that are not visible on plain films can be seen as voids in the contrast medium. Sialography is indicated primarily for the evaluation of chronic inflammatory diseases and ductal pathosis, but other imaging techniques are preferred for the investigation of space-occupying masses.
Tumors in the salivary glands or surrounding areas may be investigated by a variety of techniques, including CT, MRI, and US. The selection of specific examinations should be made in consultation with a radiologist. In many institutions, CT is the procedure of choice for evaluating the salivary glands and particularly the extent of a mass since glandular tissue usually can be readily distinguished from surrounding fat and muscle. MRI, however, may better delineate the internal structure of the tumor and demonstrate extension into adjacent tissues. Ultrasonography has typically been used to differentiate solid lesions from cystic lesions in the salivary glands, but recent studies have begun to look more closely at the ultrasonographic features of various salivary tumors in an effort to aid the differential diagnosis by using a noninvasive and relatively inexpensive technique.For many years, sialography has been considered the “gold standard” for evaluating the salivary component of autoimmune diseases such as Sjögren’s syndrome. The presence of

punctate (< 1 mm) or globular (1 to 2 mm) collections of contrast medium (sialectasis) may be seen throughout the glands, progressing over time into larger pools of extraductal contrast material that may signal more advanced gland destruction.
Recently, there has been increased interest in the use of US to examine the glands in patients with Sjögren’s syndrome, primarily in respect to the degree of homogeneity of the parenchyma.While its diagnostic accuracy is not as high as that of sialography, particularly in the early stages of the disease, US may be useful in those cases in which sialography cannot be done. It has also been suggested that US could be done first, followed by sialography only in those cases that yield abnormal or equivocal ultrasonographic results.
Scintigraphy with Tc 99m pertechnetate can be used to evaluate the function of all of the salivary glands simultaneously. However, there is disagreement over how useful this technique is in determining the cause of xerostomic states. One recent study concluded that scintigraphy was not useful in determining which patients would respond to pilocarpine after radiotherapy-induced salivary dysfunction.