First performed in 1902, sialography is a radiographic technique where a radiopaque contrast agent is infused into the ductal system of a salivary gland before imaging with plain films/digital image receptors, fluoroscopy, panoramic radiography, CBCT imaging, or MDCT imaging. Sialography is the most detailed way to image the ductal system (Figs. 29-4 to 29-6). CBCT imaging has been developed more recently as an imaging modality for conventional sialography. Its advantages are multiplanar and three-dimensional visualization of the ductal structures and the ability to remove overlapping anatomic structures from the image for better visualization of the gland.

The ductal systems of the parotid and submandibular glands are most readily studied with this technique. Although the sublingual gland is difficult to infuse intentionally, it may be fortuitously opacified while Wharton’s duct is infused to image the submandibular gland. A survey or “scout” image is usually acquired before infusion of the contrast solution into the ductal system as an aid in verifying the optimal exposure factors and patient positioning parameters as well as detection of radiopaque sialoliths or extraglandular pathosis.

With this technique, a lacrimal or periodontal probe is used to dilate the sphincter at the ductal orifice before the passage of a cannula (blunt needle or catheter) connected by extension tubing to a syringe containing contrast agent. Lipid-soluble (e.g., Ethiodol) or non–lipid-soluble (e.g., Sinografin) contrast solution is slowly infused until the patient feels discomfort (usually between 0.2 and 1.5 mL, depending on the gland being studied). These iodine-containing agents render the ductal system radiopaque. The filling phase can be monitored by fluoroscopy or with static projection images. The intent is to opacify the ductal system proximally to the acini. The image of the ductal system appears as “tree limbs,” with no area of the gland devoid of ducts. With acinar filling, the “tree” comes into “bloom,” which is the typical appearance of the parenchymal opacification phase (see Figs. 29-4 to 29-6). The gland is allowed to empty for 5 minutes without stimulation. If postevacuation images suggest retention of contrast agent, a sialagogue, such as lemon juice or 2% citric acid, may be administered to augment evacuation by stimulating secretion. Non–lipid-soluble contrast agents are preferred because of reports of inflammatory reactions subsequent to inadvertent extravasation of lipid-soluble agents. In addition to static projection radiographic images, the opacified gland can be imaged with CBCT, MDCT, or panoramic imaging techniques. CBCT imaging and MDCT imaging have the advantage of providing three-dimensional visualization.

Sialography is indicated for the evaluation of chronic inflammatory diseases and ductal pathoses. Contraindications include acute infection, known sensitivity to iodine-containing compounds, and immediately anticipated thyroid function tests.

CBCT imaging is useful in evaluating structures in and adjacent to salivary glands but cannot resolve differences in soft tissue densities. Minimally calcified sialolithiasis is well depicted on CBCT imaging, and it is useful as a recording modality for conventional sialography, providing three-dimensional visualization of the ductal structure (Fig. 29-7).

MDCT imaging is useful in evaluating structures in and adjacent to salivary glands; it displays both soft and hard tissues and minute differences in soft tissue densities. Thin axial and coronal images with a soft tissue algorithm are commonly acquired after intravenous administration of a contrast agent (Fig. 29-8). (See Chapter 14 for a description of the MDCT imaging process.) The imaging study is typically assessed in both hard and soft tissue windows. Glandular tissues are usually easily discernible from surrounding fat and muscle. The parotid glands are more radiopaque than the surrounding fat but less opaque than adjacent muscles. Although the submandibular and sublingual glands are similar in density to adjacent muscles, they are readily identified on the basis of shape and location. The submandibular and sublingual glands are most easily identified on directly acquired contrast-enhanced coronal MDCT scans. MDCT imaging is useful in assessing acute inflammatory processes and abscesses, cysts, mucoceles, and neoplasia. Calcifications such as sialoliths are also well depicted with MDCT imaging (Fig. 29-9). However, MDCT is not recognized as a sensitive study for salivary tumors per se.

MRI typically provides a different and superior soft tissue contrast resolution than MDCT imaging; it also results in fewer problems with streak artifacts from metallic dental restorative materials (Fig. 29-10). (See Chapter 14 for a description of the basic concepts and principles of MRI.)

MRI can be an alternative to conventional sialography in evaluating ductal pathosis, especially when ductal catheterization is either problematic or contraindicated. Before imaging, the patient is given lemon juice or a similar sialagogue to stimulate salivation. The MRI study is performed using rapid acquisition with relaxation enhancement sequence and a three-dimensional constructive interference in steady state sequence. The images may be reformatted using a multiplanar reconstruction software algorithm.

Although indications for MDCT imaging and MRI occasionally overlap, MRI is usually the imaging method of choice in evaluating parenchymal masses or cystic lesions because of superior display of salivary gland masses, internal structures, and regional extension of the lesions into adjacent tissues or spaces, especially in examining the submandibular glands. The use of intravenous contrast agent (most commonly gadolinium) is helpful in distinguishing between cystic and solid masses and in evaluating perineural spread of malignant tumors. Sublingual masses should always be studied by MRI because of their high incidence of malignancy. Studies have shown MRI with evoked salivation, sometimes termed “MR sialography,” as a natural contrast medium to reveal ductal morphology accurately and to identify sialoliths. Axial views are acquired for all sequences, with coronal and sagittal views as needed. Noncontrast T1-weighted and T2-weighted sequences are obtained, followed by T1-weighted postcontrast, fat-suppressed images. Fast spin echo T2-weighted images may also require fat suppression.

Nuclear medicine, or scintigraphy, provides a functional study of the salivary glands, taking advantage of the selective concentration of specific radiopharmaceuticals in the glands. (See Chapter 14 for a description of the nuclear medicine procedures used to acquire images.) When technetium 99m (^99mTc)-pertechnetate is injected intravenously, it is concentrated in and excreted by glandular structures, including the salivary, thyroid, and mammary glands. The radionuclide appears in the ducts of the salivary glands within minutes and reaches maximal concentration within 30 to 45 minutes. A sialagogue is then administered to evaluate secretory capacity. All major salivary glands can be studied at once.

Although this technique has high diagnostic sensitivity, it lacks specificity and demonstrates minimal morphology. Pathosis may be demonstrated by an increased, decreased, or absent radionuclide uptake (Fig. 29-11). Lesions that concentrate ^99mTc-pertechnetate are Warthin’s tumors and oncocytomas. The diagnosis of salivary gland tumors from nuclear medicine scans is not completely reliable. Because of relatively low image resolution, MDCT imaging and MRI are preferred for the evaluation of salivary masses. A specialized form of nuclear medicine is positron emission tomography (PET). Despite a much greater resolution than scintigraphy, PET has not been useful for classifying salivary tumors as benign or malignant.