Patients often present with complaints that are not directly related to structures in the oral cavity, but rather to those around it. The salivary glands are examples of peri-oral structures that are sometimes at the root of a dental patient’s chief complaint. There are many disorders of the salivary glands, but the most common conditions that affect the salivary glands are obstructions of the ductal structures. This article will review obstructive conditions of the salivary glands by giving an overview of the clinical presentation, available imaging techniques including a new cutting edge technology (cone beam computed tomography sialography), and management options.
Obstructive conditions of the salivary glands have been estimated to affect approximately one percent of the general population with a peak incidence during the fourth to sixth decades of life.1 Although both minor and major salivary glands can be affected, approximately 83 percent of cases involve the parotid and submandibular glands with the submandibular glands being the most commonly affected.2 The reason for the higher prevalence of obstructions in the submandibular gland ducts is believed to be related to the long, tortuous, upward path of the major duct, and the nature and consistency of submandibular saliva. Saliva produced from the submandibular glands has a higher mucous content which makes the consistency thicker and more likely to form a mucous plug. Among the causes of salivary obstruction, mucous plugs are considered the most common of the primary causes. Other primary causes of obstruction may include sialoliths (salivary stones) within the ductal structures and strictures (ductal narrowing). Secondary causes of salivary obstruction may include any pathological condition that impinges on the ductal structures and causes them to occlude, such as tumours of the salivary glands.
A patient with salivary obstruction typically complains of recurrent swelling in the area of the involved gland, especially before meal times; thus the term “meal time swellings”. The swelling is characteristically diffuse, and fluctuates in size reaching its greatest dimension during the meal. Following the meal, the swelling then gradually decreases in size. Although obstructions can be multiple and affect more than one gland, the clinically perceptible swelling is usually seen to involve one particular gland. Pain may also accompany the swelling but this is usually mild and subsides within a few minutes to hours following the meal. A list of the signs and symptoms that increase the diagnostic likelihood of an obstructive condition of the salivary glands are presented in Table 1.
Figure 1. Example of sialectasia (arrow) of the major duct of the parotid salivary gland.
The simple explanation for the signs and symptoms of salivary gland obstruction is that during meal times, there is an increased demand for saliva and therefore, increased production. With an obstruction present, the saliva finds resistance, and cannot be expelled. Consequently, the saliva accumulates within the ducts causing them to distend (dilated salivary ducts are described as having sialectasia as in Figure 1). It is the back pressure of the rapidly produced copious saliva that causes the swelling and pain to ensue. Fortunately, the obstruction is nearly never complete, and saliva will slowly flow around the point of obstruction resulting in the relief observed shortly after the meal. If the obstruction persists and the process described earlier is repeated over a period of time, the condition becomes chronic and the distension of the duct becomes permanent. As a result, saliva stagnates in these distended regions and becomes an inviting environment for retrograde infections, which can result in acute inflammation of the gland (termed sialadenitis). Acute sialadenitis is a painful condition that requires immediate attention and prescription of an appropriate antibiotic. Chronic sialadenitis, on the other hand, is not a medical emergency but left untreated, it will eventually lead to fibrosis of the gland.
Imaging of the salivary glands is required if obstruction of the ducts is suspected for several reasons. Sialography can confirm the clinical impression, elucidate the cause of the obstruction, localize the obstruction, and demonstrate the extent of damage to the ductal structures so that an informed decision can be made about the best management option. Imaging can be performed using one of five basic techniques: plain radiography, ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI).
Sialography, which was first performed in 1902,2 is a functional imaging examination that involves the introduction of a contrast agent into the duct orifice of the parotid or submandibular glands followed by imaging of the gland in question. Traditionally sialography has been combined with conventional two-dimensional (2-D) plain radiographs; however more recently, the technique has been combined with CT and MRI. Sialography is considered the most effective method of assessing obstructive conditions of the salivary glands. Furthermore, sialography may indirectly demonstrate the presence of a tumour in the gland region if the ductal structures appear displaced. Indications and contraindications of sialography are listed in Table 2.
Most recently, in a study that took place at our institution, the coupling of sialography and cone beam CT was examined in a prospective clinical study that compared the new protocol to the existing protocol that uses 2-D plain radiographs. In a dosimetric study, we confirmed that the radiation doses delivered by both protocols are comparable provided certain exposure parameters are chosen.3 We also objectively measured the quality of the images, and found that these same exposure parameters produced images of adequate quality while balancing the radiation dose to the patient.4 Finally, we compared the diagnostic capabilities of the two techniques and found that CBCT sialography outperformed plain imaging sialography with respect to visualization of the gland parenchyma, identification of sialoliths, and differentiating normal salivary glands from those with inflammatory changes.5 One of the cases that were done as part of the study and published is presented in Figure 2.5
Figure 2A. Figure 2B. 
Figure 2C. &nbs
p; Figure 2D.
Figure 2 – Cone beam computed tomography (cbCT) sialography of the left parotid salivary gland. (a) Lateral skull plain radiograph of the gland following contrast administration. This image was made prior to the cbCT scan to in sure adequate fill of the gland with contrast material, and demonstrates sialectasia of the primary and secondary ducts but no evidence of an obstruction as a cause for the sialectasia (b) Reformatted sagittal cbCT image of the same gland demonstrating the same findings as the plain radiograph. Three dimensional cbCT images (c) in the axial plane and (d) in the coronal plane demonstrate the cause of the sialectasia; a non-calcified sialolith (arrow) immediately proximal to the orifice of the gland duct.
Management of obstructive conditions of the salivary glands depends on many factors. These may include the type of obstruction, the location of the obstruction, the changes that have occurred to the ductal structures, and the severity of the patient’s symptoms. Mucous plugs for example, are transient and require palliative management in the form of hydration and salivary stimulation. Sialoliths can be managed by a number of methods including milking the sialolith from the duct, lithotripsy, conservative endoscopic removal, surgical removal, and finally removal of the whole gland. Management of strictures involves either radiologically-guided balloon ductoplasty or removal of the involved gland. As for secondary causes of obstruction, their management lies in control of the primary cause.
In conclusion, obstructive conditions of the salivary glands are relatively common and typically present with meal time swellings which may or may not be accompanied by pain. Imaging is required if an obstruction is suspected, and a newly developed imaging methodology, cbCT sialography, offers many advantages. Management options vary and depend on many factors. OH
Dr. Fatima M. Jadu is an Oral and Maxillofacial Radiologist, Assistant Professor and Consultant at King Abdulaziz University, Faculty of Dentistry.
Dr. Ernie Lam is an Oral and Maxillofacial Radiologist, and Professor and Head of the Discipline of Oral and Maxillofacial Radiology at the University of Toronto, Faculty of Dentistry.
Oral Health welcomes this original article.
REFERENCES:
1. Ngu RK, Brown JE, Whaites EJ, Drage NA, Ng SY, Makdissi J. Salivary duct strictures: nature and incidence in benign salivary obstruction. Dentomaxillofac Radiol. 2007 Feb;36(2):63-7.
2. White SC. Cone-beam imaging in dentistry. Health Phys. 2008 Nov;95(5):628-37.
3. Jadu FM, Yaffe M, Lam EWN. A comparative study of the effective radiation dose from cone beam CT and plain radiograph sialography. Dentomaxillofac Radiol. 2010;39:257:263.
4. Jadu FM, Hill ML, Yaffe MJ, Lam EW. Optimization of exposure parameters for cone beam computed tomography sialography. Dentomaxillofac Radiol. 2011;40:362-368.
5. Jadu FM, Lam EW. A comparative study of the diagnostic capabilities of 2D plain radiography and 3D cone beam computed tomography for sialography. Dentomaxillofac Radiol. 2013;42:20110319.
