Submandibular Strictures
Obstructive submandibular sialadenitis is characterized by recurrent swelling during meal time, reduced or absent saliva secretion from the affected gland, without a concomitant reduction in saliva production, followed by bacterial infection. The main causes of non-stone-based obstructive diseases are stenosis or strictures. Compared with a stricture, which is a short segment of intraluminal scar, with either a complete blockage or a very narrow lumen, a stenosis is a long segment with a diffuse narrowing of the ductal lumen. In contrast to obstructive stones that usually appear as a unilateral solitary pathology, strictures might occur bilaterally or with the involvement of multiple major salivary glands. Ductal strictures and stenosis in the parotid and submandibular gland (SMG) are the main cause of swellings of an unclear origin.
There is a big difference in their documented frequency between centers, using a variety of instruments for diagnosis of strictures. Medical centers specializing in salivary gland obstructive pathology and sialendoscopy find more stricture pathology in the ductal system compared with nonspecialized facilities. Submandibular strictures are not as frequent a pathology as submandibular stones. Only 25–30% of all stenosis and stricture cases are associated with the Wharton’s duct. This is probably due to an initial larger diameter of Wharton’s duct (2–3 mm) compared with the Stensen’s duct (1.5 mm).
Etiology
The vast majority of submandibular strictures are idiopathic. One explanation is that diminished salivary flow eventually causes atrophy of the ductal system by the narrowing of the ductal diameter. Certain strictures are caused by a known etiology that is typical of the SMG: trauma to the papilla orifice or the distal part of the duct due to surgery on floor of the mouth; previous attempts of stone removal from the duct; endoscopic or transoral trauma to the papilla orifice; or because of poor fitting dentures or dental prosthesis ( Figs. 29.1–29.3 ).
Strictures can be related to the presence of stones in the ductal system. Whether the initial cause is a stricture pathology leading to salivary stasis and stone formation or whether the stone blocks the duct and leads to stenosis, is unclear.
Radioactive iodine treatment for thyroid and autoimmune diseases impacts mainly the parotid gland; however, less commonly, it also affects the SMG and duct. Radiation treatment damages the glandular function and can create a diffuse stenosis of the duct.
Imaging Modalities
Ultrasound, sialography, cone beam sialography, magnetic resonance (MR) sialography, and sialendoscopy, are the main methods used to diagnose stricture pathology of the salivary glands. Most of the submandibular duct is located in the floor of the mouth. The lower jaw interference and artifact from dental restoration must be taken into account when selecting the most suitable imaging technique.
Ultrasound is a readily available, cost-effective, and radiation free method for detecting sialadenitis. In cases of stricture, it can demonstrate the ductal dilatation proximal to the stricture. The main disadvantage of this modality for SMG stricture diagnosis is that in the cases of a negative finding, stricture involvement cannot be ruled out, particularly in the distal, anterior part of the duct.
Sialography is considered the gold standard for ductal system evaluation ( Fig. 29.4 ). Cone-beam computed tomography (CBCT) has high resolution and low radiation dose. It is widely used in the head and neck and for dento-maxillofacial diagnosis ( Fig. 29.5 ). CBCT sialography is superior to conventional sialography because of the 3D reconstructions that can be performed and viewed from any direction and at any slice thickness. The 3D reconstruction enables the location of the stricture or stenosis in the ductal system and facilitates the treatment plan. The main advantage of this technique is facilitating accurate mapping of salivary ducts. The image resolution is not altered by the presence of dental restorations, so it can demonstrate the whole duct in the floor of the mouth. Disadvantages of this technique include the necessity of ductal cannulation and contrast medium injection, which might cause ductal inflammation to the SMG.
