Key words
head/neck - salivary glands - ultrasound
Introduction
There are six large extraoral salivary glands including two parotid glands, two submandibular
glands, and two sublingual glands. Obstructive sialadenitis refers to inflammation
of these glands caused by an obstruction of the excretory duct. Obstructive sialadenitis
is characterized by reduced or absent saliva excretion of the affected gland with
a subsequent bacterial superinfection. Absolute saliva production is not affected.
The symptoms of obstructive sialadenitis are characterized by recurrent, periprandial
swelling of the gland which is often painful and lasts for hours to days.
The main cause in 60 – 70 % of cases is obstructive sialolithiasis which is usually
unilaterally symptomatic. The prevalence is approximately 1 %. It occurs primarily
between the ages of 40 and 60 [1]. Sialolithiasis with synchronous obstruction of two salivary glands occurs in less
than 3 % of cases and is considered an anatomical exception when the excretory duct
of the sublingual gland as a normal variation empties exclusively into the Wharton's
duct [2].
The main causes of non-stone-based obstructive diseases are stenoses or strictures
which occur synchronously with greater frequency. This can also be caused by etiologically
largely unclarified sialadenitis as primary inflammation of the duct epithelium as
well as radioiodine therapy. A mechanical obstruction, for example caused by extraductal
compression of a tumor, is also possible. In contrast, cases of non-obstructive sialadenitis,
such as juvenile sialadenitis or autoimmune sialadenitis in Sjögren's syndrome, should
be differentiated.
Method
The updated S2K guideline describes all currently relevant diagnostic and therapeutic
methods for treating obstructive sialadenitis. The guideline was created under the
auspices of the German Society of Otorhinolaryngology, Head and Neck Surgery and the
associated societies such as the German Radiological Society, the German Society of
Dental Oral and Craniomandibular Sciences, and the German Society of Otolaryngologists
and is based on the elaborated AWMF rules for guideline development [3]. The method is explicitly described in the guideline report which is published on
the AWMF homepage together with the guideline (www.awmf.org/leitlinien/detail/II/017 – 025.html).
A group of experts including 14 members who met once for consensus building and related
discussions was involved in the creation of the guideline. The contents of the currently
expired guidelines “salivary gland infection” and “sialolithiasis” and the valid guideline
“salivary glands: hyperadenosis” were included.
Imaging methods
Sonography, conventional X-ray sialography, DSA sialography, MR sialography, sialendoscopy,
and salivary gland scintigraphy are the main imaging methods. The current guideline
provides only one consensus-based recommendation regarding modality selection for
diagnosis and recommends sonography as the method of choice. The selection of further
diagnostic methods should be made individually based on the particular method limitations
and the advantages and disadvantages.
Accurate diagnosis of lithiasis in relation to number, position, size, configuration,
and possible fixation of concretions is decisive for the later selection of the suitable
treatment method. A detailed classification for concretions and stenoses of the excretory
ducts was described in 2011 by Marchal et al. [4].
Sialendoscopy
Salivary duct endoscopy mentioned here for the sake of completeness is used in otolaryngology
and provides high-resolution imaging as well as the option of simultaneous intervention
under guidance and therefore has found broad acceptance. Acute inflammation is a relative
contraindication for sialendoscopy and conventional X-ray sialography due to the increased
risk of perforation and bacterial spread. The following only discusses radiologically
relevant imaging methods.
Sonography
Sonography using a 7.5 – 13 MHz linear probe is the method of choice and provides
significant diagnostic value due to its high availability, cost efficiency, and ability
to be implemented in cases of acute inflammation. It is also suitable for follow-up. As
a result of the superficial position of salivary glands, gland architecture and duct
systems can be evaluated on B-mode images. The high spatial resolution makes it possible
to detect mineralized concretions with a diameter of greater than 1 mm as well as
post-inflammatory duct system changes that can be characterized by changes in impedance
[5]. Better differentiation of infiltrating processes and tumorous masses can be achieved
via contrast agent enhancement or tomographic imaging [6]. Sonography visualizes abscess formations as hypoechoic, intraglandular masses.
Lymph nodes can be a possible differential diagnosis in this case. Sonography makes
it possible to detect typical prestenotic duct dilation during functional provocation
tests with ascorbic acid, for example [7]. However, the deep portion of the parotid gland can only be evaluated on a limited
basis with sonography due to the greater distance from the probe. Finally, in the
case of a negative finding, sonography cannot conclusively rule out lithiasis. In
this regard, supplementary MRI or CT diagnostic methods can be used for evaluation.
MR sialography
Highly T2-weighted sequences using the gradient echo technique, single-shot technique,
or fast spin echo technique are used for MR sialography. 3 D methods are superior
for detecting stenoses and strictures [8] ([Fig. 1]). The use of intravenous or intraductal contrast agent is not necessary due to the
typically saliva-filled, prestenotically dilated duct system. However, the poststenotic
duct segments can only be insufficiently evaluated due to a lack of saliva. Even if
MR sialography is inferior to conventional X-ray sialography for the visualization
of the smallest branches of the duct system, it provides superior visualization of
the duct system in relation to periductal soft tissue structures and can be performed
in a pain-free manner ([Fig. 2]). The spatial resolution MR sialography is inferior to that of sialendoscopy and
the differentiation between concretions, mucus obstructions, and polyps is also complicated
by comparable MR signaling of different pathological processes [8]. However, artificial dilation of the duct system for example due to application
of endoscopic equipment, lavage, or contrast agent application does not occur. There
is no potentially painful external compression as in sonography.
Fig. 1 The MIP reconstruction of strong T2-weighted sequences allows illustration of the
excretory duct: 36-year-old patient with a widened tripartite parotid duct due to
distal stenosis
Fig. 2 a 60-year-old patient with obstructive sialadenitis of the right parotid gland. The
concrement can be seen in the proximal duct with its typical signal loss (*) and dilation
of the upstream duct (→), which is already visible in the native T2w sequence. b After contrast application, the typical unilateral enhancement of the inflamed glandular
parenchyma and in this case even an inflammatory infiltration of the right infratemporal
fossa and the masticatory space can be documented.
Conventional X-ray/DSA sialography
The formerly widely used conventional X-ray and DSA sialography has been increasingly
replaced by radiation-free methods such as MR sialography or sialendoscopy performed
with an interventional intention. Contrast agent is applied to the Wharton’s duct
or parotid duct in a retrograde manner with a contrast defect or contrast stoppage
indirectly indicating the presence of an obstruction. The method has high sensitivity
and allows excellent evaluation and measurement of the distal duct system which is
helpful for the estimation of the probability of success of an intraductal treatment
method (e. g. stone extraction). Salivary stones and duct stenoses can also be treated
with a success rate of 80 % as a direct part of conventional X-ray sialography or
fluoroscopy [9]. However, inflammation of the duct system cannot be detected with this method [10].
A shared disadvantage with sialendoscopy is the usually painful and time-intensive
cannulation, particularly in the case of small-lumen Wharton’s ducts, the artificial
dilation of the duct systems, and the relative contraindication for being performed
in the acute inflammation phase.
Further procedures
The indication for additional imaging methods is limited as a result of the superficial
position of large salivary glands, the ability to effectively evaluate glands and
ducts with sonography, the possibility to perform MR sialography without the use of
a contrast agent and in a pain-free manner, and the availability of sialendoscopy
with an intervention option. Any necessary visualization of filiform duct segments
can be performed via conventional X-ray sialography with acceptance of the radiation
exposure. CT or MRI imaging is used for determining infiltration depth in the case
of neoplasias. Concretions can be delimited in particular with radiation-based methods,
while MRI is the most reliable method for detecting soft tissue changes ([Fig. 3]).
The rarely indicated scintigraphy with Tc-99 pertechnetate is available as a functional
imaging method which provides very good assessability of salivary gland functioning
but has only limited morphological significance [11]. It is not used in cases of acute obstructive sialadenitis but rather in post-therapeutic
situations, for example after the treatment of obstructive sialadenitis, external
radiation, or radiotherapy [12].
Fig. 3 For detecting especially small concrements, CT imaging is superior to MR imaging.
Here a large submandibular concrement is visible.
