Investigation of salivary gland disease

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CHAPTER 6 Investigation of salivary gland disease

Vivian E. Rushton

Contents

Introduction
Sialography

image Indications/contraindications
Complementary and competing investigations

image Ultrasonography
image Computed tomography (CT)
image Magnetic resonance (MR)
image Radioisotope imaging (sialoscintigraphy)
image Conclusion
Preoperative assessment of the patient and room preparation
Plain intraoral films for identifying calcified sialoliths
The basic equipment to perform sialography
The standard procedure
Variation of the standard technique

image Hydrostatic sialography
image Subtraction radiography
image Basket retrieval of mobile calculi
image Balloon dilatation of strictures
Aftercare
Image interpretation

image Obstructive sialadenitis
image Autoimmune sialadenitis
image Trauma and post-trauma evaluation
image Presence of tumor
References
Further reading

Introduction

Salivary gland tissue has been shown to display a wide diversity of pathology encompassing inflammatory, obstructive, infectious, neoplastic and systemic disease. Inflammatory and obstructive disease within salivary gland tissue accounts for the majority of patients seeking treatment for their symptoms whereas the incidence of salivary gland tumors is extremely low.

This pathology division is reflected in the radiological techniques employed when imaging patients with salivary gland disease. For those patients presenting with inflammatory disease, plain film radiography, either alone or in combination with contrast studies and/or ultrasonography, often comprises ‘first-line’ imaging. These techniques provide the high resolution images with which to detail the presence of salivary calculi and allow the clinician to document accurately any significant changes within the ductal architecture of the gland. For those patients in whom a mass lesion is suspected then computed tomography (CT) and magnetic resonance imaging (MRI) are the imaging modalities of choice.

The presenting symptoms of the patient are often very useful in determining the type of abnormality present. Typical symptoms of inflammatory disease are swelling of the salivary gland allied with mealtimes and the sight and smell of food followed by a gradual reduction of the swelling having eaten. The latter is highly suggestive of either obstruction by a calculus or an inflammatory induced ductal stricture which indirectly compromises salivary flow. In some cases, the patient may additionally complain of pain, a bad taste and pus may or may not be evident at the duct orifice. These symptoms and signs are indicative of current inflammatory disease. Finally, a number of patients may present with a dry mouth, the causes of which are wide ranging.

The aim of this chapter is to provide details of the most common radiographic techniques with which to image salivary gland pathology, whilst also providing the reader with an overview of each of the other competing investigations and the rationale for their use.

Sialography

The technique employs the use of contrast media to delineate the fine anatomy of the salivary gland ductal system. Patient symptoms will range from pain, which may be acute or chronic in its presentation, to a generalized recurrent or discrete swelling which is often present at mealtimes. Some patients are referred with a dry mouth which relates to a myriad of clinical conditions including autoimmune diseases, drug therapy and previous radiotherapy.

Indications

• Possible obstruction within the salivary duct system. Sialography should only be carried out after a plain radiographic examination to exclude or confirm the presence of either calcified or non-calcified sialoliths (i.e. calculi) or the presence of foreign bodies
• An evaluation of the extent of irreversible ductal damage
• To enable the differentiation between a variety of disease entities, i.e. chronic sialadenitis, Sjögren’s disease, sialosis etc
• An evaluation of fistulae, ductal trauma and ductal strictures

Contraindications

• A calculus close to the duct orifice
• Sialography should not be performed if the salivary gland is infected
• Sialography is best avoided in cases of known iodine hypersensitivity

The presence of an acute inflammatory episode would be confirmed clinically by the presence of pain and swelling of the salivary gland. Similarly, a chronically inflected salivary gland with pus emanating from the salivary duct orifice would also contraindicate sialography until the infection had been controlled by appropriate antibiotic therapy.

Complementary and competing investigations

Ultrasonography

Newer ultrasound equipment exhibits high spatial resolution. This factor, combined with the relative superficial anatomical position of the salivary gland tissue relative to the ultrasound probe, allows the operator to obtain high definition images. Similarly, the superficial topography of the salivary gland tissue also permits fine-needle aspiration biopsy and core biopsy techniques to be performed with relative ease for both the patient and the operator (Bialek et al., 2006).

The technique has become commonplace in clinical practice when assessing generalized swellings or the presence of a mass within the salivary glands.

Advantages of the technique

• Non-invasive
• Does not involve the use of ionizing radiation
• Can differentiate between intra- and extra-glandular lesions
• Use of color Doppler enables identification of vessels
• More sensitive than CT in identifying small lesions
• Can identify calculi >2 mm
• Enables fine-needle aspiration biopsy of lesions to be undertaken (Bradley, 1993)

Disadvantages of the technique

• Difficulties encountered in identifying lesions confined primarily to the deep lobe of the parotid gland
• Margins of deep lobe lesions may be difficult to identify in their entirety. Needs additional investigation using CT and/or MRI to evaluate fully the extent of the lesion

Computed tomography (CT)

The technique can be used to diagnose swellings both associated with the salivary glands themselves and those structures extrinsic to the glands.

Advantages of the technique

• Allows three-dimensional imaging
• Allows the identification of calcified sialoliths
• Enables the clinician to determine the extent of the disease
• Allows differentiation between cellulitis and abscess formation
• Allows differentiation between pathology in particular compartments in the suprahyoid neck, i.e. between the parotid and masticator space
• Determines the nature of the margins and the content of the lesion
• Determines whether the lesion is intra- or extra-capsular
• Has high sensitivity for the detection of salivary gland tumors
• CT sialography allows better delineation of the major duct architecture
• IV contrast highlights pathology

Disadvantages of the technique

• Fine anatomy of intra-glandular ducts is not well imaged
• Provides no information on salivary gland function
• Stenson’s duct seen only if markedly dilated
• Facial nerve normally not seen
• High dose to the patient
• Difficulties in differentiating benign salivary gland lesions from low-grade malignancies as both exhibit smooth margins
• Streak artefacts from adjacent metal dental restorations. However, these can be reduced by using an increased angled coronal scan geometry

Magnetic resonance (MR)

Advantages of the technique

• No use of ionizing radiation
• Major vessels identified by flow voids
• Facial nerve and ductal architecture can be identified on certain sequences
• T1 and T2 images allow differentiation between normal and abnormal salivary gland tissue
• Allows differentiation between malignant and benign lesions as margins more sharply resolved by MR
• Use of a variety of imaging sequences allows the clinician to optimize the diagnosis without the routine use of contrast agents
• MR sialography allows an assessment of the ductal architecture without the use of contrast
• Dynamic contrast enhancement studies have been shown to differentiate between different pathological lesions whilst also allowing glandular functional activity to be derived (Roberts et al., 2008)

Disadvantages of the technique

• Often difficult to distinguish a solid mass from a cyst unless there are contrast-enhanced images
• Calcifications better seen on CT
• Focal bone erosion cannot be assessed

Radioisotope imaging (sialoscintigraphy)

Advantages of the technique

• Allows an evaluation of both parenchymal function and the rate of excretion of saliva from each of the salivary glands simultaneously
• Allows the clinician to assess salivary gland tumors that can highly concentrate 99mTc pertechnetate, i.e. Warthin’s tumor and oncocytoma
• Allows analysis of the results using time-activity curves and quantitative parameters such as percentage secretion to be derived
• Employed in those rare cases where aplasia of one or more major salivary glands is suspected

Disadvantages of the technique

• High dose to the patient
• Provides no information on ductal architecture or gland anatomy
• No information available on the pathology within the salivary gland tissue
• When used, it is arguable whether there is any impact on patient management

Conclusion

There are many imaging modalities available to the clinician and the decision to choose a particular examination will be decided following a thorough clinical history and examination of the patient.

Preoperative assessment of the patient and room preparation

The type of room used will be dependent on where the examination is performed. Sialography may well be performed in the dental chair in some institutions while, in others, a dedicated angiography room (Figure 6.1) may be used to conduct the examination.

image

Figure 6.1 Room layout for sialography.

Patient identification is confirmed by the operator and a brief clinical and medical history is taken to confirm the clinical signs and symptoms and also to allow justification of the radiographic examination.

If the patient’s clinical history is suggestive of current infection within the salivary gland under consideration, then a thorough clinical examination should be conducted to verify the diagnosis. Both current infection and a prior history of an allergy to iodine would contraindicate sialography. If the presence of a calcified sialolith (a salivary stone) is suspected from the patient’s history, then either ultrasonography or plain films should be undertaken to ascertain this prior to sialography.

Plain intraoral films for identifying calcified sialoliths

For the submandibular salivary gland:

1. To assess the distal aspects of the submandibular duct: an anterior lower true occlusal (with soft tissue exposure) (Rushton, 2005)
2. To assess the proximal aspects of the submandibular duct: (a) the lower posterior oblique occlusal (with soft tissue exposure) (Rushton, 2005) or (b) a true lateral view: the patient’s index finger is used to depress the floor of the mouth so that the displaced calculus is visualized below the inferior cortex of the mandible.

An alternative method to the lower posterior oblique occlusal has been devised by Semple and Gibb (1982) for those patients who have a shortneck or limited neck movement. For those patients who cannot tolerate intraoral placement of dental films, a sectional panoramic radiograph related to the side under consideration or an extra-orally positioned occlusal film can be used (Harkin, 1983).

For the parotid salivary gland:

1. An intraoral (size 2: 31 × 41 mm) dental film placed in the buccal sulcus overlying the parotid orifice and supported by the finger of the patient.
2. An anteroposterior radiograph of the face with the patient inflating the cheek in order to detect calcified sialoliths within Stenson’s duct or the gland itself.

While additional lateral views may be employed, the presence of a calculus can be obscured by the density of bone and tooth tissue inherent within the image.

The basic equipment to perform sialography

The basic equipment to perform sialography is as follows:

• Sialographic cannulas: Rabinov-type catheters are produced by several companies with graded sizes ranging from 0.012 to 0.032 inch (0.03–0.08 cm). The largest size (0.032) cannula (Figure 6.2) has a rounded tapered closed end with bilateral side ports and is usually used for parotid sialography. The remaining cannulas are straight with an open end and are used for both submandibular sialography and for the narrow parotid orifice.
• In those cases in which a fistula has formed, either from trauma or the result of long-term infection, a higher caliber catheter (4 French) can be employed to perform a successful sialogram without reflux of contrast.
image

Figure 6.2 0.032 Rabinov catheter.

The remaining equipment (Figures 6.3 and 6.4) comprises:

• A 5 ml syringe
• Gauze pads
• A flexible high intensity light
• ×4 magnifying loupes
• Water-soluble contrast agent (typically Omnipaque 300 or equivalent)
• Micropore© tape
• Citric acid solution (or lemon juice) to act as a sialogogue.
image

Figure 6.3 Basic equipment for sialography.

image

Figure 6.4 Magnifying loupes.

(Courtesy of Lactona Corp.)

The standard procedure

• The patient is positioned supine on the table
• The orifice of the salivary gland under consideration is identified using a high intensity light. A combination of drying of the mucosa adjacent to the duct orifice, massaging the gland, the use of a sialogogue and/or the use of magnification often helps to identify the duct orifice
• If needed, the orifice can be enlarged using lacrimal dilators, although the Rabinov catheter itself is a more effective tool for this purpose
• The appropriate sized Rabinov catheter is attached to a 5 ml syringe, previously filled with water-soluble contrast media ensuring that there are no air bubbles within the solution. The latter can give a false-positive diagnosis for mucous plugs if inadvertently injected into the gland
• Following placement of the catheter, the orifice of the duct usually forms a tight seal around its circumference
• The patient is asked gently to support the plastic tube between their anterior teeth and also by pursing their lips around it.
• The tubing is stabilized using a Micropore© non-allergenic adhesive strip taped onto the patient’s forehead. The latter also ensures that the operator’s hands are not within the primary beam
• The x-ray tube is appropriately positioned relative to the salivary gland under investigation

For the parotid gland: 0.5–1.0 ml of contrast medium is injected slowly. Subsequent films would include an oblique lateral radiograph to ensure adequate filling with contrast and a PA view centered on the gland under investigation. Finally, an evacuation film should be performed after removing the catheter. If any contrast is still retained within the gland then a sialogogue should be administered.

For the submandibular gland: 0.2–0.5 ml of contrast medium is injected slowly. Films would include an oblique lateral, a true lateral and a mandibular true occlusal. Finally, an evacuation film should be performed after removing the catheter, followed by a sialogogue if contrast is still retained within the gland.

Variation of the standard technique

Hydrostatic sialography

The technique was developed to overcome the under or overfilling of salivary glands when injecting contrast using hand pressure and without the obvious benefit of monitoring the flow of contrast into the gland radiographically. The technique relies upon the positive pressure from a reservoir of contrast positioned 70–90 cm above the orifice of the salivary gland to overcome the natural pressure of the gland itself. Refinements of the technique have included the use of a constant infusion pump supplying contrast at a rate of between 0.01 and 1.0 ml/min with a transducer to record pressure.

Subtraction radiography

Post processing subtraction of bony structures provides the clinician with high definition sialographic images with which to evaluate the salivary gland ductal system. The equipment used is commonplace in digital imaging suites consisting of a C-arm, a 17 cm (smallest film/largest magnification) field image intensifier and a 512 × 512 matrix. The exposure sequence used is identical for both the parotid and the submandibular glands. It consists of one frame per second on a subtracted run followed by single acquired images. The contrast is hand injected allowing the operator to control visibly the volume of contrast entering the gland preventing overfilling.

For the parotid gland, the standard views are: a true lateral and an anteroposterior view followed by an emptying view post catheter removal. If emptying is delayed, then a sialogogue is given and a further lateral view is obtained. For the submandibular gland, the true lateral is the view of choice both for contrast filling of the gland, the emptying film and after the sialogogue has been administered (Ilgit et al., 1992; Buckenham et al., 1994).

Advantages of the technique:

• Subtraction of bony and air containing overlapping structures enables evaluation of the gland with superior quality images
• Contrast resolution is higher
• Post processing facilities enhance the image
• Demonstration of gland architecture requires less contrast and a reduced likelihood of extravasation
• Reduced exposure and shorter exposure times

Basket retrieval of mobile calculi

Basket retrieval techniques can be effectively employed for smaller mobile calculi or for calculus fragments in the middle and proximal thirds of the submandibular duct and in any region of the parotid main duct using fluoroscopic control.

Balloon dilatation of strictures

This technique employs the use of a 1.8F angioplasty balloon catheter to by-pass the stricture using digital subtraction radiography (Figure 6.5).

image

Figure 6.5 Balloon dilatation of a stricture.

Aftercare

There are no special requirements for after-care post sialography.

Image interpretation

Before commencing sialography, the pattern of the normal anatomy of the parotid gland (Figure 6.6) and the submandibular gland (Figure 6.7) should be thoroughly understood.

image

Figure 6.6 Normal anatomy of the parotid gland.

image

Figure 6.7 Normal anatomy of the submandibular gland.

The clinical presentation of patients requiring sialography can be summarized as follows:

• Obstructive sialadenitis
• Autoimmune sialadenitis
• Trauma and post-trauma evaluation
• Presence of tumor.

Obstructive sialadenitis

Obstructive sialadenitis is the result of recurrent infection within the salivary gland which usually results in a combination of both ductal strictures and dilation. The sialographic examination displays the extent of ductal damage within the gland due to these repeated inflammatory episodes. For those patients with grossly distorted ducts (Figure 6.8), gland removal is often the treatment of choice. Conversely, those patients with a localized focal stricture might well benefit from balloon dilatation. In addition, the status of the salivary gland ductal system in which a stone has recently been passed can also be assessed.

image

Figure 6.8 Obstructive chronic sialandenitis.

The sialographic findings of obstructive sialadenitis are:

• Minimal to grossly deformed ductal system
• Areas of focal strictures and dilation of the main duct, the so-called ’string of sausages’ appearance (Figure 6.9)
• Involvement of the secondary duct system.
image

Figure 6.9 Focal strictures and dilation of the main duct appearing as the so-called ‘string of sausages’.

Autoimmune sialadenitis

The majority of patients presenting with this condition will be suffering from Sjögren’s syndrome (Roberts et al., 2008). The patients present with salivary gland enlargement and classification of the sialographic findings relate primarily to the size of the dilated secondary ducts. Punctate sialectasis is used to describe cases with dilation less than 1 mm in diameter, globular sialectasis for those between 1 and 2 mm and for those cases with non-uniform duct diameter greater than 2 mm, the term cavitatory sialectasis is used (Figure 6.10).

image

Figure 6.10 Cavitatory sialectasis evident in this patient with Sjögren’s syndrome.

Trauma and post-trauma evaluation

Sialography can be extremely useful in identifying the site and extent of duct and/or glandular trauma. Common findings are the presence of a fistula (Figure 6.11) or complete occlusion of the duct.

image

Figure 6.11 Laceration of the main duct of the parotid gland. The use of a larger cannula allowed an assessment of the detriment to the main duct and the gland itself. Contrast can be seen extravasating into soft tissue

Presence of tumor

Sialography can often highlight the presence of a salivary gland mass, although MR and CT would be the imaging modality of choice if a mass lesion was suspected. The sialographic signs of a mass lesion are:

• ‘Ball in hand’ appearance due to ductal splaying around an expanding mass lesion (Figure 6.12)
• Ductal cut off caused by a mass compressing and occluding the duct
• Ductal irregularities due to the presence of an infiltrating lesion and contrast pooling within the gland.
image

Figure 6.12 The ducts associated with the inferior aspects of the parotid gland display a ‘ball in hand’ appearance due to ductal splaying around an expanding mass.

References

Bialek E.J., Jakubowski W., Zajkowski P., et al. US of the major salivary glands: anatomy and spatial relationships, pathological conditions and pitfalls. Radiographics. 2006;26:745-763.

Bradley M.J. Ultrasonography in the investigation of salivary gland disease. Dentomaxillofac. Radiol.. 1993;22:115-119.

Buckenham T.M., George C.D., McVicar D., Moody A.R., Coles G.S. Digital sialography: imaging and intervention. Br. J. Radiol.. 1994;67:524-529.

Harkin P. Demonstration of submandibular calculi. Radiography. 1983;49:84.

Ilgit E.T., Cizmeli O., Isit S., et al. Digital subtraction sialography: technique, advantages and results in 107 cases. Eur. J. Radiol.. 1992;15:244-247.

Roberts C., Parker G.J.M., et al. Glandular function in Sjögren’s syndrome: assessment with dynamic contrast enhanced MR imaging and tracer kinetic modelling-initial experience. Radiology. 2008;246:845-853.

Rushton V.E. Section 10: dental radiography. In Whitely A.S., editor: Clark’s positioning in radiography, twelth ed., Hodder Arnold Publication, 2005.

Semple J., Gibb D. The posterior-anterior lower occlusal view – a routine projection for the submandibular gland. Radiography. 1982;48:122-124.

Further reading

Blair G.S. Hydrostatic sialography: an analysis of the technique. Oral Surg.. 1973;36:116-130.

Buckenham T.M., Page J.E., Jeddy T. Technical report: interventional sialography – balloon dilatation of a Stenson’s duct stricture using digital subtraction sialography. Clin. Radiol.. 1992;45:34.

Luyk N.H., Doyle T., Fergusson M.M. Recent trends in imaging the salivary glands. Dentomaxillofac. Radiol.. 1991;20:3-10.

McGurk M., Escudier M.P., Brown J.E. Modern management of salivary calculi. Br. J. Oral. Surg.. 2005;92:107-112.

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Murray M.E., Buckenham T.M., Joseph A.E.A. The role of ultrasound in screening patients referred for sialography: a possible protocol. Clin. Otolaryngol. 1996;21:21-23.

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