Chapter 30 Accessory organs of the gastrointestinal tract

Salivary Glands

Plain radiography imaging alone cannot be considered an accurate imaging method as only 50% of parotid gland and 20% of submandibular gland sialoliths are radio-opaque.¹ Therefore, contrast enhancement of the ducts is required or other imaging modalities must be considered: computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI) and radionuclide imaging (RNI) all have increasing roles to play in demonstrating this area and will be discussed briefly later in this chapter. In addition to diagnosis, imaging is also a precursor to interventional techniques, such as basket removal of sialoliths.

Contrast-enhanced X-ray imaging of the salivary glands has traditionally remained relatively constant in its technique; usually only parotid and submandibular glands are imaged using contrast agents, as it is considered more difficult to cannulate the sublingual gland. Submental occlusal radiography can be used to assess the sublingual region but will only show radio-opaque calculi (see Chapter 21).

Referral criteria

• Pain

• Swelling

Both symptoms are often noted on or after eating.

Sialography

Parotid glands

Control images for sialography can be taken prior to application of the sialogue, for preassessment of any radio-opaque calculi.

Image receptor (IR) position is dictated by patient position during the procedure, as patient or investigator preferences influence whether a supine or erect sitting position is used.

Control images required:

1 Anteroposterior (AP) (fronto-occipital (FO) position) projection with the head rotated 5° away from the side under investigation. Centre midway between the symphysis menti and the angle of the mandible on the side under examination. Collimate to include soft tissues of the neck and face, symphysis menti and zygoma on the side under examination. Figure 30.1 shows an AP projection (of the right submandibular gland) after contrast injection

2 Lateral, centred to the angle of mandible. Collimate to include soft tissues of the neck and under the chin, external auditory meatus, zygoma, and to level with the ala of the nose anteriorly. Figure 30.2 shows a lateral projection (of the right parotid gland) after contrast injection

3 Lateral oblique with the patient’s head tilted 15° towards the side under investigation. Tube angle of 10–15° cranially, centre midway between the angles of mandible. Figure 30.3 shows a lateral oblique projection (of the right submandibular gland) after contrast injection

Figure 30.1 AP – submandibular gland.

Figure 30.2 Lateral – parotid gland.

From Ryan S, et al. Anatomy for diagnostic imaging. 2nd ed. Edinburgh: Saunders; 2004.

Figure 30.3 Lateral oblique – submandibular gland.

Technique

• If the gland is not visible, the sialogogue may be used to promote salivation

• Saliva is blotted away from the duct area using a gauze swab and the duct is dilated with a lacrimal dilator

• The duct is cannulated, using the blunt-ended sialographic needle/catheter apparatus

• Following cannulation, up to 2 mL of contrast are injected until the patient indicates that the gland feels ‘full’ (see the preparation section with regard to a signal for this)

• The catheter tubing is taped to the skin surface, away from the duct and gland area

• The precontrast images are repeated

• After the images have been taken the patient is given a mouthwash to promote saliva secretion and a lateral view can then be taken to demonstrate drainage of the duct and any sialectasis if present

Submandibular gland

Control images required:

1 A lower occlusal image, with the IR possibly displaced over to the side in question

2 Lateral, as for the parotid gland, centred to the angle of mandible with the floor of the mouth depressed by a wooden spatula

3 Lateral oblique, as for the parotid gland

Technique

• The procedure then follows that described for the parotid gland, but the occlusal film is not required after contrast introduction and it is not necessary to use a spatula in the lateral projection. A post-sialogogue lateral film is required

Aftercare: parotid and submandibular glands

• Provide further mouthwash, if the patient requires it

• Advise the patient that they may experience an unusual taste (which may occur intermittently) until the contrast has fully drained

Possible complications: parotid and submandibular glands

• Infection

• Duct orifice damage

• Duct rupture

Other imaging techniques for the salivary glands

Digital subtraction sialography

On the whole this technique is as described for traditional sialography with contrast agent but using digital subtraction. It is similar in its imaging process to arterial radiography by the fact that an increased frame rate (usually approx. 2 frames per second) is used and the resultant image is subtracted; therefore, only the contrast-enhanced area is visualised. This method has been shown to be of high quality compared to CT, MRI and US, particularly in demonstrating pathology in the parenchymal part of the gland.⁴ There is, however, an increase in patient radiation dose compared to conventional technique, therefore the benefit of image quality versus radiation dose should be considered when using this technique.

Magnetic resonance sialography

This is a non-invasive technique and, with advances in equipment and availability, is becoming more popular. Indeed, it has been stated that it is now ‘routinely’ used to image the salivary parenchyma but that contrast X-ray is still mainly used to show the ducts.⁵ It has long been compared favourably to conventional techniques.⁶ Its obvious advantage is that it uses hydrographic technique (relying on the presence of the patient’s own saliva), so no cannulation is required, and of course there is no ionising radiation. However, to combat the spatial resolution difference a number of methods have been used: these include the use of a sialogogue for dynamic studies and also the use of small surface coils.^7,⁸ A recent study showed that using a sialogogue and a passive occlusion device (a pad used to compress and occlude the opening of the duct) is comparable with interventional methods, particularly when assessing the parotid gland;⁵ however it must be noted that the investigators had undertaken research on volunteers, recognising that further study on patients was required in order to assess diagnostic performance and the practicality of this technique.

CT

With duct cannulation and contrast enhancement, CT is also being used more frequently. It is considered to be most useful in imaging (without contrast) for tumour enhancement or in patients who have a mass lesion. Radiation dose plays an important factor, especially compared to all other techniques, but image quality is high.

Ultrasound

This has an increasing role in assessing the salivary glands, particularly when using Doppler. All major pathologies exhibit classic signs of hypoechoic, anechoic or inhomogeneous areas that can be recognised and aid in differential diagnosis.⁹ Owing to its non-invasive nature and capability in detecting numerous pathologies, ultrasound can be extremely useful as a front-line investigation but it is known to be difficult to detect sialoliths with ultrasound, or in chronic cases where the gland does not function.⁹

It is particularly useful for assessing solid mass salivary gland pathology, and also effective in conjunction with fine needle aspiration because of the high resolution that can be attained. It has also been advocated as a quick and simple process to use in assisting fine needle aspiration of tumours.⁶

RNI

Particularly useful as a safe and reliable method to assess gland function. It is also proving to be reliable in the differential diagnosis of patients with suspected Sjögren’s syndrome.¹⁰

Gallbladder and Biliary Tree

Oral cholecystography

Oral cholecystography remains an excellent method of gallstone detection but its role has diminished, mainly due to the advantages of alternative imaging methods (especially ultrasound ¹¹). It is rarely carried out in the UK but is still considered to be an option in some imaging departments.

The examination has three phases:

1 Control plain radiography

2 Contrast images

3 Gallbladder showing drainage of contrast after fatty meal (AFM)

Referral criteria

• Suspected gallbladder pathology

Contraindications

• Hepatorenal disease

• Serum bilirubin levels in excess of 34 µmol/L

• Acute cholecystitis

• Dehydration

• Previous cholecystectomy

Contrast agent

• There are a number of agents on the market, all producing the required result. The most common are sodium iopodate (Biloptin) and iopanoic acid (Telepaque)

First stage of the examination and patient preparation

• Prior to the examination a control image is taken. Its use was advocated by Twomey et al.,¹² who estimated that it could aid in the diagnosis of up to 5% of calculi. The projection used for this is the 20° left anterior oblique (LAO) described in the second-stage examination procedure and positioning technique