Salivary Glands

KEY POINTS

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Ultrasound is anew tool for diagnoising and managing primary sjögren’s syndrome (pSS) patients.
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Only parenchymal inhomogeneity can be regarded as having true diagnostic value for pSS disease.
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Color Doppler could be a new technique to follow pSS treated patients.

Primary Sjögren’s syndrome (SS) is a chronic autoimmune disorder characterized by lymphocytic infiltrates in the lacrimal and salivary glands. Dryness of the eyes (i.e., keratoconjunctivitis sicca) and mouth (i.e., xerostomia) are the main clinical features. Histologic analysis shows lymphocytic infiltration and destruction of the affected glands.

Primary SS refers to patients who have no other connective tissue diseases or obvious identifiable cause. It is necessary to know whether the sicca syndrome is possibly caused by diabetes mellitus, hypovolemia, sarcoidosis, infection, respiratory or renal insufficiency, smoking, or medications. Investigations may be performed to document the ocular and oral dryness. These investigations include Schirmer’s test and more invasive procedures, such as salivary flow measurement, sialochemistry, sequential salivary scintigraphy, and sialography using liposoluble or hydrosoluble contrast material.

Minor salivary gland biopsy is considered the most important objective diagnostic test to confirm salivary gland involvement. However, it remains an invasive and uncomfortable technique. This is the reason why newer methods such as ultrasound are appealing alternatives. An ultrasound assessment can evaluate the gray-scale architecture of a gland and assess the degree of vascularization, which has been shown to increase in patients with primary SS.

Salivary Gland Anatomy

Parotid Gland

The parotid gland is located in the retromandibular fossa, anterior to the ear and sternocleidomastoid muscle. Parts of the superficial lobe cover the ramus of the mandible and the posterior part of the masseter muscle. The parotid gland is the largest salivary gland, averaging 5.8 cm in the craniocaudal dimension and 3.4 cm in the ventrodorsal dimension. The average weight of a parotid is 14.28 g.

Usually, the healthy parotid gland is fatty, and it is irregular, wedge shaped, and unilobular ( Fig. 17-1 ). The parotid gland is vascularized by the transverse facial artery from the superficial temporal artery ( Fig. 17-2 ).The transverse facial artery can be seen near the temporomandibular condyle.

Submandibular Gland

The submandibular gland lies in the posterior part of the submandibular triangle. The sides of the submandibular triangle are created by the anterior and posterior bellies of the digastric muscle and the body of mandible. The submandibular glands are less fatty than the parotid glands ( Fig. 17-3 ). As a result, the submandibular glands are more homogeneous and cellular on imaging.

The arterial supply to the submandibular gland comes from the submental branch of the facial artery. The facial artery forms a groove in the deep part of the gland, and it curves up around the inferior margin of the mandible to supply the face ( Fig. 17-4 ).

Ultrasound Technique for Salivary Glands

Gray-scale images are obtained using an ultrasound machine equipped with a 10- to 12.5-Mhz linear array transducer. Each patient is scanned in the supine position with the neck hyperextended and the head turned a little to the opposite side. Both parotids are examined in axial and coronal planes in B-mode ultrasound and with color Doppler. The measurements are taken in both views. Both submandibular glands are examined in coronal planes, and the measurements are taken in this view. We use B-mode ultrasound and color Doppler for evaluating the vascularization of the submandibular glands.

Normal Ultrasound Appearance

Parotid Gland

The normal echogenicity of all major salivary glands is homogeneous. The echogenicity is increased relative to adjacent muscles. In other words, the echogenicity of salivary glands is the same as the thyroid gland. Sometimes, we encounter some lymph nodes in the parotid parenchyma. In this case, it is important to check that the hyperechoic hilum is present, and it is possible with power Doppler to visualize the central vessels in normal parotid lymph nodes.

Submandibular Gland

The submandibular gland is homogeneous and located under the mandible. It is possible to see the vascularization of the gland by the submental branch of the facial artery. An ultrasound examination shows the tortuous facial artery crossing the parenchyma (see Fig. 17-4 ). The facial nerve can be visualized behind and outside the gland.

Use of Ultrasound in Primary Sjögren’s Syndrome

Abnormalities on B-Mode Ultrasound

Ultrasound is a noninvasive and inexpensive technique. In B-mode ultrasound, the following parameters can be recorded:

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Echogenicity of the gland (compared with the thyroid gland or when the thyroid is affected by surrounding anatomic structures such as muscles or fat)
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Homogenicity of the gland (homogeneous, inhomogeneous, and heterogeneous)
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Size (less studied and methodologies vary among studies)
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Posterior glandular border (well defined to borders not visible).

Since 1988, a growing number of studies evaluating the salivary glands of primary SS patients with ultrasound have been published, and nine sets of classification criteria have been suggested and used for the diagnosis of primary SS in the past 3 decades. Most investigators reported parenchymal inhomogenicity of salivary glands with hypoechogenic areas as the most important sonographic sign in primary SS ( Figs. 17-5 and 17-6 ). In the acute stage of primary SS, the salivary glands were swollen and hypoechogenic, often with marked heterogeneity due to inflammation, node enlargement, and myoepithelial hyperplasia. Multiple cysts were found. In long-standing disease, the salivary glands were usually small, hypoechogenic, and poorly demarcated.

Several studies evaluated the capability of ultrasound to detect salivary gland abnormalities. The accuracy of ultrasound ( Table 17-1 ) varied according to the imaging technique used as comparator.

Table 17-1

Diagnostic Values of Imaging Techniques for the Salivary Glands

Imaging Method	Sensitivity (%)	Specificity (%)	Studies
Scintigraphy	73-80	Quite poor	Markusse et al, 1993
			Håkansson et al, 1994
			Saito et al, 1997
X-ray sialography	72	92	Vitali et al, 1996
	72	85	Salaffi et al, 2008
Scintigraphy	82	62	Vitali et al, 1996
	70	82	Salaffi et al, 2008
Labial biopsy	87	90	Vitali et al, 1996
	63	83	Salaffi et al, 2000
Magnetic resonance imaging	71-100	93	Niemelä et al, 2004
			Makula et al, 2000
			Vogl et al, 1996
			Valesini et al, 1994
			Späth et al, 1991
Ultrasound	58.8	98.7	Hocevar et al, 2005
	75.3	83.5	Salaffi et al, 2008
	84.4	73	Poul et al, 2008
	87.1	90.8	Milic et al, 2009