Sonography of the salivary glands
Due to their superficial position, the parotid, the submandibular, and the sublingual glands can be imaged with high-resolution transducers. In acute inflammatory diseases sonography can differentiate between obstructive or non-obstructive sialoadenitis. Abscess formations may be detected and the maturation of the colliquation may be controlled. Abscesses may be punctured under US guidance. In Sjögren's syndrome the sonographic changes correlate with the histological destruction, and in acute forms hypervascularization is found in color Doppler. In fibrotic cases the stimulation-induced hyperemia is impaired. In sialoadenosis inflammatory and tumorous lesions can be ruled out by sonography. Tumors of the salivary glands can be visualized with high sensitivity. Like other imaging methods the specificity in assessment of the histology of a tumor is low. Multilocular lesions, such as sarcoidosis, lymphoma, metastases, or cystadenolymphoma, are discussed. In deep located, malignant tumors or when the tumor cannot be delineated completely, MR or CT are obligatory to delineate the tumor. Sonography enables the diagnosis of cysts or ranulae. The accuracy of sonography in assessment of sialolithiasis is approximately 90%. Non-opaque stones can be visualized, too; however, small stones of less than 2 mm are difficult to detect since the posterior shadow may be missing. The concrements can be differentiated into intraductal or intraglandular stones. Indirect signs, such as ductal dilatations or inflammatory changes, may be found. Pseudotumorous lesions, such as hypertrophy of the masseter muscle, tuberculosis, sarcoidosis, or lymphoepithelial lesions in AIDS, are discussed. In children the main differential diagnosis of salivary gland pathologies are addressed. In many diseases sonography is the first-line imaging modality in assessment of salivary glands.
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