Keywords

Humans have three paired major salivary glands (parotid, submandibular, and sublingual). Each gland has an individual blood supply. The parotid glands are supplied by the branches of the superficial temporal artery, the venous blood drains to the retromandibular veins. The submandibular glands obtain the blood from the facial artery with the venous outflow to the same-name veins. The sublingual glands get their blood supply via the branches of the lingual and facial arteries, venous blood drains to the lingual veins.

High-resolution sonography with intraductal and/or intravenous contrast enhancement is increasingly used to expand the possibility of ultrasound and improve its diagnostic efficiency [1,2,3,4,5]. Additionally, CEUS quantification permits more efficient, reliable, and reproducible data.

As a rule, there is no need to use CEUS in the norm, inflammatory, or degenerative changes of salivary glands. However, this method is efficient in the differential diagnosis of tumors. Focal lesions of salivary glands exhibit different patterns of contrast enhancement, which serve as a valuable diagnostic sign.

The salivary gland CEUS implicates a single intravenous injection of 2.4–4.8 ml of SonoVue®. Normally, the filling with UCA of the normal salivary gland parenchyma is intensive, regular, and symmetric with mild wash-out (Fig. 15.1).

Fig. 15.1
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Normal submandibular salivary gland. The venous phase CEUS image. Regular enhancement of the parenchyma

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Time-intensity curve parameters of salivary gland CEUS can be used for non-invasive monitoring of treatment in chronic sialadenitis with sialolithiasis and identification of tumor vascularization [6].

Salivary gland cyst typically has specific ultrasound signs, such as anechoic uniform contents with grayscale US and avascular with Doppler imaging. A simple cyst of a salivary gland, as well as of any other location, with CEUS demonstrates a characteristic perfusion defect with no contrast enhancement in all vascular phases (Fig. 15.2).

Fig. 15.2
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A simple salivary gland cyst. (a) Grayscale US image. (b) CEUS demonstrates a perfusion defect

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CEUS is often used to assess the microvascularization of salivary gland neoplasms. The parotid gland develops 70–90% of all salivary gland tumors, 8–10% arise in the submandibular and sublingual glands, and 4.9–22% in small glands [1, 7, 8].

Benign tumors of the salivary glands are most often represented by the pleomorphic adenoma. General sonography with CDI reveals clear boundaries, some circumscribing vessels, and poor blood flow within the neoplasm. With CEUS, pleomorphic adenoma is usually hypoenhanced [9] (Fig. 15.3, Video 15.1). Although some other types of tumors like Warthin's tumor (cystadenolymphoma) may appear hyperenhanced [9].

Fig. 15.3
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Pleomorphic adenoma of the parotid gland. CEUS images. (a) Patient A. The arterial phase CEUS demonstrates hypoenhancement of the lesion. (b) Patient A. The venous phase CEUS demonstrates slow wash-out. (c) Patient B. Moderate enhancement in the venous phase. (d) Patient B. The TIC quantifies slow wash-in and wash-out of the lesion

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Perfusion quantification demonstrates hypovascularity of pleomorphic adenoma with low perfusion indices and hypervascularity of adenolymphoma. The study [10] analyzed TICs in various salivary gland tumors and reported that the mean transit time (MTT) and AUC values in benign lesions (14.6 ± 1.24 s and 400.63 ± 53.85, respectively) were lower than the same in malignant tumors. However, cystadenolymphoma exhibited a higher AUC value (515.4 ± 71.26 vs. 285.82 ± 36.44, respectively) and the maximum signal increase (22.74 ± 2.69 dB/s vs. 14.32 ± 2.66 dB/s) than pleomorphic adenoma.

The special aim of CEUS is the detection and differential diagnosis of malignant tumors. Malignancies are observed in 3.6–30% of salivary gland lesions and predominantly affect the parotid glands [1, 11]. The use of UCAs is based on the identification of enhanced vascularity and neoangiogenesis. Most salivary gland malignancies are characterized by chaotic vascular branching, irregular course and caliber of the vessels, arteriovenous shunts, the inconsistency of the vascular wall, and sometimes multiple afferent vessels [1,2,3,4, 9] (Fig. 15.4).

Fig. 15.4
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Parotid gland adenocarcinoma. CEUS image with SonoVue® demonstrates irregular hyperenhancement of the tumor in the arterial phase

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Different histological types of salivary gland neoplasms have different qualitative and quantitative characteristics of contrast enhancement. CEUS can be an independent quantitative method for the evaluation of malignant and benign tumors of the parotid gland [10]. The salivary gland’s malignancies have indistinct contours and are typically hypervascular. With a quantitative assessment, they are highly perfused [9]. TIC demonstrates the MTT for malignant neoplasms of 17.94 ± 1.62 s, which is significantly higher than in benign lesions. The AUC value for malignant tumors is also significantly higher (584.9 ± 143.0).

Contrast enhancement enables detailed imaging of the vascular tree of the salivary gland tumors, which exceeds standard Doppler modes [4, 6, 10, 12,13,14].

CEUS in salivary glands has significant prospects. Further studies and accumulation of practical experience are still necessary.