Ultrasound in the diagnosis of parotid duct obstruction not caused by sialolithiasis: diagnostic value in reference to direct visualization with sialendoscopy

OBJECTIVES: The aim of this study was to evaluate the diagnostic value of ultrasound in the obstructive pathology of the parotic gland not caused by sialolithiasis using sialendoscopy as reference standard.

METHODS: Retrospective analysis of all patients who presented with suspected diagnosis of obstructive ductal pathology of the parotid gland other than sialolithiasis between January 2011 and December 2017. 538 patients, for a total of 691 parotid glands were included in the study. Ultrasound was performed, followed by sialendoscopy in all cases. Duct diameter and parenchyma echogenicity were assessed. Direct sialendoscopic examination of the parotid duct was regarded as the reference standard.

RESULTS: Parotid glands with normal sialendoscopic findings (21.6%, n = 149) had a duct diameter of 0.3 mm (0-2.7 mm) and homogeneous hyperechoic parenchyma on ultrasound in 98.7%. Ductal inflammation/sialodochitis (32.9%, n = 227) on sialendoscopy had significantly larger ductal diameter of 0.7 mm (0-4.3 mm, p = 0.001) and hypoechoic parenchyma in 78.0% ( p < 0.001). Parotid glands with stenosis (45.6%, n = 315) had hypoechoic parenchyma in 52.6% and a ductal diameter of 4.1 mm (0-19.0 mm; p = 0.001). The ductal diameter was ≥2.7 mm in 95.6% of the stenosis (AUC 0.886, p = 0.001). Using 5.1 mm as benchmark ductal diameter, stenosis with ductal anomaly (68/315) were identifiable with a sensitivity of 92.6% and a specificity of 96.8% (AUC 0.986, p = 0.001).

CONCLUSION: Ultrasound parameters can be used to distinguish different types of obstructive ductal pathology of the parotid gland, supporting the use of this imaging modality as diagnostic tool of first choice.