FIG 4. 64-year-old man with a large sialith in the main parotid duct.

A, Lateral digital subtraction sialogram depicts a solid calculus in the proximal portion of the Stensen duct (arrow) and a prestenotic dilatation of intraglandular ductal structures (arrowheads). However, because of the near total obstruction of the main duct, visualization of prestenotic intraglandular structures is limited.

B, MR sialogram (oblique sagittal to coronal view) compares favorably with the digital subtraction sialogram and shows a filling defect of the proximal main parotid duct (arrow) together with prestenotic dilatation of intraglandular ducts. However, because of surrounding fluid, the single calculus on the MR sialogram could be misinterpreted as two separate stones. This patient was successfully treated with extracorporal lithotripsy.