Comparative study of MR sialography and digital subtraction sialography for benign salivary gland disorders

Abstract

Background and purpose: MR sialography has become an alternative imaging technique for ductal salivary gland diseases. We compared the diagnostic accuracies of MR sialography and digital subtraction sialography in patients with successful completion of both examinations and benign salivary gland disorders.

Methods: In a prospective study, we attempted to examine salivary glands in 80 patients with clinically suspected diagnoses of sialadenitis and/or sialolithiasis. Each patient underwent digital subtraction sialography and MR sialography. MR sialography was obtained with a T2-weighted single-shot turbo spin-echo sequence (TR/TE 2800/1100 msec, acquisition time 7 seconds), with use of a quadrature head coil. Final diagnoses were confirmed by clinical follow-up and results of biopsy (n = 9) or surgery (n = 19).

Results: Failure rate was 5% (four of 80) for MR sialography and 14% (11 of 80) for digital subtraction sialography. Eighty-one salivary glands (48 parotid, 33 submandibular) in 65 patients were successfully visualized with both modalities. MR sialography depicted the main ductal system and first- and second-order branches, whereas digital subtraction sialography was able to depict third-order branches. Sensitivity and specificity to diagnose chronic sialadenitis were 70% and 98% with MR and 96% and 100% with digital subtraction sialography. MR sialography enabled diagnosis of sialolithiasis with a sensitivity of 80% and a specificity of 98% versus 90% and 98% for each with digital subtraction sialography.

Conclusion: MR sialography with a heavily T2-weighted sequence is highly successful in the noninvasive visualization of the ductal system of major salivary glands. It is useful for diagnosing sialolithiasis and sialadenitis. Digital subtraction sialography, an invasive technique, had a substantial procedural failure rate, particularly for the submandibular duct. However, because of its higher spatial resolution, successfully completed digital subtraction sialography achieved superior diagnostic information compared with that of MR sialography.

Fig 1.

A and B, Normal heavily T2-weighted turbo spin-echo (2800/1100 ms, flip angle 150°, acquisition time 7 seconds) MR sialograms obtained before (A) and after (B) salivation stimulation in a patient with status post acute parotiditis. Stensen duct (arrowheads in B) is better delineated after stimulation of salivation with a lemon mouth swab than before salivation stimulation.

Fig 2.

59-year-old man with a history of chronic sialadenitis of the left parotid gland. A, Lateral digital subtraction sialogram shows multiple strictures, sialectasis, and prestenotic dilatation of the Stensen duct (arrows) and also of secondary and tertiary branching intraglandular ducts (arrowheads). B, Lateral MR sialogram shows the same abnormal findings but at lesser spatial resolution. Subtle strictures are more difficult to visualize and sialectasis is not as prominent (arrow). The enlargement of the ductal system is demonstrated up to secondary branching ducts.

Fig 3.

61-year-old woman with status post acute sialadenitis. A and B, Oblique sagittal-coronal MR sialogram (A) and lateral digital subtraction sialogram (B) reveal normal ductal anatomy without abnormal findings. However, due to higher spatial resolution, the digital subtraction sialogram shows better delineation of ductal morphology and enables visualization of peripheral intraglandular ductal branches. Because of its normal small size, the Stensen duct shows some focal signal voids in A (compare with the enlarged duct in Fig 2B).

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.

Fig 5.

36-year-old patient suspected to have sialolithiasis. A, Lateral digital subtraction sialogram shows a slightly dilated Wharton duct (arrow) and sialectasis in secondary duct branches (arrowhead). No filling defect in the main duct is seen. B, Transverse MR sialogram shows a filling defect near the orifice of the left Wharton duct (arrow). Note also the markedly dilated left Wharton duct compared with the right side. Patient underwent surgery, and a sialith was confirmed. The false-negative digital subtraction sialographic result may be due to dental hardware or to the fact that the sialographic catheter already passed the distal stone.

Fig 6.

55-year-old patient suspected to have an intraparenchymal cyst. A, Oblique sagittal-coronal MR sialogram shows a fluid-filled cystic mass lesion (arrows) in the lower parotid parenchyma. B, Lateral digital subtraction sialogram shows no connection between the ductal structures and the cyst. However, displacement of the lower pole ducts is depicted (arrow).