Usefulness of Magnetic Resonance Sialography for the Evaluation of Radioactive Iodine-Induced Sialadenitis

Purpose: Radioactive iodine (RAI) ablation therapy after thyroidectomy commonly leads to obstructive sialadenitis. Magnetic resonance (MR) sialography is an emerging imaging modality that enables morphological and functional changes to be evaluated. This study was conducted to investigate the usefulness of MR sialography for the evaluation of RAI sialadenitis. In addition, the authors evaluated the correlation of MR sialographic grading with symptom severity using a symptom questionnaire (SQ), and salivary gland (SG) functions as determined by salivary flow rates (SFRs) and salivary scintigraphy (SSG) parameters. Methods: Eighteen patients with RAI sialadenitis who underwent MR sialography imaging were retrospectively enrolled. Subjective symptom scores were assessed and objective SG functions were evaluated. MR sialographic characteristics were analyzed and correlations between MR sialographic findings and clinicopathologic data, SQ, SFRs, and SSG parameters were investigated. Results: MR sialography demonstrated diagnostic findings of ductal stenosis and sialectasis, non-visualized ducts, and glandular atrophy mainly involving parotid glands. A significant correlation was found between obstructive symptom scores and ductal stenosis and sialectasis grades (both p < 0.05). Degrees of ductal stenosis and sialectasis were significantly correlated with SSG excretory variables [time from stimulation to minimum count (t_min) and maximum secretion; all p < 0.05]. Significant linear correlations were found between duct nonvisualization and uptake variables [uptake ratio (UR) and maximum accumulation (MA); both p < 0.05]. Glandular volumes were also significantly correlated with UR and MA (both p < 0.05). Conclusions: MR sialography images are useful for evaluating RAI sialadenitis, and its findings are in accordance with disease severity. An MR sialographic grading system is suggested to describe the severity of obstructive sialadenitis and SG dysfunction.