Diagnostic accuracy of ultrasound and MRI in parotid gland tumors: A retrospective study

Abstract

Parotid gland tumors (PGTs) are the most common salivary gland neoplasms, encompassing diverse benign and malignant pathologies. Accurate preoperative diagnosis is vital for surgical planning, functional outcomes (e.g., facial nerve preservation), and prognosis. While histopathology remains the gold standard, non-invasive imaging, such as ultrasound (US) and MRI, plays a critical role in initial tumor characterization. US is widely used due to its accessibility and cost-effectiveness, but its utility is constrained by acoustic limitations and operator dependence. MRI, with superior soft tissue contrast and multiplanar capabilities, excels in delineating tumor extent and neural involvement but often struggles to differentiate benign from malignant lesions due to overlapping imaging features. The comparisons of diagnostic performance between US and MRI limited, and optimal imaging parameters for specific PGT subtypes remain underinvestigated. The aim of the present study was to review and summarize the clinical presentations and histological types of parotid tumors, whilst also evaluating the diagnostic accuracy of US and MRI, to determine optimal US imaging parameters for pleomorphic adenomas and Warthin tumors. The medical records, including imaging examination results, type of parotidectomy and postoperative pathological findings, of 214 patients with confirmed PGTs were collected from the database of Central Hospital of Wuhan (Wuhan, China). The nature of the tumor was assessed based on imaging findings (US and MRI), with postoperative pathology (hematoxylin and eosin and immunohistochemistry) used as the gold standard. The sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) for US and MRI were established. The area under the curve (AUC) was computed to compare the accuracy of US and MRI in identifying the nature of parotid gland tumors. The Youden index was calculated to evaluate the diagnostic power. Data analysis was conducted using SPSS version 29.0, where statistical significance was set at P<0.05 using the χ² test. In the field of PGT diagnosis, the combination of US and MRI technologies was found to significantly enhance diagnostic precision. This integrated approach showed a statistically significant improvement over the use of US alone (P<0.05). Although MRI, as an independent modality, showed higher accuracy compared with that of US, the difference between MRI and US was not statistically significant. The receiver operating characteristic curve analysis indicated that the AUC for MRI in diagnosing benign and malignant parotid gland tumors was 0.899, which was significantly greater compared with that of US (0.702; P<0.001). The combined diagnosis using US and MRI achieved the highest specificity (94.8%), compared with US (52.6%) and MRI (71.9%) alone. For the combined US-MRI approach, the PPV, NPV and Youden index were 84.6, 95.0 and 0.68%. For US and MRI alone, the PPV, NPV and Youden index were 64.7, 94.1 and 0.34%, and 75.8, 95.0 and 0.67%, respectively. To conclude, these data suggest that the amalgamation of MRI and US can provide an efficacious means of diagnosing PGTs, thereby constituting an instrumentation for the preoperative qualitative evaluation of these tumors.

Keywords: MRI; parotid gland tumor; parotidectomy; ultrasound.

Figure 1

Echogenicity and heterogeneity of parotid gland tumors under ultrasound. (A) Slightly hypoechogenic and slightly heterogenic pleomorphic adenoma. (B) Highly hypoechogenic and highly heterogenic WT. (C) Highly hypoechogenic and slightly heterogenic WT (D) Slightly hypoechogenic and highly heterogenic mucoepidermoid carcinoma. WT, Warthin's tumor.

Figure 2

Features of malignant tumor (mucoepidermoid carcinoma) on US, MRI and histopathology. (A) US shows an irregularly contoured mass with indistinct margins, marked hypoechogenicity and pronounced heterogeneity. (B) Color Doppler demonstrates moderate intralesional vascularity (arrow). (C) Histopathology (H&E stain): Tumor stroma with dense lymphoid infiltration, multiple cystic formations and variably distributed epithelial nests showing squamous differentiation, intermediate cells and goblet cell metaplasia. (D) Coronal T2-weighted MRI: Irregular peripheral margins with heterogeneous signal intensity and nodular components (arrows). (E) Axial T1-weighted MRI: Homogeneous hypointensity (relative to parotid gland parenchyma). (F) Short Tau Inversion Recovery sequence: Diffuse signal heterogeneity with enlarged cervical lymph nodes (arrows). US, ultrasound.

Figure 3

Features of pleomorphic adenoma on US, MRI and histopathology. (A) US: Regular contours, well-circumscribed margins (arrow) and mild hypoechogenicity. (B) Color Doppler: Homogeneous architecture without detectable vascularity. (C) Histopathology (H&E stain): Confluent sheets of epithelial/myoepithelial cells embedded in chondromyxoid stroma (arrow). (D) Coronal T2-weighted MRI: Well-defined margins (arrow) with dominant hyperintensity admixed with hypointense foci. (E) Axial T1-weighted MRI: Heterogeneous hypointensity. (F) Short Tau Inversion Recovery sequence: No abnormal lymph nodes (arrow). US, ultrasound.

Figure 4

Features of Warthin's tumor on US, MRI and histopathology. (A) US: Irregular shape, well-defined margins (arrow), marked hypoechogenicity and mild heterogeneity. (B) Color Doppler: Intense intratumoral vascularity (arrows). (C) Histopathology (H&E stain): Bilayered oncocytic epithelium forming compact tubules within lymphoplasmacytic stroma (arrow). (D) T2-weighted MRI: Balanced proportion of hyperintense and hypointense signals. (E) T1-weighted MRI: Heterogeneous hypointensity with prominent cystic components (arrow). (F) Short Tau Inversion Recovery sequence: Intralesional cystic changes (arrow); cervical lymph nodes within normal limits (arrow). US, ultrasound.

Figure 5

Features of a cyst on US, MRI and histopathology. (A) US: Irregular shape, well-defined margins, marked hypoechogenicity and moderate heterogeneity (arrow). (B) Color Doppler: Prominent intralesional vascularity (arrow). (C) Histopathology (H&E stain): Keratinizing stratified squamous epithelial lining with luminal necrotic debris (arrow). (D) T2-weighted MRI: Well-circumscribed cystic lesion with homogeneous hyperintensity (arrow). (E) T1-weighted MRI: Entirely homogeneous hyperintensity (no hypointense foci). (F) Short Tau Inversion Recovery sequence: No solid enhancement (arrow) or enlarged lymph nodes. US, ultrasound.

Figure 6

Receiver operating characteristics curve for US and MRI. AUC are 0.702 (95% CI, 0.595-0.810), 0.899 (95% CI, 0.845-0.953) and 0.841 (95% CI, 0.743-0.938) for US, MRI and US + MRI, respectively. The sensitivity and specificity of US in differentiating malignant from benign tumors were 81.8 and 52.6%, respectively. The predictive values were calculated as follows: PPV was 64.7% and negative NPV was 94.1%. The Youden Index was 0.34. For MRI, the sensitivity and specificity were 95.5 and 71.9%, respectively. The predictive values were calculated as follows: PPV was 75.8% and NPV was 95%. The Youden Index was 0.67. For US + MRI, the sensitivity, specificity, PPV and NPV were 72.7, 94.8, 84.6 and 95%, respectively. This indicates a statistically significant difference in accuracy between US and MRI, in addition to between US + MRI and US. AUC, area under the curve, US, ultrasound; NPV, negative predictive value; PPV, positive predictive value.

Figure 7

Receiver operating characteristic curves for WT and PA. Diagnostic performance metrics for differentiating WT from PA were as follows. Hypoechogenicity: AUC=0.694 (95% CI, 0.612-0.755); sensitivity, 79.6%; specificity, 88.2%; PPV, 67.8%; NPV, 71.2%. Homogeneity: AUC=0.619 (95% CI, 0.554-0.685); sensitivity, 57.1%; specificity, 35.7%; PPV, 69.4%; NPV, 64.6%. Hypoechogenity and homogeneity are the most reliable parameters for differentiating between WT and PA using ultrasound (P<0.05). AUC, area under the curve; PPV, positive predictive value; NPV, negative predictive value; WT, Warthin's tumors; PA, pleomorphic adenoma.