Multiparametric MRI in Diagnosis of Parotid Gland Tumor: An Observational Study in 3-T MRI

Abstract

Background Preoperative magnetic resonance imaging (MRI) has an important role in the management and prognostication of parotid gland tumors. We aim to evaluate the role of multiparametric MRI in differentiating the major subgroup of parotid tumors. Materials and Methods Multiparametric MRI: T1-weighted imaging (T1WI), T2WI, diffusion-weighted imaging (DWI), pseudo-continuous arterial spin labeling (ASL) and dynamic contrast-enhanced (DCE) imaging were acquired in all patients. Apparent diffusion coefficient (ADC) values and tumor blood flow (TBF) were calculated from DWI and ASL, respectively. Ktrans, Kep, Ve, initial area under the gadolinium enhancement concentration curve (IAUGC), maximum slope, and contrast enhancement ratio (CER) were calculated from DCE-MRI perfusion. The above parameters were compared between three major subgroups of parotid gland tumors, such as non-Warthin benign tumors (NWBT), Warthin's tumors (WT), and malignant parotid tumors (MT). Results The mean ADC of MT ( n = 13), WT ( n = 5), and NWBT ( n = 29) was 1.03 × 10 ^-3 mm ² /s, 0.97 × 10 ^-3 mm ² /s, and 1.89 × 10 ^-3 mm ² /s, respectively. The mean TBF (in mL/100 g/min) was the highest MT (70.33), followed by WT (62.04) and NWBT (21.99). A cutoff of 40.51 mL/100 g/min showed a sensitivity of 96.6% and specificity of 77.8% for predicting NWBT. In DCE-MRI, 96.6% of the NWBT showed a type A time-signal intensity curve. Although the majority of MT and WT had type C and B curves, respectively, there was overlapping. Among the quantitative DCE parameters, Ktrans and Kep were highly sensitive for differentiating NWBT, WT, and MT. Ktrans, Kep, IAUGC, and MS were maximum in WT, followed by MT and NWBT. Kep and Ktrans both had an accuracy of 84.7% for predicting pleomorphic adenoma. Conclusion Multiparametric MRI is useful for differentiating NWBT, WT, and MT. DCE-MRI helps in differentiating benign from malignant tumors. DWI and ASL are useful in differentiating NWBT from parotid malignancy.

Keywords: arterial spin labeling; diffusion-weighted MRI; dynamic contrast enhanced MRI; parotid tumor; salivary gland tumor.

Fig. 1

Receiver operating characteristic (ROC) curve of ( A ) apparent diffusion coefficient (ADC) and ( B ) tumor blood flow (TBF) for diagnosis of non-Warthin's benign tumors. ADC from diffusion-weighted imaging is showing sensitivity of 93.1% and specificity of 88.9% (area under the curve [AUC]: 0.941) and TBF from arterial spin labeling showing sensitivity of 96.6% and specificity of 77.8% (AUC: 0.880).

Fig. 2

Magnetic resonance imaging (MRI) of a 62-year-old woman having pleomorphic adenoma of the left parotid gland. Axial ( A ) T1-weighted imaging (T1WI), ( B ) T2WI, and ( C ) short tau inversion recovery (STIR) images show a well-defined rounded lesion involving the superficial lobe of the left parotid gland, which is hypointense on T1 and hyperintense on T2 and STIR. The lesion is hyperintense on both ( D ) diffusion-weighted imaging and ( E ) apparent diffusion coefficient, suggesting facilitated diffusion. ( F ) Arterial spin labeling shows reduced perfusion. ( G ) Postcontrast T1WI shows heterogeneous enhancement. ( H ) On dynamic contrast-enhanced MRI (DCE-MRI), type A time-intensity curve seen. Quantitative DCE shows a ( I ) low Ktrans (0.165/min), ( J ) high Ve (0.89), ( K ) low Kep (0.187/min), ( L ) low IAUGC (0.192), ( M ) CER (2.224), and ( N ) low MS (0.0195), ( O ) histopathological examination showed epithelioid, myoepithelial, and stromal components suggestive of pleomorphic adenoma. CER, contrast enhancement ratio; IAUGC, initial area under the gadolinium enhancement concentration curve; MS, maximum slope.

Fig. 3

Magnetic resonance imaging (MRI) of the parotid gland in a 31-year-old woman with Warthin's tumor (WT) of the right parotid gland. Axial ( A ) T1-weighted imaging (T1WI), ( B ) T2WI, and ( C ) short tau inversion recovery (STIR) images show a well-defined lobulated lesion with T1 hyperintense cystic areas, and heterogeneous signal on T2 and STIR. ( D ) Postcontrast T1WI shows heterogeneous enhancement. ( E ) Diffusion-weighted imaging and ( F ) apparent diffusion coefficient show restricted diffusion. ( G ) Arterial spin labeling shows increased perfusion. ( H ) On dynamic contrast-enhanced MRI (DCE-MRI), type B time-intensity curve noted. Quantitative DCE show a ( I ) high Ktrans (1.068/min), ( J ) low Ve (0.25), ( K ) high Kep (4.387/min), ( L ) high IAUGC (0.427), ( M ) CER (1.714), and ( N ) high MS (0.0515), ( O ) HPE display glandular architecture with extensive lymphoid stroma surrounding cystic regions with papillary projections bordered by oncocytes suggestive of WT. CER, contrast enhancement ratio; IAUGC, initial area under the gadolinium enhancement concentration curve; MS, maximum slope.

Fig. 4

Magnetic resonance imaging (MRI) of the parotid gland in a 64-year-old man with acinic cell carcinoma of the left parotid gland. Axial ( A ) T1-weighted imaging (T1WI), ( B ) T2WI, and ( C ) short tau inversion recovery images show an irregular lobulated lesion with heterogeneous signal and areas of cystic change. ( D ) Diffusion-weighted imaging and ( E ) apparent diffusion coefficient show restricted diffusion. ( F ) Arterial spin labeling shows increased perfusion. ( G, H ) Postcontrast T1WI shows heterogeneous enhancement and perineural spread along the mandibular division of left trigeminal nerve. ( I ) Quantitative dynamic contrast-enhanced (DCE) shows a high Ktrans (0.634/min), ( J ) low Ve (0.54), ( K ) high Kep (1.23/min), ( L ) high IAUGC (0.554), ( M ) CER (1.845), and ( N ) high MS (0.0834). ( O ) On DCE-MRI, type C time-intensity curve is seen. CER, contrast enhancement ratio; IAUGC, initial area under the gadolinium enhancement concentration curve; MS, maximum slope.

Fig. 5

Bar diagram showing ( A ) type of the time signal intensity curve and ( B ) quantitative dynamic contrast-enhanced (DCE) parameters in non-Warthin's benign tumor, Warthin's tumor, and malignant tumor of the parotid gland. CER, contrast enhancement ratio; IAUGC, initial area under the gadolinium enhancement concentration curve; MS, maximum slope.