Differential diagnosis of parotid gland tumours: which magnetic resonance findings should be taken in account?

Abstract

Our aim was to define typical magnetic resonance (MRI) findings in malignant and benign parotid tumours. This study is based on retrospective evaluation of pre-surgical MRI of 94 patients with parotid gland tumours. Histology results were available for all tumours. There were 69 cases of benign (73%) and 25 cases of malignant (27%) tumours, including 44 pleomorphic adenomas, 18 Warthin's tumours, 7 various benign tumours, 6 squamous cell carcinomas, 3 carcinoma ex pleomorphic adenomas, 2 mucoepidermoid carcinomas, 1 adenoid cystic carcinoma and 13 various malignant tumours. The following MRI parameters were evaluated: shape, site, size, margins, signal intensity (SI) on T1w and T2w images, contrast enhancement, signal of cystic content, presence or absence of a capsule, perineural spread, extraglandular growth pattern and cervical adenopathy. Statistical analysis was performed to identify the MRI findings most suggestive of malignancy, and to define the most typical MRI pattern of the most common histologies. Ill-defined margins (p < 0.001), adenopathies (p < 0.001) and infiltrative grown pattern (p < 0.001) were significantly predictive of malignancy. Typical findings of pleomorphic adenoma included hyperintensity on T2w images (p = 0.02), strong contrast enhancement (p < 0.001) and lobulated shape (p = 0.04). Typical findings of Warthin's tumour included hyperintense components on T1w images (p < 0.001), location in the parotid inferior process (p < 0.001) and mild or incomplete contrast enhancement (p = 0.01). SI on T1w and T2w images and contrast enhancement enables differential diagnosis between pleomorphic adenoma and Warthin's tumour.

Keywords: Differential diagnosis; Histology; Magnetic Resonance Imaging; Neoplasms; Parotid gland.

Fig. 1.

Squamous carcinoma of the left parotid gland. (a) Axial T2w image, (b) axial T1w image and (c and d) axial T1w fat-sat image after contrast injection. The left intraparotid tumour appeared hypointense on T2w and isointense on T1w images (arrowheads) with ill-defined margins. After contrast injection (on T1w fat-sat image), the tumour showed a strong enhancement, encasing the external carotid artery (arrow). Cervical adenopathies were also evident in levels IIa and IIb on the left side (thick arrows).

Fig. 2.

Pleomorphic adenoma of the right parotid gland. (a) Coronal T2w image, (b) axial T2w fat-sat image, (c) axial T1w image and (d) axial T1w fat-sat image after contrast injection. The right intraparotid tumour appeared as an oval lesion, hyperintense on T2w images, and isointense on T1w images, with sharp margins and homogeneous SI. After contrast injection, the lesion showed strong enhancement that was higher than that seen in normal parotid tissue.

Fig. 3.

Warthin's tumour of the left parotid gland. (a) Coronal T2w image, (b) axial T2w fat-sat image, (c) axial T1w image and (d) axial T1w fat-sat image after contrast injection. The left intraparotid tumour appeared as an oval lesion with welldefined margins and hypointense on T2w images. T1w images showed a hyperintense cystic area (arrow) within the lesion. After contrast injection, the lesion showed only focal contrast enhancement.

Fig. 4.

Atypical pleomorphic adenoma of the right parotid gland. (a) Axial T2w image, (b) axial T2w fat-sat image, (c) axial T1w image and (d) axial T1w fat-sat image after contrast injection. The lobulated tumour involved both the superficial and the deep lobe of the right parotid gland, showing sharp margins and inhomogeneous SI on T2w images. After contrast injection, the lesion showed strong inhomogeneous enhancement.