Diagnosing common parotid tumours with magnetic resonance imaging including diffusion-weighted imaging vs fine-needle aspiration cytology: a comparative study

Abstract

Objectives: the purpose of this study was to evaluate the accuracy of MRI combined with diffusion-weighted imaging (DWI) vs fine-needle aspiration cytology (FNAC) in diagnosing common parotid masses.

Methods: 25 consecutive patients (mean age 61 years) with parotid masses were included in this study. Informed consent and ethical approval was obtained. 22 patients underwent both MRI combined with DWI and FNAC. From DWI data, apparent diffusion coefficient maps were generated. The MRI study protocol consisted of T(1) weighted spin echo; T(2) weighted and T(2) weighted fat-suppressed turbo spin echo; DWI; and T(1) weighted fat-suppressed post-contrast images. MRI and FNAC diagnoses were compared with histopathology. Youden's index was used to compare the two methods.

Results: masses comprised eight Warthin tumours, eight adenomas (six pleomorphic adenomas, two basal cell adenomas), five carcinomas, two lipomas, one haemagioma and one benign lymphadenopathy. Technically, MRI was successful in 24 of the 25 patients (96%), FNAC was successful in 20 of the 23 patients (87.0%). The accuracy, sensitivity and specificity of MRI without DWI were 96%, 80% and 100%, respectively. Diagnostic accuracy did not increase by adding DWI to conventional MRI; however, DWI was helpful for diagnosing benign tumour histology. MRI combined with DWI was successful for determining accurate tumour typing in all benign masses except one lymphadenopathy. When FNAC had adequate material the accuracy, sensitivity and specificity were 95%, 75% and 100%, respectively. Youden's index was 0.80 for MRI and 0.75 for FNAC.

Conclusions: MRI combined with DWI seems to have similar diagnostic potential as FNAC in differentiation of benign vs malignant parotid masses.

Figure 1

A pleomorphic adenoma in the superficial lobe of the left parotid gland of a 70-year-old woman. (a) An axial T1W image (500/14, TR/TE) showing a mass lesion that is hypointense (arrow) to gland parenchyma and isointense compared with muscle. (b) An axial T2W image (3800/90, TR/TE) showing a mass lesion that is isointense (arrow) with gland parenchyma and hyperintense compared with muscle. (c) An apparent diffusion coefficient (ADC) map showing a solid lesion (arrow) with high ADC (1.54×10⁻³ mm² s⁻¹). (d) An image of fine-needle aspiration cytology (FNAC) showing spindle-shaped mesenchymal cells intermingled with epithelial cells (haematoxylin and eosin ×20 original magnification). (e) A histological section of the tumour showing biphasic appearance of pleomorphic adenoma resulting from the intimate admixture of epithelium and stroma separated from the surrounding salivary gland tissue by an intact fibrous capsule (haematoxylin and eosin ×10 original magnification)

Figure 2

A Warthin tumour involving the superficial and deep lobes of the right parotid gland of a 60-year-old man. (a) An axial T1W image (500/14, TR/TE) showing a hypointense mass lesion (arrow) relative to gland parenchyma and isointense to muscle, enclosed in a rim of low signal in the posterior portion of the mass. (b) An axial T2W image (3800/90, TR/TE) showing a hypointense mass lesion (arrow), relative to the gland parenchyma and isointense to muscle, enclosed in a rim of low signal in the right lateral portion of the mass. (c) An apparent diffusion coefficient (ADC) map image showing the lesion (arrows) with low ADC of 0.62 × 10⁻³ mm² s⁻¹. (d) An image of fine-needle aspiration cytology (FNAC) showing flat sheets of oncocytic cells surrounded by lymphocytes (haematoxylin and eosin × 20 original magnification). (e) A histological section of the tumour showing lymphoid stroma surrounded by large epithelial cells with oncocytic features arranged in two layers (haematoxylin and eosin ×10 original magnification)

Figure 3

An adenocarcinoma located in the deep lobe of the left parotid gland of a 62-year-old man. (a) A non-contrast axial T2W image (3800/90, TR/TE) showing a heterogeneous hypointense mass (arrows) relative to the gland parenchyma. Note the ill-defined contour of the lesion. (b) A non-contrast axial T1W image (500/14, TR/TE) showing mass (arrows), hypointense to gland parenchyma. (c) An apparent diffusion coefficient (ADC) map image showing the lesion (arrows) with an intermediate ADC of 1.19 × 10⁻³ mm² s⁻¹. (d) An image of FNAC showing a cluster of pleomorphic and atypical epithelial cells (hematoxylin and eosin × 20 original magnification). (e) A histological section of the tumour showing adenocarcinoma infiltration in desmoplastic stroma (hematoxylin and eosin × 20 original magnification)