Oncocytoma: the vanishing parotid mass

Abstract

Parotid gland oncocytoma is an uncommon, benign salivary neoplasm composed of mitochondria-rich oncocytes. The purpose of this study was to correlate MR imaging and histopathology of parotid gland oncocytomas and to define the features that may distinguish these neoplasms from other benign and malignant parotid gland tumors. The MR imaging features in 9 patients with a pathologic diagnosis of oncocytoma were retrospectively reviewed. The imaging features were strikingly similar for 8 of the 9 patients. All lesions appeared T1 hypointense but isointense to the native parotid gland on fat-saturated T2 and postcontrast T1 imaging. On MR imaging, parotid gland oncocytomas share specific imaging characteristics that have not been described for benign or malignant parotid gland tumors. Oncocytomas are isointense to native parotid gland on fat-saturated T2 and T1 postcontrast MR images. Preoperative identification of correct histology may help surgical planning.

Fig 1.

Case 1, 62-year-old female with 2-year history of firm, painless left parotid mass. A, Axial T1-weighted MR image shows a well-demarcated mass within the superficial lobe of the left parotid gland (white arrow) that is T1 hypointense. B, Axial T2-weighted MR image with fat saturation shows the mass (white arrow) to be isointense to the native parotid gland. C, Axial T1-weighted postgadolinium sequences illustrates the mass (white arrow) as isointense to the native parotid gland.

Fig 2.

Case 5, 55-year-old woman with painless “lump” behind her left ear. A, Axial T1-weighted MR image shows a well-demarcated mass within the superficial and deep lobe of the left parotid gland (white arrow) that is T1 hypointense. B, Axial T2-weighted MR image with fat saturation illustrates the mass (white arrow) to be isointense to the native parotid gland. C, Axial T1-weighted postgadolinium sequence shows the mass (white arrow) as isointense to the native parotid gland.

Fig 3.

Case 7, 75-year-old man with history of squamous cell carcinoma of the larynx status postradiation found to have an enlarging mass in the left parotid gland on surveillance imaging. A, Axial T1-weighted MR image shows a well-demarcated mass within the superficial lobe of the left parotid gland (white arrow) that is T1 hypointense. B, Axial T2-weighted MR image with fat saturation shows the mass to be hyperintense but heterogeneous to the native parotid gland. C, Axial T1-weighted postgadolinium sequence shows the mass (white arrow) to demonstrate heterogeneous enhancement to the native parotid gland.

Fig 4.

Typical histologic features of a parotid gland oncocytoma including eosinophilic cells with finely granular cytoplasm and uniform, round, centrally placed nuclei (hematoxylin-eosin stain, original magnification, ×400).