Epithelioid Myoepithelioma of the Accessory Parotid Gland: Pathological and Magnetic Resonance Imaging Findings

Abstract

Tumors of the accessory parotid gland (APG) are rare, and pleomorphic adenoma (PA) is the most common benign APG tumor subtype. Myoepithelioma of the APG is much rarer than PA, and to date, only 5 cases have been sporadically reported in the English literature. We describe the clinicopathological and MRI findings of an epithelioid myoepithelioma of the APG that was treated in our hospital. The patient's only clinical symptom was a slow-growing and painless mid-cheek mass. The tumor was suspected to be PA before surgery based on the following MRI findings: (1) a well-circumscribed and lobulated contour, (2) isointensity and hyperintensity relative to the muscle on T1- and T2-weighted images (WIs), respectively, (3) good enhancement on contrast-enhanced T1-WIs, (4) peripheral hypointensity on T2-WIs, and (5) a gradual time-signal intensity curve enhancement pattern on gadolinium-enhanced dynamic MRI. The tumor was completely resected via a standard parotidectomy approach, and the postoperative pathological examination of the tumor, including immunohistochemistry, confirmed the diagnosis of epithelioid myoepithelioma. As it is hardly possible to distinguish myoepithelioma from PA and low-grade malignant tumors preoperatively, a pathological examination using frozen sections is helpful for surgical strategy-related decisions.

Myoepithelioma of the Parotid Gland: A Case Report with Review of the Literature and Classic Histopathology

“…Myoepitheliomas only account for approximately 1% of all salivary neoplasms [ 3 ]. Primarily they will affect the parotid gland (~40%) and minor salivary gland sites (~21%) [ 7 – 10 ].…”

“…In total, myoepitheliomas only account for 1% of all salivary gland neoplasms. The overwhelming majority of myoepitheliomas are benign but malignant transformation can take place in recurrent cases and cases left untreated [ 1 – 3 ]. We present the first known case, to the best of our knowledge, at our institution of myoepithelioma occurring in the left parotid gland.…”

Myoepithelioma of parotid gland – a diagnosis of immunohistochemistry

“…It is a rare benign mass arising from neoplastic myoepithelial or basket cells, which are found between the basement membrane and the basal plasma membrane of acinar cells. Myoepitheliomas only account for approximately 1% of all salivary neoplasms [4]. Primarily they will affect the parotid gland (~40%) and minor salivary gland sites (~21%) (11).…”

“…The overwhelming majority of myoepitheliomas are benign but malignant transformation can take place in recurrent cases and cases left untreated [2,3,4].…”

Influence of amplitude‐related perfusion parameters in the parotid glands by non‐fat‐saturated dynamic contrast‐enhanced magnetic resonance imaging

“…It has been proven useful in differentiating parotid tumors, 1-10 quantifying parotid microvascular characteristics in inflammatory diseases 11 and autoimmune diseases, 12 characterizing radiation-induced perfusion changes of the parotid glands, [13][14][15][16][17][18] and evaluating parotid function after gustatory stimulation. 19 Information regarding perfusion in the parotid glands can be obtained using various MRI techniques, including dynamic contrast-enhanced (DCE) MRI, [1][2][3][4][5][6][7][8][11][12][13][14][15][16] arterial spin labeling MRI, 19 and intravoxel incoherent motion MRI. 9,17,18 In DCE-MRI specifically, a series of images after intravenous administration of gadolinium (Gd) chelates are dynamically acquired for several minutes.…”