Teaching Case

A 44-year-old male patient referred with a slowly-growing lump on his right cheek over the last six months. Physical examination revealed a lobulated mass lesion probably within the superficial lobe of parotid gland.

A 44-year-old male patient referred with a slowly-growing lump on his right cheek over the last six months. Physical examination revealed a lobulated mass lesion probably within the superficial lobe of parotid gland. A sonographic examination of the lesion was followed by an MRI study of the parotid area which was performed on a 1.5 T MR scanner, with SE T1, FSE T2, fat-suppressed FSE T2, post-gadolinium SE T1, fat-suppressed SE T1 sequences on three planes. Sonography and MR pictures revealed a well circumscribed mass lesion with some inhomogeneity, and intense gadolinium enhancement on MRI, within the superficial lobe of parotid gland. The mass lesion was removed surgically.

The majority of salivary gland tumors are found in the parotid gland, and 75-80 % of parotid gland tumors are benign. Pleomorphic adenoma (benign mixed tumor) is the most common neoplasm of the salivary glands, representing 60-80 % of all salivary glands and 80 % of parotid tumors. Pleomorphic adenoma clinically presents as a slowly-growing lump in cheek. It is usually observed in patients more than 50 years. It may be seen as a round, oval or lobulated sharply marginated mass, most often located lateral to the plane of facial nerve.Facial nerve position is lateral to retromandibular vein, which separates the superficial portion of the parotid gland from the deep portion. Histopathologically the neoplasm contains a mixture of epithelial and myoepithelial cells, and rarely dystrophic calcifications. Imaging modalities used for the diagnosis of pleomorphic adenoma are sonography, computed tomography (CT), and magnetic resonance imaging (MRI). In small neoplasms less than 3 cm, sonography reveals well-delineated hypoechoic nodule with mild posterior enhancement. In larger tumors, inhomogeneity related to necrosis, cystic, or hemorrhagic changes and ill-defined limits make the diagnosis difficult. Peripheral flow signal patterns may be observed with color Doppler sonography. The neoplasm is smoothly marginated, well defined, and hyperdense due to mucoid matrix compared with the surrounding gland on CT. The lesion shows variable contrast enhancement. Small lesions are usually homogeneous, whereas larger ones tend to be inhomogeneous. Calcification also may be present as indistinct margins in case of surrounding inflammation or hemorrhage. The signal intensity is generally lower than that of the surrounding tissue on T1-weighted images on MRI. On T2-weighted MR images, the larger the tumor, the more inhomogeneous it appears, but usually it is quite hyperintense. After gadolinium injection, the use of a fat suppressed technique is preferred to increase the visibility of the lesion. However histopathologic diagnosis of salivary gland tumors cannot be predicted reliably by means of imaging findings. Treatment is surgical resection of the tumor. Enucleation or insufficient removal of the tumor results in recurrence in at least 20 % of the cases.