CASE 2111 Published on 31.03.2006

Recurrent parotid pleomorphic adenoma: US and MRI findings

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Cantisani V, Andreoli GM, Coletta L, Alfano G, D'ambrosio U

Patient

32 years, female

Categories
No Area of Interest ; Imaging Technique Ultrasound, Ultrasound-Colour Doppler, MR, MR, MR
Clinical History
A 32-year-old female presented for a routine sonographic follow-up, having a history of a total right parotidectomy performed for a pleomorphic adenoma. The sonogram showed the presence of lesions.
Imaging Findings
Three well-marginated, rounded, hypoechoic lesions, located in the right parotid region, were detected on a routine sonographic follow-up of a patient with a history of total right parotidectomy for a pleomorphic adenoma. A colour-Doppler evaluation of these lesions showed marked hypervascularisation. For further evaluation, MRI examination was performed, confirming the presence of the lesions, which were subsequently surgically removed.
Discussion
Benign epithelial salivary gland adenomas can be divided into pleomorphic and monomorphic varieties. Pleomorphic adenomas, also known as benign mixed tumours, are the most common salivary tumours and comprise almost 80% of parotid neoplasms. Pleomorphic adenoma is made up of an admixture of epithelial, myoepithelial and stromal components. Pleomorphic adenomas characteristically present as sharply marginated, ovoid, solitary lesions, whereas metastases and lymphoepithelial cysts are frequently multicentric. Although this is a benign tumour, as shown in this case and as reported in the literature, the lesion may recur and will eventually become malignant if untreated. After surgical resection, up to 43% of patients are at a risk for recurrence; recurrent disease usually occurs late: therefore, some authors claim that follow-up studies done within a span of 10 years are meaningless when reporting a lack of recurrence. However, the recurrence rate has been reported to be related with the surgical technique, with a lower rate of recurrence if a total parotidectomy is performed. The risk of malignant transformation of benign pleomorphic adenomas is 1.5% within the first five years but increases to 9.5% once the benign tumor has been present for more than 15 years. This tumour is typically superficial and occurs in a middle-aged patient, and more commonly affects women. When the tumour presents with a small size, computed tomography usually demonstrates a well-defined, spherical mass of higher density than the gland pre-contrast, with a mild to moderate contrast enhancement. When a larger mass is detected, this usually appears as an inhomogeneously enhancing soft-tissue mass, with areas of lower attenuation representing foci of degenerative necrosis and old haemorrhage. There is a great variability in the MR findings of pleomorphic adenoma, reflecting the various proportions of cellular and myxoid components. However previous studies have reported that usually pleomorphic adenomas tend to be well-defined, hypo-intense on T1-weighted images, and markedly hyper-intense on T2-weighted images, representing myxoid tissue. On STIR and diffusion weighted (DW) images, the pleomorphic adenomas show high signal intensities and high ADC values, respectively, because of the presence of myxoid components. Another diagnostic clue is the progressive enhancement on dynamic MR imaging.
Differential Diagnosis List
Recurrent parotid pleomorphic adenoma.
Final Diagnosis
Recurrent parotid pleomorphic adenoma.
Case information
URL: https://eurorad.org/case/2111
DOI: 10.1594/EURORAD/CASE.2111
ISSN: 1563-4086