Basal cell adenoma of the parotid gland: MR imaging findings with pathologic correlation

Abstract

Background and purpose: Basal cell adenomas (BCAs) are rare tumors of the parotid gland. Only a few case reports describing MR imaging features of BCA have been published. The aim of this study was to describe and characterize the MR findings of BCAs of the parotid gland.

Materials and methods: We retrospectively reviewed MR images of BCA with pathologic correlation in 8 cases (2 men and 6 women; age range, 52-82 years) collected between January 1992 and August 2004 from our pathologic data base. All MR images were retrospectively evaluated with respect to the marginal morphology, signal intensity (SI), and enhancement behavior by 2 experienced radiologists.

Results: On pathologic examination, 5 tumors were solid type, 2 were trabecular type, and 1 was membranous type. All of the tumors were well circumscribed with smooth contours. Cystic changes were seen in 4 cases. On T1-weighted images (T1WI), 7 tumors showed homogeneously low SI equal to muscle and one showed heterogeneously low SI. On T2-weighted images (T2WI), all of them showed slightly lower SI than that of surrounding parotid tissue. On gadolinium-enhanced T1WI, 6 tumors demonstrated moderate enhancement and one demonstrated strong enhancement (membranous type). Dynamic studies were performed in 4 cases. All showed rapid and prolonged enhancement.

Conclusion: MR imaging findings of BCA were well-defined and smooth marginal morphologies, relatively low SI on both T11W and T2WI, and rapid and prolonged enhancement on dynamic study. Although BCAs are rare, they should be suspected when a tumor shows all of the characteristics noted here.

Fig 1.

A 82-year-old man with basal cell adenoma (BCA) (membranous type, marked enhancement) A, A T1-weighted image (T1WI) shows a homogeneously low-SI mass with a well-defined, smooth margin in the superficial lobe of the left parotid gland. B, On T2WI, the tumor shows slightly lower SI than the normal parotid gland. C, On Gd-enhanced fat-suppressed T1WI, the tumor shows homogeneous and strong enhancement. D, On dynamic study, the tumor shows a rapid and prolonged enhancement pattern. E, Microscopic examination (hematoxylin-eosin stain [H&E]) shows conspicuous hyaline matrix surrounding epithelial cells. Relatively large vessels are seen in the tumor (arrows).

Fig 2.

A 68-year-old woman with basal cell adenoma (BCA) (solid type, large cystic change) A, A T1-weighted image (T1WI) shows a homogeneously low-SI mass with well-defined and smooth margin in the deep lobe of the right parotid gland. B, On T2WI, the tumor shows slightly lower SI than the normal parotid gland with very high SI (cystic change) at the anterior half of the tumor. C, On Gd-enhanced T1WI, the tumor shows homogeneous moderate enhancement of the solid component. On T2WI, a very-high-SI area is not enhanced. D, Microscopic examination (hematoxylin-eosin stain [H&E]) shows a solid pattern with many microcystic changes around a large cystic change. Dilated vascular channels are prominent.

Fig 3.

A 69-year-old woman with basal cell adenoma (BCA) (trabecular type) A, A T1-weighted image (T1WI) shows a homogeneously low-SI mass with a well-defined, smooth margin in the left parotid gland. B, On Gd-enhanced T1WI, the tumor shows inhomogeneous moderate enhancement. C, On dynamic study, the tumor shows rapid enhancement at the periphery of the tumor and is gradually enhanced from the periphery to central part of the tumor. D, Microscopic examination (hematoxylin-eosin stain [H&E]) shows a trabecular pattern of a BCA. The tumor is composed of small uniform basaloid cells (arrowheads) arranged in solid or trabecular pattern. The stroma is loose, scantily collagenous tissue. There is characteristic palisading (arrows) in the peripheral portion of the tumor cell nests.