Benign pleomorphic adenoma with extensive cystic degeneration: unusual MR findings in two cases

Two cases of benign pleomorphic adenoma (PA) with extensive cystic degeneration are described. In both cases magnetic resonance (MR) imaging revealed entirely cystic tumors with an irregularity at the cyst wall. Some additional findings were observed: one case showed layering within the cyst contents caused by intratumoral hemorrhage, and the other had a small mural nodule at the cyst wall that showed very low intensity on both T1- and T2-weighted images and corresponded pathologically to the hyaline stroma. In both cases, preoperative diagnosis was difficult based on the MR findings alone. Benign PA should be included in the differential diagnosis of an entirely cystic parotid mass.