MR Imaging Findings of Carcinoma Ex Pleomorphic Adenoma Related to Extracapsular Invasion and Prognosis

Black ring sign. Invasive CXPA (high-grade mucoepidermoid carcinoma) of the right submandibular gland in a 76-year-old man. MRI shows a nodule with a thick low-intensity rim (A and B, arrows) and an intra-ring component with mixed high- and low-intensity signals on axial and coronal T2WI (A and B). We defined this MRI finding as the black ring sign.

MR imaging–pathology correlation: noninvasive type. Noninvasive CXPA (salivary duct carcinoma) of the left parotid gland in a 56-year-old man. MRI showed a heterogeneous high-intensity tumor on axial T2WI (A, arrow). The corona signs on FS-T2WI and CE-FS-T1WI and the black ring sign were absent. Photomicrograph shows ductal and myoepithelial cells in the chondromyxoid stroma. A part of the tumor contained ductal and myoepithelial cells with atypical hyperchromatic nuclei. The malignant component was completely surrounded by the fibrous capsule of the pre-existing pleomorphic adenoma (B, H&E, original magnification ×20). Note higher magnification of the malignant component (C, H&E, original magnification ×100).

MR imaging–pathology correlation: invasive type. Invasive CXPA (undifferentiated carcinoma, large-cell type) of the right submandibular gland in a 72-year-old man. A huge mass replaced the right submandibular gland. MRI shows heterogeneous high intensity on T2WI and FS-T2WI (A and B, dotted arrows). Encapsulated nodules with thick low-intensity rims are present inside the tumor on axial T2WI and FS-T2WI (A and B, solid arrows). Macroscopic findings show a solid and white-yellow tumor with nodules in the nodule pattern. The nodule within the tumor corresponds to a black ring sign on MRI (C). Photomicrograph shows ductal and myoepithelial cells with atypical hyperchromatic nuclei (D, H&E, original magnification ×20). The malignant component invaded beyond the capsule (D, arrows) and infiltrated the surrounding fatty tissue. Most nodules within the tumor showed extensive hyalinization/fibrosis with myxoid stroma (D), and the black ring sign matched the hyalinization/fibrosis. The corona sign on FS-T2WI and CE-FS-T1WI reflects pathologically extracapsular tumor cells and/or inflammatory cells.