I saw the sign: The black ring sign in carcinoma ex pleomorphic adenoma.
Sinem Saydam, Ibrahim Salih Gecer, Sena Sebnem Boz et al.
✦ AI-curated · Sources linked
Case in brief
Two patients had carcinoma ex pleomorphic adenoma arising in the left submandibular and left parotid glands. In both tumors, T2-weighted MRI showed a conspicuously thick, hypointense rim around an intratumoral component, termed the black ring sign. Maximum rim thicknesses were 2.9 mm and 2.4 mm; mean apparent diffusion coefficient values were 1.33 × 10⁻³ mm²/s and 1.20 × 10⁻³ mm²/s, respectively. Histopathology linked the rim to fibrotic and hyalinized stroma associated with the pleomorphic adenoma component. Both tumors were invasive, although the corona sign was absent.
What made this case unusual
The black ring sign was present in both tumors, while the corona sign was absent despite pathologically confirmed invasion. The T2-hypointense rim corresponded to fibrotic and hyalinized stromal change.
Diagnostic / clinical pearl
A thick T2-hypointense rim may support preoperative consideration of carcinoma ex pleomorphic adenoma, but it is not pathognomonic; interpret it alongside tumor morphology, diffusion characteristics, clinical findings, and radiologic-pathologic correlation.