Mucinous adenocarcinoma derived from villous adenoma of the kidney with muconephrosis.

Upper respiratory tract villous adenoma (VA) with muconephrosis is rare and should be included in the differential diagnosis when pelvic dilatation with a solid component is detected. VA may transform into malignant mucinous adenocarcinoma, which should be suspected if contrast enhancement on computed tomography (CT)/magnetic resonance imaging (MRI) and restricted diffusion on MRI are observed.