We report a case of a 73-year-old man with inflammatory pseudotumor of the left renal pelvis. The tumor was histologically composed of spindle-shaped cells with mild atypia and some multinucleated giant cells, lymphocytes and plasma cells. Cytological features revealed spindle-shaped fibroblast-like cells with enlarged oval nuclei with slight atypia. These cells had thin nuclear membranes and a fine chromatin structure. Imprint smears also contained lymphocytes and foreign-body type multinucleated giant cells. Immunostaining was positive for α-SMA and vimentin. These features were thought to be compatible with those reported for inflammatory pseudotumor. Its cytological differential diagnosis was briefly discussed as well.
