Inflammatory myofibroblastic tumor of the perirenal soft tissue misdiagnosed as renal cell carcinoma

Inflammatory myofibroblastic tumor (IMT) of the kidney or perirenal soft tissue is a rare benign lesion that can mimic a malignant renal neoplasm. We describe the case of a 51-year-old woman that had originally been misdiagnosed as renal cell carcinoma in another hospital. Histologic re-evaluation of the tumor in our institution showed that it was in fact an IMT. Awareness of this entity is required for rendering the accurate diagnosis. An association with inflammatory infiltrate, frequent erythrocyte extravasations, edematous or myxoid stroma, absence of atypical mitosis, and the results of a detailed immunohistochemical panel might help in the differential diagnosis. Our patient is recurrence-free in the 18th month of post-operative follow-up.