Renal inflammatory myofibroblastic tumor - a new case report.

Renal inflammatory pseudotumor is uncommon, benign tumor that has been classified into separate group but there is a risk that this lesion could be misdiagnosed. The aim of this work is to report a new case of 57-years-old man presented in our hospital with hematuria, minimal grade fever and right flank pain. Magnetic resonance imaging (MRI) and sonography revealed a tumor of the right mediorenal parenchyma, 2.5 cm in diameter. The patient underwent right nephroureterectomy under the diagnosis of renal cell carcinoma. Macroscopically examination carried out on the removed kidney showed a 2/2/1.5 cm yellowish, gelatinous, well circumscribed, mediorenal and pericaliceal mass. Fragments of the tumor were fixed in 10% formaldehyde, included in paraffin, and the sections were stained with HE, VG and immunohistochemically with vimentin (VIM), MNF116, SyN, smooth muscle actin (ACT), desmin, CD68, S100, HMB45, and CD117. The histological examination revealed a compact spindle cell proliferation, a hypocellular fibrous area in an edematous myxoid background infiltrated by small lymphocytes, histiocytes, some plasma cells and small bone area. The spindle cells were diffuse positive for VIM, ACT, CD68 and negative for desmin, MNF116, SyN, S100, HMB45, and CD117. The pathologic diagnosis was renal inflammatory pseudotumor, raising the problem of differential diagnosis, as the clinical and imagistic aspects are similar to those of a renal carcinoma and the problem in establishing a preoperative correct diagnosis.