Retroperitoneal malakoplakia mimicking sarcoma: a case report

This report describes a rare case of retroperitoneal malakoplakia in a 70-year-old woman. The patient underwent open nephrectomy under suspicion of a huge retroperitoneal malignancy invading the right kidney. The mass was attached to the capsule of the lower pole of the kidney. Microscopically, the mass was composed of solid sheets of mononuclear cells and variable numbers of chronic inflammatory cells. Round basophilic structures known as Michaelis-Gutmann bodies were found within the mononuclear cells and extracellularly in the stroma. The mononuclear cells were immunohistochemically positive for CD68, indicating that these cells were histiocytes. Because the patient was preoperatively diagnosed with retroperitoneal malignancy, surgery was performed. Malakoplakia should be included in the differential diagnosis of retroperitoneal masses.