Diagnosis of renal malacoplakia by fine needle aspiration cytology. A case report.

BACKGROUND: Malacoplakia is a rare chronic inflammatory disease first described by von Hansemann in 1901. L. Michaelis and M. Gutmann published the first report in 1902, describing the characteristic round intracellular and extracellular inclusions, or Michaelis-Gutmann bodies. Renal malacoplakia is a form of chronic tubulointerstitial nephritis the clinical and radiologic findings of which are often suggestive of a neoplasm. Renal malacoplakia may be related to megalocytic interstitial nephritis and xanthogranulomatous pyelonephritis.

CASE: A 67-year-old male presented with acute left loin pain suggestive of uretery colic. The past medical history was unremarkable and physical examination within normal limits. Renal ultrasound and computed tomography showed a 3.5-cm, cystic mass with a thickened, irregular wall located centrally within the left renal sinus. The size of the left kidney was 11.5 cm. A renal arteriogram provided no evidence of a vascular mass of any type. Fine needle aspiration (FNA) revealed many large, foamy, granular macrophages with large, eccentric nuclei and prominent nucleoli containing round inclusions that exhibited a laminated appearance, consistent with the structure of Michaelis-Gutmann bodies. Many were also present extracellularly.

CONCLUSION: To our knowledge this is the first case of renal malacoplakia diagnosed by fine needle aspiration. This case demonstrates the value of FNA in determining the nature of a radiologically nonspecific lesion. It highlights the value of FNA as a substitute for or preliminary method before more invasive procedures in the diagnosis of a treatable disease entity.