Horseshoe kidney presenting as a retroperitoneal mass. Report of a case diagnosed by fine needle aspiration cytology.

BACKGROUND: Horseshoe kidney is a renal congenital anomaly. It is the result of the fusion of either upper or lower poles of both kidneys, appearing as a horseshoe-shaped structure. This anomaly is very frequent: it can be found in about 1 of every 50-1,000 autopsies). CASE: Computed tomography performed routinely after pancreatitis in a 37-year-old female showed a retroperitoneal mass of uncertain origin. Fine needle aspiration cytology (FNAC) smears evidenced normal renal tissue. Urography confirmed the diagnosis of horseshoe kidney. CONCLUSION: This is the first reported case of horseshoe kidney diagnosed by FNAC. It demonstrates the utility of FNAC for diagnosis of retroperitoneal masses, especially if they are asymptomatic.