Pancake kidney, a rare and often misdiagnosed malformation: a case report and radiological differential diagnosis.

Renal ectopia and fusion anomalies are Congenital Anomalies of the Kidney and the Urinary Tract (CAKUT) that are usually incidentally detected and asymptomatic. Patients affected present a higher risk of complications like recurrent urinary tract infections or obstruction. Pancake kidney (PK) is one of the rarest types of renal anomaly with complete fusion of the superior, mild and inferior poles of both kidneys in the pelvic cavity. Each kidney has its own excretory system with two ureters that do not cross the midline. In the asymptomatic cases, a conservative approach should be performed. Surgical management may be needed when urological problems occur. PK is often associated with congenital anomalies of other organs. Ultrasound is the first line radiological examination for the diagnosis and the follow-up of kidney malformations. The main sonographic findings suggesting PK diagnosis are a large and lobulated renal mass consisting of two fused lateral lobes without an intervening septum located in the pelvic cavity. Each lobe usually has a separate pelvicalyceal system, the renal pelvis is anteriorly placed and the ureters are usually short and enter the bladder normally without crosses the midline. Ultrasonography gives useful information on the morphology and volume of the organ, and on its vascularization through the use of the Color- and Power-Doppler. Computer Tomography and Magnetic Resonance Urography are second level techniques used to confirm the diagnosis and to evaluate the presence of other abnormalities. The knowledge of the imaging findings and the anatomy of congenital renal malformations is important to avoid diagnostic pitfalls and misinterpretations. We report the case of a 14-years old female with PK who was misdiagnosed with a horseshoe kidney (HSK) during an abdominal ultrasound.