Isolated renal hydatid cyst misdiagnosed and treated as a cystic renal tumor: a diagnostic pitfall

Background The hydatid disease is a parasitic infestation caused by the larval stage of Echinococcus granulosus. The renal location of this infectious disease is uncommon compared to hepatic or pulmonary ones. Most patients remain asymptomatic for years and hydatiduria is the only pathognomonic clinical symptom. We report a rare case of renal hydatid cyst misdiagnosed and treated as a renal tumor. Case presentation A 45-year-old woman with no significant medical or surgical history presented with left lumber pain with hematuria. Magnetic Resonance Imaging (MRI) displayed a left renal mass with cystic and solid components, showing discreet enhancement, classified as Bosniak IV. The diagnosis of renal malignant tumor was made. The patient underwent a lumbotomy. Intraoperatively, the mass was adherent to the perirenal fat and seemed to invade the adrenal gland. An enlarged left nephrectomy with surrenalectomy was performed. The gross specimen showed a superior polar renal cyst (9 × 7 × 6cm). The cyst had a thick wall and contained multiple internal smaller cysts recalling the appearance of the hydatid cyst. The microscopic study showed a cyst wall consisting of acellular eosinophilic laminated membrane lined by a thin germinal layer from which merge daughter cysts. This cyst wall is surrounded by a dense fibrovascular tissue with chronic inflammatory cells. The diagnosis of renal hydatic cyst was made. Conclusion Although the renal hydatid cyst is relatively rare, this diagnosis must be considered in patients with renal cystic masses, especially endemic countries. Preoperative diagnosis is challenging, especially in type IV cysts which can mimic a renal tumor and lead to overtreatment.