Renal hydatid cyst mimicked cystic renal cell carcinoma: A case report

Hydatid cyst (HC) is a zoonotic parasitic disease in agricultural and pastoral areas while renal involvement without liver and lung hydatid is both less common in clinical practice and rarely described in literature. We present a case of a 40‐year‐old male from Xinjiang who complained of flank pain in the right with oliguria. Robot‐assisted laparoscopic exploration, conversion to open laparotomy and excision of internal capsule in right kidney were performed. Finally, a typical renal HC was diagnosed after complementary examinations. Isolated renal HC is very rare and can be misinterpreted as a cystic renal cell carcinoma pre‐operatively.


| INTRODUCTION
Hydatid cyst (HC) is a zoonotic parasitic disease mainly caused by the larvae of Echinococcus granulosus. The definitive hosts of the parasite are usually dogs, or some other dog-like carnivores while the intermediate hosts are mostly the livestock such as sheep and cows. Humans acquire the infection when they consume the food or water contaminated with dog feces containing parasite eggs. The disease is endemic in areas with developed animal husbandry all over the world, such as the Mediterranean area, Africa, and Latin America. 1 Larvae of the parasite in human bodies are capable to create cysts in all body organs, involving the liver in approximately 70% of cases, the lung in 25%, and other anatomic locations in 5%, such as the kidney, 2 the brain, 2 the heart and hip joints. 3 2% $ 4% of patients have kidney involvement while isolated kidney involvement (1.9%) is extremely rare. 4,5 It usually remains asymptomatic for many years.
The most common presenting signs and symptoms are abdominal mass, flank pain and dysuria. 6 Furthermore, they can masquerade as cystic renal tumors both clinically and radiologically.
Here, we present a case of isolated renal hydatid cyst (RHC) in a 40-year-old male which was misinterpreted as cystic renal cell carcinoma in Xinjiang. Based on radiological findings, we made a preliminary diagnosis of cystic renal cell carcinoma and planned exploration and cystectomy.

| Case presentation
After receiving symptomatic supportive treatments such as antiinflammatory and fluid rehydration, exploration was performed with the robotic assistance using the extraperitoneal approach. During the operation, it was found that the mass adhered to the lower edge of the liver and it was difficult to dissociate, so we decided to convert to open laparotomy. On exploration, a large cystic structure was found to arise from right kidney. To prevent intraoperative dissemination, hypertonic saline gauze was placed on the surrounding organs. Then, the cyst was opened, and daughter vesicles and membrane were removed ( Figure 2). Hydrogen peroxide and hypertonic sodium chloride were successively injected into the residual cavity as fungicides.
After partial resection of the capsule wall, the kidney was sutured and drainage was indwelled. There were no intraoperative or postoperative complications.
Histopathological examination revealed HC (Figure 3). The patient was on postoperative oral albendazole 10 mg/kg per day treatment for 1 year with regular follow-up, which has been uneventful.
1-month follow-up CT examination did not reveal any new or residual hydatidosis.

| DISCUSSION
HC is a common epidemic parasitic disease in pastoral areas around the world, which mostly occurs in people who have close contact with cattle, sheep, dogs, and other livestock. The overall disease burden of HC is significant, equivalent to the annual loss of more than 1 million disability-adjusted life years (DALYs). 7,8 RHC is caused by the invasion of fine-grained echinococcosis into the kidney, which often originates from the renal cortex and grows distensively. 9 Those without complications tend to have no conscious symptoms. With the enlargement of cyst and oppression of F I G U R E 1 Computed tomography scan of abdomen shows a large multiloculated cyst arising from right kidney, considering (multilocular cystic) renal carcinoma surrounding organs or tissues, soreness of waist and lumbago may occur in the late stage. Occasionally, cysts invade the renal calyces, and the white powdery cyst wall and daughter cysts are discharged with the urine, which can lead to renal colic or urine changes such as hematuria and pyuria. 10 The diagnosis of RHC should be combined with medical history, clinical manifestations and ultrasound, CT, and serological examinations. Ultrasound is the first choice among the auxiliary inspections.
The typical sonographic appearance is anechoic lesions with welldefined margins. 11 The "falling snowflakes" sign is characterized by multiple echogenic foci of hydatid sand, which is considered a pathognomonic finding for HC. 2 CT is more accurate than ultrasound, and the characteristic findings for RHC include a cyst with a thick or calcified wall, a unilocular cyst with a detached membrane, and a unilocular cyst with a detached membrane. 11 Laboratory tests include blood routine, intradermal allergic test (Casoni test) and indirect hemagglutination test and enzyme-linked immunosorbent assay, etc. Serologic and hemagglutination tests have low reliability but a positive test result is indicative of active disease. 12 RHC is difficult to differentiate by ultrasound and CT from simple renal cysts and cystic renal tumors in the early stage. The reasons for the initial misdiagnosis of this patient as a renal cystic tumor were as follows: (1) Since the incidence of RHC was low, the attending physician was not aware of it and took the history carelessly. (2) The