Hydatid cyst is a parasitic infestation. It most commonly involves the liver, followed by the lungs. The kidney is rarely involved. Characteristically, it presents as a multiloculated cyst with daughter cyst(s) on imaging. We present a case diagnosed as simple renal cyst found to be a hydatid cyst on exploration. A 50-year-old woman presented with right flank pain without hematuria or lower urinary tract symptoms (LUTS) for 6 months duration. On ultrasonography, a 6 cm × 7 cm simple cyst at the parapelvic location with hydronephrosis was found. Contrast-enhanced computed tomography kidney, uterus, bladder (CECT KUB) showed a large noncommunicating cyst of dimension 79.3 mm × 63.6 mm × 62.8 mm with a thin smooth wall compressing the pelvis, causing hydronephrosis. On exploration, a daughter cyst within the hydatid cyst was found. All of the fluid was drained, and then the ectocyst was removed. There was no communication between the cysts and the pelvicalyceal system.
Keywords: Hydatid cyst, imaging, renal, simple renal cyst
Hydatid cyst is a zoonotic disease. The larval stage enters in humans, goes through the portal system into the liver, and forms a cyst. The kidney is involved in 2% of the cases. Most of the cases are asymptomatic, diagnosed on imaging. On imaging, a multiloculated cyst with daughter cyst(s) is diagnostic but unilocular cyst with a detached membrane is also suggestive of a hydatid cyst.  In cases with noncharacteristic cystic lesion, the kidney may pose a diagnostic dilemma; double contour thick wall on ultrasonography or the presence of hydatid cyst in other organs favors the diagnosis. 
Herein is a case report of a renal hydatid cyst, presented as a simple renal cyst on imaging.
A 50-year-old woman presented with right flank pain for a duration of 6 months without history of hematuria or lower urinary tract symptoms (LUTS). She had no history of nausea, vomiting, or weight loss. There was no history of contact with dogs or other animals. Her appetite and bowel habit were normal.
On examination, she was found to be of normal build and nutrition. Her renal angle was normal but mild tenderness was present on palpation. There was no organomegaly.
Her complete blood count and biochemical blood investigation were normal, except raised eosinophil count.
On ultrasonogarphy, a 6 cm × 7 cm simple renal cyst at the parapelvic location causing hydronephrosis was detected [Figure 1]a. Contrast-enhanced computed tomography kidney, uterus, bladder (CECT KUB) showed a large cyst (79.3 mm × 63.6 mm × 62.8 mm) with a thin smooth wall in the right kidney compressing the renal pelvis, causing hydronephrosis. Cyst fluid did not show any contrast enhancement [Figure 1]b.
The clinical features with physical examination, along with investigations, suggested a simple renal cyst. Decompression and marsupialization of the cyst were planned.
On exploration, a large cyst was found extending from the hilum to the lower pole, causing hydronephrosis. On opening the cyst, daughter cysts were found. Taking precaution, the cyst fluid was drained, along with all the daughter cysts and the hydatid sands [Figure 2]. Then, the ectocyst was dissected from the renal parenchyma. Communication with the pelvicalyceal system was checked by the administration of methylene blue (HIMEDIA, S022-125ML) through preoperatively placed ureteric catheter.
In the postoperative period, the patient recovered well. She was treated with albendazole. Following treatment, there was complete resolution of eosinophilia and she became free of symptoms.
The term “hydatid” came from the Greek word “hudatis,” meaning watery vesicle. Cystic form of the Echinococcus larval stage has been well-recognized since ancient times. Rudolphi, in 1808, first used the term hydatid cyst to describe Echinococcus in humans.  Hydatid disease is endemic in Mediterranean countries, the Middle East, South America, China, and India. Dogs act as definitive hosts, whereas cattle are the intermediate hosts. Humans are accidentally infected by the larva. The most common organ involved is the liver (in 75% of cases) followed by the lungs (in 15% of cases). The kidney is rarely involved. Symptomatic patients usually present with flank pain and benign renal mass, and rarely with hematuria and hydatiduria. But most of them are asymptomatic and diagnosed on imaging. Hydatid cyst is very slow-growing, but if untreated, it may rupture and can cause anaphylactic reaction. Also, it can disseminate and spread to multiple organs, which can pose great challenge in its eradication. Diagnosis of hydatid cyst is usually based on the patient’s history and imaging, and it should be confirmed by serological test.  Currently, hydatid arc 5 antigens in double-diffusion test is the most sensitive and specific test. Ultrasonography and CT are the most common imaging modality used to diagnose renal hydatid cyst. Gharbi et al. first classified the hydatid cyst based on ultrasonography.  Multiloculated cyst, daughter cyst, floating membrane, “falling snowflakes sign,” spiral sign, and ring-like calcifications are all diagnostic of hydatid cyst in ultrasonography. ,, Similarly, on CT scan, unilocular cyst with a detached membrane, multiloculated cyst, daughter cysts, and a cyst with a thick or calcified wall are suggestive of hydatid cyst. 
Surgery is the mainstay of management. Treatment with mebendazol or albendazole helps to prevent seeding. A variety of surgical options, ranging from marsupialization and pericystectomy to nephrectomy, are advocated. Laparocopic aspiration of the renal hydatid cyst has also been reported.
Hydatid cyst can also present on imaging as simple renal cyst with thin wall with anechoic space, as seen in our case. However, simple renal cyst accounts for more than 70% of the asymptomatic benign renal mass. So, it is difficult to diagnose hydatid cyst unless a high degree of suspicion exists. Cysts involving other organs, particularly the liver, can also be a clue. As renal cyst is the most common finding on imaging; it is not uncommon to miss hydatid cyst unless serological test becomes routine in all cases of renal cyst.
We concluded that the early stage of renal hydatid cyst may present as simple renal cyst. Serological test should be done in all the cases, particularly in patients of endemic areas, with positive history of animal contact or cysts involving other organs.
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]