Case 3 and 4
Both these two patients presented with irritative voiding symptoms. The CT findings are shown in figures 3 and 4 respectively. ELISA for Echinococcus antigen was positive in both the patients. The patients were initially treated with a four week course of albendazole. Both the patients underwent robot- assisted laparoscopic excision of the hydatid cyst (total pericystectomy) by author NPG. Ports were placed as for robotic radical prostatectomy. The cyst was closely adherent to the bladder anteriorly and the rectum posteriorly. The cyst was meticulously separated from surrounding structures and removed intact through a lower midline incision in the first case. In the second case a special trocar and cannula called the Palanivelu Hydatid System [PHS] was used to decompress the cyst. This was originally described in laparoscopic management of hydatid cysts of the liver  .This special instrument has a hollow trocar and two channels for suction which is very effective in evacuating the cyst contents and preventing spillage. The PHS was inserted via a small suprapubic incision and introduced into the cyst. After aspirating the cyst contents, 5% betadine wash was given inside the cyst and the opening in the cyst wall was approximated with 3-0 vicryl sutures. With the cyst decompressed further dissection proved to be much simpler and the hydatid cyst was dissected free from the rectum posteriorly. The specimen was entrapped in an endocatch bag and retrieved through the umbilical port. The postoperative period was uneventful and both the patients were discharged on the third postoperative day.
Figure 3. Images of case no. 3
A: USG pelvis showing multicystic lesion posterior to urinary bladder.
B: Contrast-enhanced CT showing the multicystic mass located in the rectovesical pouch pushing the posterior bladder wall anteriorly.
C: Cut open section of the specimen with multiple daughter cysts.
Figure 4 – Images of case no. 4
A: Contrast-enhanced CT abdomen and pelvis showing large pericyst containing multiple daughter cysts.
B: Port placement for robot assisted laparoscopic total pericystectomy. The PHS (Palanivelu Hydatid system) has been inserted through a suprapubic incision.
C: Palanivelu Hydatid system
D: Cut open hydatid cyst containing daughter cysts.
Figure 5 – Intraoperative images of case no. 4
A. Intraoperative view prior to commencement of dissection.
B. Palanivelu hydatid system inserted into the hydatid cyst.
C. All the cyst contents have been aspirated and the opening in the cyst wall is being closed.
D. Specimen entrapped in the endocatch bag is being removed through the umbilical port.
In view of its rarity, a hydatid cyst may not be the first differential diagnosis in a patient presenting with an isolated pelvic cyst. On imaging, a retrovesical hydatid cyst may mimic the following conditions: rectal duplication cyst, rectosigmoid neoplasm, posterior bladder diverticulum, cyst of the seminal vesicle, hydronephrosis in a pelvic kidney and large ectopic ureterocoele. All the four patients in our series were male patients. In female patients, however, a retrovesical hydatid cyst may mimic any one of the following gynaecological conditions: ovarian neoplasm, Mullerian remnant, hydrosalpinx, pseudomyxoma peritonei, and tubal pregnancy. Though the presence of daughter cysts on CT is pathognomonic, in some cases the final diagnosis may be made only after surgery.
None of the patients in our case series had hydatid cyst located elsewhere in the abdominal cavity. The possible pathogenesis of isolated retrovesical hydatid cyst is that a small primary focus in the liver may rupture and seed its contents into the pelvis and then the primary focus may undergo spontaneous resolution. .
Retrovesical hydatid cysts may have varied and non specific presentation. In the series by Angulo et al , the most common presentation was a palpable mass followed by flank pain, frequency, urinary retention and pain on micturition. Patients may also present with constipation, weight loss and renal insufficiency. Whyman et al have described a case of retrovesical hydatid cyst presenting with hematospermia and obstructive azoospermia . Dogra et al reported a case of retrovesical hydatid cyst presenting with acute urinary retention. In this patient a small calcified cyst was also noticed in the left lobe of liver. Open total pericystectomy was done along with excision of the liver cyst. 
The goal of surgical management is total cyst excision (total pericystectomy) without spillage and contamination of the field. Location within the narrow confines of the pelvis along with dense adhesions to surrounding structures may render dissection a formidable task. Partial pericystectomy may have to be resorted to in situations where separation from neighbouring structures is not possible. Most of the cases reported in literature have been managed by open total or partial pericystectomy.[4,5] In the series by Angulo et al , open total pericystectomy was performed in 22 patients while another 20 patients underwent partial cyst excision. In four patients in whom the hydatid cyst had infiltrated or was closely adherent to the bladder wall, cyst excision was accompanied by partial cystectomy. Ureteric reimplantation was required in three cases. Ali Horchani et al  reported a series of 27 cases of retrovesical hydatid cyst. Nine patients underwent open total cystectomy, while in 17 cases open partial pericystectomy was done. Two patients had ureteric reimplantation and four patients had closure of cystovesical fistulas. Postoperatively one patient died with septic shock and one was re-operated for peritonitis. Mean postoperative hospital stay was eight days. These two series highlight the difficulties faced in open surgical management of these technically challenging cases. Kumar et al. described two cases of retrovesical hydatid cysts which were managed laparoscopically with laparoscopic cyst aspiration, instillation and suction .
This is the first reported use of the da Vinci surgical system for the management of retrovesical hydatid cyst. Enhanced magnification, 3-D vision and endowrist technology ensure accurate dissection with no collateral damage. Furthermore use of the Palanivelu Hydatid System allows safe decompression of the cyst without any spillage.
Hydatid cyst should be one of the differential diagnoses in patients presenting with isolated retrovesical cysts, as appropriate prophylactic measures need to be taken intra-operatively to prevent spillage. Such patients present with nonspecific lower urinary tract symptoms. Robot assisted laparoscopic surgery provides a safe and feasible option in the management of hydatid cysts located in the pelvis.
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Date added to bjui.org: 15/09/2010
DOI: 10.1002/BJUIw-2010-019 –web