The retrovesical location of the hydatic cyst is rare. To our knowledge, we report the first case of retrovesical hydatic cyst with spontanoeus fistulisation in the rectum in a 70 year old patient who presented with acute urinary retention.

A 70-year-old man presented with a history of Atrioventricular block 1st degree. He reported a 4 month history of dysuria, pollakiuria and episodes of fever peaks without hydaturia complicated by a acute urinary retention . The physical examination Shows a mobile hypogastric mass, blood test (including eosinophils) is normal. A pelvic and abdominal ultrasound (Figure 1) showed a retrovesical mass honeycomb shape measuring 18,5 cm in height In favor of a hydatic cyst without hepatic localization.

The abdominal computed tomography (CT) scan (Figure 2) showed a 12.5×13×10 cm calcified cystic lesion between the rectum and the bladder exerting a mechanical effect on the upper urinary tract causing a bilateral pelvicalyceal dilation. Serology (indirect haemagglutination) was positive with a titre 1/3200.

The evolution was marked by the emission of daughter vesicles in the stools explaining the appearance of a spontaneous fistula between the retrovesical hydatid cyst and the rectum. On digital rectal examination does not find a fistulous path with a small soft prostate. The patient had a rapid spontaneous resolution of symptoms. Contrast computed tomography (Figure 3) confirmed the absence of a retrovesical hydatic cyst. Retrovesical hydatidosis is a rare condition (0.1–0.5%) [1].

To our knowledge, this is the first report of a retrovesical hydatic cyst Fistulized in the rectum. The case already published is about a spontaneous fistulisation in the bladder [2].