[Subperitoneal cyst in a Friesian mare].

The case of a 5-year-old Friesian mare with a mass in her abdomen and a gait irregularity of the left hind limb is discussed. At rectal ultrasonogrphic examination the mass appeared to be a thin-walled, anechogenic cavity in the left abdomen. By means of laparoscopy the mass could be visualized as a smooth structure, covered by peritoneum and fat. Under laparoscopic guidance the mass was punctured and fluid was aspirated. Cytological and bacteriological findings of the fluid were indicative of a cyst. After drainage of the cyst the locomotion disorder of the left hind limb disappeared. It is concluded that this horse suffered from a subperitoneal cyst, a rare disorder in humans and never previously described in horses. The case emphasizes the value of laparoscopy in the diagnosis and treatment of (intra)abdominal masses and further clearly shows that in the differential diagnosis of locomotion disorders not only structures related to the locomotion system should be taken into account.