Ameroid Constrictor rings are used in the treatment of portosystemic shunts. Portosystemic shunts are vascular communications between the portal venous system and the systemic circulation. Portosystemic shunts divert portal blood away from the liver. Treatment of portosystemic shunts aims to attenuate the vessel and redirect portal venous blood to the liver. Ameroid Constrictor rings are used for the gradual attenuation of intrahepatic portosystemic shunts. Congenital portosystemic shunts can be completely or partially ligated with nonabsorbable sutures or gradually attenuated with an ameroid constrictor, cellophane band or hydraulic occluder. Gradual attenuation is the preferred method as this reduces the risk of postoperative complications. Ameroid constrictor rings consist of an inner ring of casein that is surrounded by a stainless steel sheath. Casein slowly absorbs body fluids and swells, reducing the ring’s internal diameter. This causes a fibrous tissue reaction which results in the gradual occlusion of the shunt in two or more weeks. The size of ameroid constrictor used depends on the shunt diameter. The perivascular fascia is dissected away from the shunt prior to placement of the ameroid constrictor. The ameroid constrictor is then slipped over the flattened vessel and the slot in the constrictor ring is obstructed with a key.
REFERENCES: 1. Berent, AC & Tobias, KM 2009, ‘Portosystemic vascular anomalies’, Veterinary Clinics of North America: Small Animal Practice, vol. 39, no. 3, pp. 513-541. [http://www.mdconsult.com]. 2. Mehl, ML, Kyles, A, Case, JB, Kass, PH, Zwingenberger, A & Gregory, CR 2005, ‘Surgical management of left-divisional intrahepatic portosystemic shunts: outcome after partial ligation of, or ameroid ring constrictor placement on, the left hepatic vein in twenty-eight dogs (1995–2005)’, Veterinary Surgery, vol.36, no. 1, pp 21-30. [http://ejscontent.ebsco.com].
