Research Update: The efficacy of ameroid ring constrictors for treating portosystemic shunts

In this retrospective study from two university teaching hospitals, the medical records of 168 dogs with a single portosystemic shunt treated with an ameroid ring constrictor were reviewed to evaluate morbidity and mortality. An ameroid ring constrictor is placed around a portosystemic shunt, and the vessel is gradually occluded when the ameroid (a hygroscopic compressed casein that expands in fluid) expands within its stainless steel cylinder, fibrous tissue develops in response to the constrictor, and thrombosis occurs.

The median follow-up period in this study was three years. The dogs' median age at diagnosis was 12 months and median body weight was 8.6 lb (3.9 kg). Thirty-one percent of the dogs were Yorkshire terriers. Of the 162 dogs in which the location of the shunt was recorded, 104 dogs (64%) had a portacaval shunt and 58 dogs (36%) had a portoazygous shunt.

Postoperative complications (e.g. seizures, abdominal distention, hemoperitoneum, prolonged clotting) developed in 17 dogs (10%), and the morality rate was 7.1% (four of the 12 dogs that died had no complications). Ninety-four percent of the dogs had an excellent or good outcome after surgery. Of the 86 dogs with excellent outcomes, 81 were normal without any medical treatment or a special diet. In dogs evaluated with scintigraphy six to 10 weeks after surgery, 21% had evidence of persistent shunting.

Predictive factors for excellent clinical outcome included a high preoperative albumin concentration, a low preoperative leukocytosis, low portal pressure after occlusion, and the absence of postoperative seizures and shunting. Although limited by the study's retrospective nature, the authors concluded that ameroid ring constrictors provided favorable results for dogs with a single portosystemic shunt.

Mehl ML, Kyles AE, Hardie EM, et al. Evaluation of ameroid ring constrictors for treatment for single extrahepatic portosystemic shunts in dogs: 168 cases (1995-2001). J Am Vet Med Assoc 2005;226:2020-2030.

COMMENTARY

Hepatic encephalopathy secondary to a single portosystemic shunt is a common clinical problem in small-breed dogs. The clinical signs can be life-threatening and are related to hepatic dysfunction, such as gastrointestinal disturbances and central nervous system derangements. While medical treatment can ameliorate acute presentations, surgical occlusion of the shunt is recommended for a better long-term prognosis.

Gradual occlusion of a portosystemic shunt, as with the ameroid ring constrictor, may allow the hepatic architecture to develop in response to the increased vascular supply and prevent fatal portal hypertension, as can occur with rapid occlusion of the shunt. In this multihospital study, the authors extensively document numerous preoperative and postoperative patient characteristics related to morbidity and mortality and clinical outcomes. It will be interesting to note if future morbidity and mortality rates will be reduced as clinicians identify and treat predictive factors as outlined by these authors.

The information in "Research Updates" was provided by Veterinary Medicine Editorial Advisory Board member Joseph Harari, MS, DVM, DACVS, Veterinary Surgical Specialists, 21 E. Mission Ave., Spokane, WA 99202.

Joseph Harari, MS, DVM, DACVS