Microvascular dysplasia: clinical implications and confusion

摘要

Hepatoportal microvascular dysplasia (MVD) is a congenital and probably inherited microscopic disorder well defined in small breed dogs, usually having a Terrier heritage. In North America, MVD is most commonly encountered in Yorkshire Terriers where its occurrence places many dogs at risk for expensive and invasive procedures aimed at identifying a portosystemic vascular anomaly (PSVA). Kindreds of dogs of certain breeds with recognized members having PSVA, often have a high rate of MVD. In some breeds, as many as 85 percent of tested kindred (20 or more dogs) have had MVD based on bile acid testing. This finding and the very similiar histologic features between these disorders suggests a genetic relationship. Furthermore, failure of histologic lesions in many PSVA patients to fully resolve upon complete shunt ligation suggests that many of these dogs have coexistent MVD and PSVA. Since the historical, clinical, clinicopathological, and histologic features of PSVA have saturated the veterinary literature over the passed 20 years, many clinicians maintain a high index of suspicion for this relatively uncommon disorder when presented with a vaguely ill young dog with high serum bile acid values. MVD is easily mistaken for PSVA until the patient undergoes colorectal scintigraphy, portovenography, or surgical exploration, since liver biopsy does not reliably differentiate these two disorders. The existence of MVD explains why some dogs suspected of having PSVA on the basis of abnormal liver function and hepatic histology, lack macroscopic shunting vasculature on contrast radiologic study and surgical inspection. Thus, the problem remains: which patients should undergo evaluation for MVD and PSVA, considering the basic tenet of medicine: At firstdo no harm!