Page 638 - Small Animal Internal Medicine, 6th Edition

610 PART IV Hepatobiliary and Exocrine Pancreatic Disorders

Primary Hypoplasia of the addition, some dogs may have both congenital PSS and
Portal Vein, Microvascular Dysplasia, and MVD or portal vein hypoplasia, further confusing the diag-
Noncirrhotic Portal Hypertension
VetBooks.ir Etiology and Pathogenesis nosis. Cairn Terriers and Yorkshire Terriers in particular
have been reported with MVD. In one breed (Cairn Terrier),

terminal portal veins. In this breed it is believed to be an
There have been several reports of vascular disorders in the site of anatomic abnormality has been identified as the
young dogs associated with portal hypertension, usually autosomal inherited trait, but the specific mode of inheri-
ascites, and characteristic histopathologic changes in the tance has not been established. Typical signs include vomit-
liver, including a reduction in smaller portal vein branches, ing, diarrhea, and signs of HE, although the clinical signs,
increased numbers of arterioles, and a variable amount of particularly the HE, are notably milder in dogs with MVD
mild fibrosis. There are some reports of overt hypoplasia of than in those with congenital PSS unless both disorders
the extrahepatic portal vein, but most studies of noncirrhotic occur concurrently. Dogs with only MVD are somewhat
portal hypertension and MVD appear to describe portal vein older, and many have mild to no signs of illness. In the case
hypoplasia confined to the intrahepatic vasculature. These of young purebred dogs that have been screened for con-
diseases may all be different abnormalities or may represent genital PSS before sale or that are ill for nonhepatic reasons,
different spectra of the same abnormalities, but their clinical a high SBA concentration may be the only finding.
presentation, treatment, and prognosis are similar. A lack of
intrahepatic or extrahepatic portal vein branches results in Diagnosis
portal hypertension, with the same potential consequences The diagnosis of MVD or intrahepatic portal vein hypoplasia
as those of chronic hepatitis (see earlier), including ascites, and noncirrhotic portal hypertension relies ultimately on
gut wall edema, and often GI ulceration and acquired PSSs liver biopsy findings of intrahepatic portal vein hypoplasia
(Fig. 36.13). Dogs with MVD often do not present with in the absence of a grossly demonstrable shunting vessel. The
notable portal hypertension; despite this, MVD has been liver biopsy findings alone can be indistinguishable from the
grouped with these diseases by the World Small Animal changes that occur secondary to congenital PSSs, so the clini-
Veterinary Association (WSAVA) Liver Standardization cal findings of concurrent portal hypertension and ruling out
Group (Cullen et al., 2006). Dogs reported with MVD typi- a shunting vessel are important parts of the final diagnosis.
cally have shunting at the level of the hepatic lobule but no Clinicopathologic findings are similar to those in dogs with
clinical signs of overt portal hypertension. congenital PSS and include evidence of hepatic dysfunction
Any breed can be affected, but MVD particularly affects (e.g., hypoalbuminemia) and hyposthenuria.
small-breed dogs; Yorkshire Terriers and Cairn Terriers Microcytosis is much less common with MVD than with
show a particularly high prevalence, whereas noncirrhotic congenital PSS. One study suggested that having a normal
portal hypertension often affects large-breed dogs. protein C concentration (>70% activity) had a high sensitiv-
ity and specificity for differentiating MVD from a congenital
Clinical Signs PSS, in which the protein C concentration is usually low
Dogs with all these conditions typically present at a young (Toulza et al., 2006). Microhepatia and hypoechogenic
age with a combination of signs of portal hypertension and abdominal fluid are the notable abdominal ultrasonographic
PSS, the severity of which depends on that of their lesions. findings in dogs with noncirrhotic portal hypertension; it
Because of the acquired PSS seen in these patients, some of may be possible to visualize multiple acquired PSSs ultraso-
the clinical signs and clinicopathologic findings overlap with nographically. Dogs with MVD alone tend not to have ascites
those of congenital PSS, particularly because all these dis- and have less marked increases in SBA concentrations than
orders typically present in young dogs. Therefore the pres- dogs with a true congenital PSS.
ence of other signs of portal hypertension (e.g., ascites) is The most important aspects of identifying a dog with
an important clinical clue that one of these disorders with MVD, portal vein hypoplasia, and/or noncirrhotic portal
acquired PSS may be present, rather than a congenital PSS. hypertension are ruling out a surgically correctable PSS,
Dogs with portal vein hypoplasia or idiopathic noncir- identifying portal hypertension (which requires treatment;
rhotic portal hypertension typically present between 1 and 4 see earlier), and obtaining a liver biopsy for confirmation
years of age and are often purebreds of either gender; large or exclusion of other hepatopathies. Portal vein hypoplasia
breeds predominate. Early reports of congenital or juvenile is similar clinically, on clinical pathology, and on diagnostic
hepatic fibrosis in German Shepherd Dogs may also have imaging to end-stage chronic hepatitis with cirrhosis; the
represented a form of noncirrhotic portal hypertension. Pre- only way to differentiate the two is on liver histology. In
senting signs are typically those of portal hypertension, with general, portal vein hypoplasia–noncirrhotic portal hyper-
abdominal distention associated with effusion, GI signs, tension carries a much better long-term prognosis than cir-
polydipsia, weight loss, and, less consistently, signs of HE. rhosis, so the differentiation is important prognostically.
Dogs are often surprisingly alert (Fig. 36.14).
Dogs with MVD present with similar clinicopathologic Treatment and Prognosis
findings but usually without overt evidence of portal hyper- The prognosis for all these conditions appears to be relatively
tension or ascites. MVD tends to affect terriers and thus good, provided that the clinical signs can be controlled. They
overlaps with breeds at high risk for congenital PSSs. In are nonprogressive, and there is no surgical treatment for any