Page 606 - Small Animal Internal Medicine, 6th Edition

578 PART IV Hepatobiliary and Exocrine Pancreatic Disorders

has been reported in a young cat but is very rare (McConnell with an intrahepatic PSS were Siamese (Lipscomb et al.,
et al., 2006). 2007). Most cases present before 2 years of age; many are
VetBooks.ir even these are recognized less commonly than in dogs. Con- younger than 1 year, but old cats with congenital PSSs are
Most cases of PSS in cats are therefore congenital, but
frequently recognized.
The typical clinical signs in cats with congenital PSS are
genital PSSs are usually single or, at most, double vessels
and may be intrahepatic or extrahepatic (Lipscomb et al., gastrointestinal, urinary, or neurologic (HE), although the
2007). Extrahepatic PSSs represent abnormal communi- latter tend to predominate in cats and, anecdotally, are often
cations between the portal vein or one of its contributors more severe than in dogs. Cats typically present with a
(e.g., left gastric, splenic, cranial, or caudal mesenteric or history of waxing and waning neurologic signs consistent
gastroduodenal vein) and the caudal vena cava or azygos with HE rather than a sudden acute HE crisis. The typical
vein. Intrahepatic PSSs may be left-sided, in which case signs of HE are outlined in Box 33.3. Hypersalivation is a
they are believed to represent a persistence of the fetal common sign of HE in cats but is rare in dogs. There is
ductus venosus after birth (patent ductus venosus [PDV]; sometimes an association between signs of HE and feeding,
White et al., 2001), or they may be right-sided or centrally which may relate to glutamine metabolism by enterocytes
located in the liver, in which case they are believed to be releasing ammonia; however, not all cats display these signs.
anomalous vessels. Cats in acute crisis may present comatose or with seizures;
The pathophysiology of congenital PSS largely relates cats appear to be more susceptible to seizures than dogs,
to the shunting of unfiltered blood directly into the sys- preoperatively and postoperatively. The reason for this is
temic circulation, resulting in hyperammonemia and HE. unknown, although it has been suggested that sudden
The pathophysiology of HE is outlined in Chapter 33. changes in the concentrations of ammonia and other metab-
The shunting vessel acts as a low-resistance pathway for olites in the blood after surgery or sudden changes in medical
some of the portal blood, bypassing the higher resistance management may destabilize neurotransmitters in cats more
intrahepatic portal vasculature. Portal pressure is therefore than dogs. Drug intolerance is common, particularly pro-
lower than normal in cats with congenital PSS, which is longed recovery from routine anesthesia for spaying or neu-
an important distinguishing feature from (rare) cases of tering. Animals with PSS may also show intermittent
acquired shunting, in which there is portal hypertension vomiting and/or diarrhea. Urinary tract signs are caused by
and therefore increased portal pressure. Concurrent hepatic cystitis associated with urate calculi and polyuria or polydip-
microvascular dysplasia or portal vein hypoplasia, which sia, but they are less common in cats than in dogs. It is
can confuse this differentiation, occurs in some dogs (see important to note that as opposed to dogs, many cats with
Chapter 36) but has only been reported in one cat (Sugi- urate stones in the bladder do not have a PSS. In one study
moto et al., 2018). Shunting may also allow bacteremia and from a large U.S. stone center, only 7 of 159 cats with urate
potentially infections of hematogenous origin that may stones had a diagnosis of a congenital PSS (Dear et al., 2011).
present as so-called pyrexia of unknown origin, although Cats with congenital PSS also often show signs of poor
this is rare. Additional effects of portal blood bypassing growth compared with their litter mates (Fig. 35.10). There
the liver are hepatic atrophy and a reduction in the meta- has been a reported high prevalence of copper-colored irises
bolic activity of the liver, which contributes to inefficient
use of dietary components, poor growth, and loss of lean
body mass.
Liver atrophy (microhepatia) and changes in hepatic
organelle function are partly caused by changes in hepatic
perfusion. The portal blood usually provides about 50% of
the liver’s oxygen requirement, but this is obviously reduced
in cats with PSS. Cats with PSS typically have arteriolar
hyperplasia in an attempt to compensate for the reduced
portal flow, but they often still have some degree of hepatic
underperfusion. In addition, PSS results in reduced delivery
of hepatotrophic factors, such as insulin, to the liver, which
further contributes to hepatic atrophy.
Clinical Features
Persian and Himalayan cats were reported to be at increased
risk for congenital PSS in a small case series, and another
series noted that purebred cats in general were overrepre- FIG 35.10
sented; however, cats of any breed, including mixed-breed A 6-month-old kitten with a congenital portosystemic shunt,
cats, can be affected. Both sexes appear to be equally at risk. demonstrating very small size for its age and also copper-
There is no reported association between breed and shunt colored irises, which are often noted in kittens with
types (unlike in dogs), although in one study 6 of 13 cats portosystemic shunts.