Page 751 - Clinical Small Animal Internal Medicine

66 Portosystemic Shunts and Microvascular Dysplasia 719

Anecdotal experiences suggest that older dogs and pugs patients may have normal serum biochemistry and a
VetBooks.ir may be at greater risk for seizures, but this has not been normal technetium scan in the face of continuing mild
elevations in serum bile acids. The significance of these
definitively proven. Cats seem at greater risk for neuro-
logic sequelae, including blindness and twitching, in
Protein C has been proposed as a useful monitoring tool
addition to seizures. Preoperative treatment with pheno- mild elevations to long‐term prognosis is not yet known.
barbitol and levetiracetam (Keppra®) has been shown to but the assay is not offered widely, and results from dif-
significantly reduce the incidence of seizures, although ferent laboratories may differ, making interpretation of
published reports and anecdotal experience suggest that single results difficult.
the risk is not completely abolished.
Nuclear Scintigraphy
Per rectal scintigraphy provides an estimate of shunt frac-
Therapeutic Decision Making
tion and is helpful in determining the degree of shunt clo-
In light of the fact that many patients have mild clinical sure following surgery. It does have some interobserver
signs, and surgical shunt attenuation has a significant variation, and we reported some dogs with normal tech-
morbidity/mortality rate, owners are sometimes faced netium scans following surgery that had persistent shunt-
with a difficult choice between long‐term medical man- ing through small tributary vessels. Therefore, the results
agement and surgical correction. Some dogs live appar- of scintigraphy should be interpreted in the context of
ently normal lives with no management at all, whereas other measures such as serum biochemistry and imaging.
others develop severe clinical signs within the first few Percutaneous transsplenic scintigraphy is more accurate
months of life. On risk–benefit analysis, a young puppy and may provide information about shunt anatomy in the
with obvious HE is more clearly a candidate for surgery hands of an experienced operator, but is more invasive
than an 8‐year‐old dog in which CPSS is detected on a and not yet performed routinely.
routine wellness check. An exception would be the older
male dog in which CPSS is diagnosed following urethral Abdominal Sonography
obstruction with ammonium urate calculi. Medical man- Assuming that the shunt was sonographically visible
agement in these patients may not control stone forma- before surgery, postoperative sonography is a mechanism
tion, and as urethral obstruction is, in itself, potentially for confirming closure of the shunt, increase in liver vol-
life‐threatening, many owners will opt for surgical ume, and decrease in kidney size. It is also useful for iden-
correction of the CPSS. Likewise, patients with severe tifying or monitoring development of urinary calculi.
polyuria/polydipsia may be generally happy but present
unacceptable management issues, making surgery an Computed Tomography
attractive option. Dual‐phase CT angiography is emerging as the most
Many dogs with severe clinical signs will become near‐ reliable way to evaluate patients postoperatively, allowing
normal on medical management, prompting the owners calculation of liver volume and perfusion, and evaluation
to question the necessity for surgery. The choice then is of shunt anatomy, presence of persistent shunting
between lifelong dietary management and other thera- through the original shunt or acquired vessels.
pies, weighed against a high probability for return of liver
function to normal following CPSS attenuation. Interpretation of Surgical Outcomes
Historically, patients have undergone minimal objective
follow‐up after surgical attenuation, making interpreta-
Ongoing Evaluation
tion of published outcomes difficult. Patients with
There are two main factors that should be considered persistently abnormal blood values may have persistent
when determining a patient’s progress, either with shunting, acquired shunts, PVH-MVD, or some other
medical or surgical management: liver function and the hepatopathy. Persistently abnormal technetium scans
presence and degree of portosystemic shunting. are now recognized to occur in a variety of scenarios,
including failure of the occlusion device to promote
Biochemical Evaluation complete occlusion, malpositioning of the occlusion
Liver function is usually monitored indirectly by meas- device, and development of acquired shunting. Clearly,
uring blood levels of the products of hepatic metabolism neither of these techniques is able to identify the etiology
including albumin, cholesterol and BUN . Return of cho- for the abnormal result, and thus inform the most appro-
lesterol and BUN to reference levels is a good indicator priate management plan.
that liver function is returning to normal. Serum bile Imaging using sonography may be helpful if the abnor-
acid levels are a sensitive indicator of macroscopic or mal vessel(s) are visible. The ideal strategy for evaluation
microscopic portosystemic shunting. Postoperatively, would include serial serum biochemistry including