Small Ani. Sx- Portosystemic shunts

untimely's version from 2015-11-01 23:42

intro/ basics

Question Answer
what is a Portosystemicshunt (PSS)/ Portosystemicvascular anomaly (PSVA)?("in one word- a bypass") “... anomalous vessel(s) that allow normal portal blood to drain from the stomach, intestines, pancreas, and spleen and pass directly into the systemic circulation without first passing through the liver”
*Vessels of interest for a PSS? why do we care about these vessels?Many blood vessels from abd dump into the portal vein---> portal vein takes blood to the liver, where the liver filters and metabolizes things, then after that the blood drains into the hepatic veins which dump into caudal venacava. Then there is a renal vein, which goes from kidneys to Ca vena cava. The reason we care is because if we look between the renal vein and the hepatic vein, THERE SHOULD BE NO OTHER VESSELS ENTERING THE CA VENA CAVA BETWEEN THESE TWO VEINS (except for the little phrenicoabdominal veins which enter about 1cm cr to the renal vein.). Aside from that, NONE OTHER should be there. if there is, it is considered anomalous!!
there are many different types of shunting bypasses. Their names are descriptive of where they are coming from. what are the main shunts? (6)(A) Porto-caval shunt (from portal vein right to vena cava) (B) Porto-azygosshunt (C) Splacnic-cavalshunt (portal v. atresia) (D) Splenic-cavalshunt (E) Gastric-, mesenteric-or gastroduod–caval (F) Combination of any above.... AND ALSO Also… persistent ductusvenosus, microvascular dysplasia
what is a persistent ductus venosus?vestigial vessel that within a few days after birth closes..if persists, is the cause of a intra-hepatic portosystemic shunt (FYI:shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver.)
what is microvascular dysplasia?dogs present similar to portosystemic shunt, except shunt is not big- cant see or find it. can only dx histopathologically. It's a bunch of capillaries causing the problem.
Microvascular dysplasia is aka? how do animals get it? how do you fix it?Also referred to as portal vein hypoplasia. It is a Congenital problem (Shunting at microvascular level (portal hepatic capillaries)--> Not a diagnostically macroscopic shunt) They are Not amenable for surgery
what are the 3 ways to Classification of PSS?(1) where is it?= Intrahepatic (IHPSS) or Extrahepatic(EHPSS) (2) Congenital or acquired (EHPSS only) (3) Single or multiple
what is a Extrahepatic shunt? (EHPSS)(normal looks like a tree) the anomalous vessel is located outside the hepatic parenchyma (usually arise Ca to the level of T13 whereas the portal vein is around the level of L1)
what is a Intrahepatic shunt? (IHPSS)(normal looks like a tree) the anomalous vessel is located within the hepatic parenchyma (usually Cr to T13 whereas the portal vein is around the level of L1)
INTRAHEPATIC PSS vs EXTRAHEPATIC PSS--> WHO is more affected by each?INTRA: Medium to large breeds. EXTRA: Small breeds such as Yorkshire terrier, Miniature Schnauzer, Maltese, Havanese, Miniature Poodle
do CATS tend to get INTRA or EXTRAhepatic PSS more often?CATS are more likely to get EXTRAhepatic, but can get intrahepatic too (10%)
which type of PSS is Commonly assct’d with persistent ductus venosus?INTRAHEPATIC PSS
which type of PSS is the kind which happens in the "acquired shunt" circumstance?EXTRAhepatic
which is more common in general- intra or extrahepatic?extraheaptic
what are two reasons an animal can get an acquired EHPSS?(1) Chronic portal hypertension (2) Sequelae to acute or gradual congenital shunt attenuation
explain some situations where Chronic portal hypertension can lead to an acquired EHPSSportal vein hypoplasia (microvascular dysplasia), hepatic fibrosis (young animal), chronic hepatitis, cirrhosis, hepatic arteriovenous malformation
is an acquired shunt usually single or multiple?usually multiple
how do you tx Acquired Extrahepatic PSS?aimed at controlling HE (heaptic encephalopathy) and slowing progression of liver disease...* decision to treat surgically depends on number of acquired shunts (if 1-2 shunts, can sx fix, but if more prolly need to medically manage)
what is the hx like of a typical Congenital Portosystemic Shunt dog?Varied, but usu Failure to thrive, “runt”, Neurologic signs, Urinary complaints, *Unanticipated prolonged response to anesthetic Rx (take a long time to wake up)
why are there urinary complaints in a congenital portosystemic shunt dog?a lot of ammonium biurate crystals--> uroliths--> urainary complaints
why will the hepatic encephalopathy get worse after a meal high in protein?protein is broken down into ammonia, which the brain is already struggling with since the liver isnt breaking it down, so it makes the prob worse
*what is the Neurologic problem brought on by PSS? what are the signs of it?HEPATIC ENCEPHALOPATHY! Bizarre behaviour, Dementia, “Hysteria”, Aggression, Amaurosis, Deafness, Seizure & convulsions (Grand Mal in feline)
Gastrointestinal signs you see with a congenital PSS?Anorexia, Vomiting, Diarrhea, Pica, Polyphagia, Sialorrhea/ptyalism(cats)
what are some Other disorders/assocaited disorders in animals with PSS? (3)(1) Urinary lithiasis(dogs & cats -ammonium urate) (2) Cryptorchidism -dogs 50%, cats24 % (3) Prolonged anesthesia recovery (liver not metabolizing the drugs)
Presumptive diagnosis of congenital PSS based onAge, breed and C/S, Stunted growth, Biochemical abnormalities, Radiographic findings: microhepatica/ atrophy, renomegaly (bc uroliths)
what are some radiographic findings that might point to congenital PSS?microhepatica/ atrophy, renomegaly
what are the Biochemical abnormalities (+/-) you might see with a congenital PSS?Elevated hepatic enzymes, ***low BUN, Hypoglycemia, Hypoalbuminemia, Elevated pre-and post-prandial serum bile acid concentrations, Elevated blood NH4 concentration (BUN and albumin low, bile acids high)
how might the CBC appear with a congenital PSS?Mild, non-regenerative anemia, Microcytosis, target cell, poikilocytosis
Other potential diagnostic abnormalities assocaited with congenital PSS are.... (3)(1) Increased clotting time (bc impaired liver fxn) (2) Ammonium biurate rystalluria or urolithiasis (3) Protein C (enzyme which is a vit-K dependent enzyme...can use to see how they are responding to sx)
Portal-angiographic procedures (portography) can be used to DX PSS. what are different ways they can do this?cranial mesenteric arteriography, celiac arteriography, splenoportography, mesenteric portography. ....often use in conjunction with fluoroscopy to monitor distribution of dye though the liver.
what is CT angiography, how is it used to dx PSS?most commonly used dx tool. Use contrast media + CT (not U/S)
Ultrasonography is Most useful for the diagnosis of____shunts intrahepatic *Results largely dependent on operator experience :(
what is Nuclear scintigraphy, how can it be used in the dx of PSS?use Technetium99 (Tc 99m) an inject it through the spleen (spleen is most common route aka Transsplenicportal scintigraphy*, but can be Transcolonic(per rectum) but that requires a higher vol of Tm) Then see how long it takes for the tech. to get to the heart, and what happens along the way. In the shunt, it gets to the heart FASTER, and the liver doesn't really light up with the tech. Can id where shunt is, where it's going, and how many shunts there are
what are some things you can do to medically manage a PSS? (6)(1) Diet -low protein / highly digestible (2) Antibiotics +/-yogurt with active cultures (dec amount of ammonia producing bact in gut) (3) Lactulose (oral, retention enema) (4) Neutraceuticalsfor hepatic support (5) +/-Anticonvulsants (6) +/-Gastric protectant
Medical managment of PSS is recommended only in what 2 cases?(1) to stabilize before surgical correction (2) in cases in which surgery is not an option
what is prog like for PSS?50% are euthanized within 10 months after PSS Dx if only medically managed. Estimated survival (2 mo–2 yr)


Question Answer
what is the tx of choice for PSS?Surgical attenuation/ligation is treatment of choice!!
what are some of the sx options for tx of pss?**Ameroidconstrictor, **Cellophane band (**= most commonly used), Ligature (mainly intrahepatic shunts),Steel and Dacron®coil, Hydraulic occluder
why are ligatures not really in favor for fixing PSS now?cumbersome bc had to measure portal pressures during sx and see how tight you could tighten the ligature without having a spike in pressures-- if were to ligate it as if it were an ovarian pedicle, pt will prolly die. can't just tie off a shunt.
how do you go about sx to fix a PSS? (approach, etc-- general steps and things you should do)ventral midline (maybe sternotomy or paracostal if you need to), then ID the shunt (intraoperative localization) via mesenteric portography(requires fluoroscopy), transplenoportography, or Doppler ultrasonography. then, depending on how you try to close off the portal vein, might need to Monitor portal pressure (manometry) (jejunalor splenic vein catheterization). Then, always get a Liver biopsy* (esp if can't find shunt, bc need histo to look for microvascular dysplasia)
how would you describe what a shunt is like?Shunts are thin-walled vessels with turbulent blood flow
The portal vein caudal to the liver lies where?epiploic foramen (Borders= cd vena cava, portal v., liver, hepatic a.)
SX Step #1: Identify the shunt (approach? examine what vessels?)Ventral midline celiotomy. EXAMINE: (1) The vena cava -only the small phrenicoabdominal veins enter between the renal veins and the hepatic veins (2) The portal vein caudal to the liver lies in the epiploic foramen (Borders= cd vena cava, portal v., liver, hepatic a.) (3) The left gastric and splenic veins at the greater and lesser curvatures of the stomach\
If the shunt cannot be identified visually during sx, what do you do?a portography is arranged
how does the Ameroid constrictor work? which type of shunt is it usually used in?it is a ring of Hygroscopic compressed Casein which is clamped around the vessel. used MUCH MORE in extrahepatic shunts. The constrictor Gradually attenuates shunt in 4 -5 weeks--> due to swelling of the casein + induction of fibrosis, as well as tissue reaction.
what caution should you have with an ameroid constrictor?if over-dissect around vessel, metal ring flips and squishes vessel now it's attenuated completely
how does Cellophane banding work? which type of shunt does this work in?place cellophane band around vessel- dont need to tie it tight- can seal cellophane with a hemoclip- over a few weeks there is a FB reaction + fibrosis-->Causes gradual occlusion of veins by fibrosis. *Occlusion may not be complete. Can be used in IHPSS & EHPSS
Percutaneous Transjugular Coil Embolization (PTCE)-- how does this work? which shunts is it usually used in?used in IHPSS. insert coils inside shunted vessels- kinda dam up and slow flow, and then clots form, and then clot causes occlusion of shunt. Rapid occlusion (5-7 days), but May not incite complete shunt attenuation and has a higher cost
Hydraulic occluders are usually used with what kinda shunt? how does it work?IHPSS, Cuff secured subQ & gradually inflated every 2 weeks over 8 weeks
with PSS sx, Immediate postoperative period is critical!!!! what should you observe for, and how? (2)(1) Observe for signs of portal hypertension such as Abdominal pain and ileus, Hemorrhagic diarrhea, Metabolic acidosis, Endotoxemiaand cardiovascular collapse (2) Monitor for seizure activitySeizures that begin in post-operative period carry poor prognosis. Control with phenobarbital (cats); phenob, potassium bromide, levetiracetam(Keppra)
what is the risk of portal hypertension with an ameroid constrictor?minimal risk of severe portal hypertension unless weight of constrictor twists shunt. minimal dissection of shunt reduces risk. (New prototype for constrictor currently being developed at University of Florida --~5x lighter than current ameroidconstrictor)
what do you think if post-op you see ascites?Ascites is common postoperatively and is notan indication for removal of occluding device
post-op, you should monitor ammonia levels and Repeat liver function tests at about 60d postop. If liver function improved, what should you do?gradually wean off medical management one by one (in order)--> anti-seizure--> antibiotics--> lactulose--> low protein diet (Some animals must be maintained on low-protein / highly-digestible diet for life)
When is prog of PSS excellent? Fair? Guarded?Excellent with complete attenuation or ameroid constrictor attenuation. Fair to good with partial attenuation. Guarded with development of multiple extrahepatic shunts related to microvascular dysplasia in liver
Mortality rate varies with procedure... best to worst?ligation > ameroid≈ cellphone band
it is advised to do sx for PSS before what age?Advise to do surgery before 2 years of age
how does PSS present in CATS?Have neurologic signs similar to dogs but commonly have gastrointestinal signs as well. GI SIGNS: Anorexia, vomiting, diarrhea, pica, polyphagia, Sialorrhea/ptyalism. NEURO SIGNS: Grand mal seizure, aggression, excessive licking. Might also see Cardiac murmur. ALSO, high incidence of PSS in cats with copper-colored irises
how does lab/dx parameters differ for cats from dogs?ALB, ALT, ALP often normal in cats. Typically not anemic. Decreased BUN seen in only ~50% of cats with PSS. Ammonium biurateurolithsseen in 10% of cats (vs. 33% dogs)
how might improvement be different post-op for cats instead of dogs?Many cats have persistent neurologic signs post-operatively despite biochemical parameters & bile acids returning to normal post-operatively
what is prog of PSS like in cats?Prognosis with extrahepatic shunts not as good as in dogs

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