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Table 1 Documented porto-systemic shunts in foals

From: Computed tomography angiography of a congenital extrahepatic splenocaval shunt in a foal

  Clinical signs Laboratory values Imaging findings Treatment Outcome Ref.
Belgian, male age 5 weeks Episodic disorientation, recumbency, thrashing, nonresponsive to external auditory stimuli, apparently blind and would throw his head and lunge violently Blood ammonia 380/40 μmol/L (sample/control) Total bile acids 86 μmol/L (< 20) Total bilirubin 12.0 mg/dL (0.3–3.5) γGT 21 U/L (10–59) BUN 42 mg/dL (10–27) Ultrasound: large vessel appeared to communicate with the caudal vena cava Positive contrast portography: intrahepatic portocaval shunt outlined by contrast agent flowing from the portal vein to the caudal vena cava without parenchymal perfusion Surgery: shunt ligated with 2 polypropylene Shunt ligation loosened within 16 days Attempts to relegate led to uncontrollable hemorrhages Euthanasia was performed [5]
Belgian, female age 5 months Small for her breed and age, clumsiness, acute blindness, head pressing, circling, staggering, circling, dragging all four feet, no proprioceptive deficits, apparently blind Blood ammonia 179/21 μmol/L (sample/control) Total bile acids 83 μmol/L (< 20) Total bilirubin 1.7 mg/dL (0.3–3.5) γGT 29 U/L (10–59) BUN 11 mg/dL (10–27) Positive contrast portography: large portocaval shunt delineated by contrast agent. No filling of portal veins within the liver was observed Surgery: shunt ligated with double ligatures of 5 polyester suture material Clinical improvement. Persistent increased blood ammonia (100 μmol/L) and serum bile acids (24 μmol/L) The foal remained healthy, without recurrence of clinical signs 2 years after ligation, but stayed small for her breed [5]
Mixed breed Arab, female age 9 weeks Intermittent episodes of circling, incoordination, absence of menace reflex, apparent blindness, inability to nurse, lethargy, unresponsiveness, ptyalism, bruxism, mild apathy, circling, ataxia, hypermetric gait of the forelimbs, and high head carriage Blood ammonia 208 μmol/L (< 50) Total bilirubin 4.8 mg/dL (0.5–2.3) Ultrasound: no shunt vessel identified CT angiography: an abnormal vessel originated from the intrahepatic portion of the portal vein, entering the most ventral aspect of the caudal vena cava immediately caudal to the diaphragm Echocardiography with transsplenic injection of agitated saline: immediate after injection contrast in the right atrium and ventricle Intra-operative ultrasound: Intrahepatic portocaval shunt identified 2 cm inside the liver parenchyma, running parallel and in contact with the caudal vena cava and entering the most ventral aspect of the caudal vena cava, immediately caudal to the diaphragm Surgery: shunt ligated with cellophane Clinical improvement within 2 days Blood ammonia still slightly increased 6 weeks after surgery (54 μmol/L), bile acid normal (5 μmol/L) After 7 months: foal is bright and alert [4]
American miniature, female age 5 weeks Hypersalivation, trismus, poor appetite, hyperaesthesia, aimless wandering and blindness Developed generalized pruritus, head pressing, marked ataxia, hindlimb stiffness, hypermetria, ataxia in all 4 limbs, disorientation, walking into stationary objects, difficulties locating the dam, no menace reflex and the pupillary light reflex absent bilaterally Blood ammonia 92.0 μmol/L (7.6–63.2 μmol/L) Bile acid 54.6 μmol/L (< 15 μmol/L) γGT 86 iu/l (slightly elevated) Creatinine 53 μmol/L (decreased) BUN 1.8 mmol/L (decreased) Ultrasound: liver reduced in size, hepatic portal vein and caudal vena cava were identified. An abnormal vessel arised from the prehepatic portal vein, which looped dorsally and caudally to merge with the caudal vena cava near the right renal vein Intra-operative mesenteric portovenography: a single extrahepatic PSS was identified curving dorsally into the caudal vena cava Cranial to the origin of the shunt, the portal vein was markedly reduced in diameter Surgery: shunt ligated with 4 metric silk Clinical improvement. The foal had grown to normal size and had shown no clinical disease At 3 years of age subjected to euthanasia due to severe abdominal pain. Post mortem examination was not performed [3]
Dutch Warmblood, male age 2 months Episodes of apathy and ataxia, gnashing, circling, apparent blindness, depression, hypermetria alternated with dysmetria of all 4 limbs, bilateral horizontal nystagmus, ptosis, variable menace reflex and delayed correction reflexes Blood ammonia 117 µmol/L (11–55) Bile acid 53 μmol/L (1–8.6) Unconjugated bilirubin 168 μmol/L (< 35) CT angiography: abnormal vessel identified, looping from the portal vein to the caudal vena cava at the region. The abnormal vessel looped to the left and caudally, entering the left side of the caudal vena cava, just cranial to the left renal vein. The total length of the shunting vessel was approximately 5 cm. Cranial to the shunt, a well-developed portal vein continued, the gastroduodenal vein joined the portal vein and the vein branched into the liver Surgery: cellophane ligation was planned. Surgery aborted due to complications Euthanasia