IMAGING DIAGNOSIS—COMPLEX INTRAHEPATIC PORTOSYSTEMIC SHUNT IN A DOG MARC-ANDRE´ D’ANJOU, LOUIS HUNEAULT
An unusual form of congenital intrahepatic portosystemic shunt was identified in a 3 12-month-old female Labrador Retriever with neurologic signs. Ultrasonography and contrast-enhanced computed tomography were used to characterize the shunt morphology. An unusual, looping right-divisional shunt connected back to the portal vein that formed an ampula in the right-central portion of the liver. An irregularly shaped window-like opening connected the combined right-divisional loop and aneurysmal portal vein, and the caudal vena cava, while this vascular pool gradually fused more cranially. Imaging features of this complex vascular anomaly, which has not been previously reported, are presented. Veterinary Radiology & Ultrasound, Vol. 49, No. 1, 2008, pp 51–55.
Key words: dog, intrahepatic, portosystemic, shunt.
History and Clinical Findings
A
right dorsolateral wall of the more central portal vein, which was focally dilated, connecting this other segment of the portal vein directly to the caudal vena cava (Fig. 1D). This finding indicated an irregular window-like opening that joined an aneurysmal portion of the portal vein to the caudal vena cava as well as to the distal extent of the right-sided looping vessel. Furthermore, another opening connecting the right-sided loop and the aneurysmal portal vein was identified. Turbulent flow connections were confirmed with color Doppler at the confluence of the looping right-divisional shunt, the dilated portion of the portal vein, and the caudal vena cava. The caudal vena cava became larger at the level of the vascular connections. The origin of the left portal branch and other right-sided hepatic veins was not identified. The hepatic artery was enlarged (4 mm). The kidneys were enlarged (7.9 cm in length on the left and 8.27 cm on the right; kidney-to-aorta ratio of 11.3 and 11.8, respectively2) and cortices were hyperechoic in comparison with the liver (Fig. 1B). Mineral sediment and small (1–2 mm) calculi were present in the bladder. There was no evidence of peritoneal effusion. To better characterize this complex intrahepatic shunt, computed tomography (CT)-angiography was performed as previously described,3,4 using a dosage of 2 ml/kg of iopamidol at 5 ml/s. A 10 ml test bolus was used to determine the time delay for maximal enhancement of the portal vein (30 s postinjection). Pre- and postcontrast transverse images of the abdomen (diaphragm to L4) were acquired helicoidallyw and reconstructed with a
3 12-MONTH-OLD,
10 kg, intact female Labrador Retriever had episodic ataxia, unconsciousness, and chronic coughing. The dog was cachexic and lethargic, but responsive to stimuli. There was hyperthermia (39.91C), tachycardia (148), tachypnea (100), moderate neutrophilia (24.6 109/l), reduced blood urea nitrogen (1.51 mmol/l), elevated alanine aminotransferase (132 U/l) and alkaline phosphatase (227 U/l) levels, hypoproteinemia (34.6 g/l), and hematuria (4 þ ) and proteinuria (1 þ ). Microhepatica was suspected from thoracic radiographs. Bile acids were elevated (pre: 49 mmol/l [normal range: 0–6]; post: 148 mmol/l [normal range: 0–15]).
Imaging Sonographically, there was a small liver with reduced visibility of the intrahepatic portal veins and a large gallbladder. The portal vein was normal in size,1 but had an irregular portal flow with increased velocity (up to 45 cm/s) (Fig. 1A). From subcostal and right-sided intercostal windows, a long, anomalous vessel 1.1 cm wide was found involving the right portal branch (Fig. 1B). This vessel looped laterally in the right lateral liver lobe, before connecting to the right ventral aspect of the caudal vena cava, with a vascular orifice measuring 5.4 mm (Fig. 1C). While axially rotating the sonographic probe, this opening appeared to extend over approximately 1.5 cm to the From the Department of Clinical Sciences, Faculte´ de Me´decine Ve´te´rinaire, Universite´ de Montre´al, 3200 rue Sicotte, C.P. 5000, Saint-Hyacinthe, QC, Canada J2S 7C6. Address correspondence and reprint requests to Marc-Andre´ d’Anjou, at the above address. E-mail:
[email protected] Received June 14, 2007; accepted for publication July 17, 2007. doi: 10.1111/j.1740-8261.2007.00317.x
Isovuet-300, E.R. Squibb & Sons Company, Princeton, NJ, and Bracco Industria Chimica, Milan, Italy. wHi-Speed ZX/i, General Electric Medical Systems, Mississauga, ON, Canada.
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Fig. 1. Ultrasonographic features of the complex intrahepatic shunt. (A) The portal flow maximal velocity was increased and irregular when measured just caudal to the porta hepatis. The portal vein was normal in size. (B) Sagittal plane of the right caudal portion of the liver. A 1-cm-wide, right-divisional (RD) shunt is looping in the right portion of the liver. The cortex of the right kidney (K) is hyperechoic and a hyperechoic medullary rim sign is identified. (C) Transverse plane, with the marker oriented to the right. The cranial extent of the right-divisional shunt is closely aligned to an aneurysmal-like portion of the portal vein (PV) and enters the caudal vena cava (CVC) through a 5.4 mm orifice (arrow). (D) Transverse oblique plane, with the marker oriented to the right and cranially. A few millimeters more caudally, medially, and ventrally, a second opening () is observed that connects the right-divisional (RD) looping shunt and the main portal vein (PV) segment. On color and spectral Doppler (not shown), the flow appeared bidirectional and turbulent in that opening. Furthermore, the opening between the right-divisional loop and the CVC extends to the dorsal wall of the main portal vein, which is dilated. Arrows show the direction of blood flow into the CVC, through the irregularly shaped foramen.
detailed soft tissue algorithm. Three-dimensional volume rendering was also performed using a diagnostic viewing stationz. On CT-angiographic images, the liver was small and the gallbladder appeared enlarged. The portal vein was larger than the aorta at the level of the porta hepatis, but similar to the caudal vena cava. As seen with ultrasonography, a looping intrahepatic portosystemic shunt was detected in the right lateral liver lobe, reaching up to 1.2 cm in diameter (Figs. 2A and 2B). More cranially and medially, this vessel connected to an aneurysmal-like extension of the portal vein, within the right medial lobe, just ventral to the gallbladder (Figs. 2C and 2D). This lobulated vascular zAW 4.0, General Electric Medical Systems.
pool progressively fused into the adjacent caudal vena cava (Figs. 2D–2F). Contrast enhancement of the shunting loop as well as the aneurysmal portion of the portal vein was less intense than in the adjacent caucal vena cava, which had a clearly demarcated border, up to the level of fusion, more cranially. This finding suggested a membranous separation between the lumen of the closely aligned caudal vena cava and portal vein. However, the size of the orifice between these two structures could not be precisely determined.
Surgical Findings The owners requested euthanasia of the dog, but allowed study of the macroscopic anatomy of the specimen using
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Fig. 2. Contrast-enhanced computed tomographic images of the liver obtained during the portal phase. (A–F) From caudal to cranial. The patient’s right is to the viewer’s left on all images. (A, B) A right-divisional (RD) shunt originates from the right hepatic portal vein (PV) and loops into the right liver. (C) The cranial extent of the right-divisional shunting loop (RD0 ) connects with an abnormal segment of the portal vein, which appears dilated and in close proximity to the caudal vena cava. (D–F) This aneurysmal-like portion of the portal vein gradually blends into the CVC, which becomes enlarged. Ao, aorta; GB, gallbladder.
a described portal venotomy technique.5 After ventral portal venotomy, a first suspicious ostium was found on the right dorsolateral wall of the portal vein, where it normally branches to the right. No other anomalies were visualized through this standard venotomy. A catheter was inserted into the ostium and advanced until it was palpated in the caudal vena cava, confirming the right-divisional shunt. The venotomy was then extended cranially to further expose the anomaly. A second ostium was found cranially, on the ventrolateral aspect of an aneurysmal-like portion of the portal vein. This ampulla progressively fused into the adjacent caudal vena cava through a dorsomedial windowlike opening, exactly as seen in the CT images. Interestingly, the urinary catheter inserted into the looping rightdivisional shunt could be advanced directly into the window-like opening in the caudal vena cava. A small left portal vein branch was located a few millimeters away from the caudal vena cava, opening on the left lateral aspect of the ampulla.
Discussion Intrahepatic portosystemic shunts are classified as left-, central-, or right-divisional, according to the distribution and shape of the shunting vessel.6,7 Central-divisional shunts often have a window-like opening between a dilated portion of the intrahepatic portal vein (right or left branch) and the ipsilateral hepatic vein or caudal vena cava.5,6,8 The adjacent caudal vena cava may also be focally distended. Right- and left-divisional shunts often are curved, tubular to aneurysmal vessels that connect directly to the caudal vena cava or to a hepatic vein. The morphology of an intrahepatic portosystemic shunt must be characterized before surgical or endovascular occlusion as it will influence the feasibility of intervention as well as the technique to be used.9 Congenital intrahepatic and extrahepatic portosystemic shunts are typically single, although multiple congenital shunts have been reported in dogs.10-15 A morphologic
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Fig. 3. Tri-dimensional, volume rendering of the complex portosystemic shunt. Direction of blood flow and shunting orifices are schematized on these ventral (A) and right-lateral (B) views of the vascular anomaly. The peripheral hepatic parenchyma was removed. A right-sided loop originates from the main portal vein (PV) and blends cranially and medially with an aneurysmal portion of the portal vein (arrowheads). This vascular pool progressively blends with the caudal vena cava (CVC) more cranially and dorsally. The shape, size, and location of the foraminal opening (1 and 10 ) between the fused right-divisional loop and aneurysmal portal vein, and the CVC, are shown. A second opening (2 and 20 ) was present between the right-sided loop and the aneurysmal portal vein, through which mild, bidirectional flow was observed with Doppler sonography. Portosystemic shunting was ultimately present only at the larger foraminal opening (1 and 10 ). The location of the left portal vein (LPV), in regard to the foraminal shunt, is also shown.
HUNEAULT
2008
description of multiple intrahepatic portosystemic shunts was provided in only two dogs, in which they appeared as a complex vascular network that involved multiple lobes and that connected to the caudal vena cava.11 In another complex congenital shunt in a dog, an abnormal vessel arising from the left gastric vein was described to join a patent ductus venosus.10 Hepatic arterioportal fistulas may also form a complex pattern of dilated vessels in the liver; however, these can usually be differentiated from venous shunts by the presence of reversed and pulsatile portal flow as well as by the presence of several signs of portal hypertension such as multiple acquired shunts and ascites.13,16,17 To our knowledge, this is the first description of fused right- and central-divisional intrahepatic portosystemic shunts in a dog. Ultrasonographically, the long, right-divisional loop was first identified and appeared classic of this category of intrahepatic portosystemic shunts. A second shunting component, i.e. central divisional, was noticed only after careful inspection of the termination of the first shunt into the caudal vena cava. When compared with CT angiography, the size and location of the orifices, which represent important preinterventional information, were more precisely determined with ultrasonography. Nevertheless, transverse, reformatted, and 3D-rendered CT-angiographic images facilitated the comprehension of shunt morphology and treatment planning (Fig. 3). From a surgical standpoint, only the caudal ostium of the right-divisional loop could be identified after the original portal venotomy. Furthermore, catheterization of this ostium confirmed it as a shunt because the catheter could be felt in the caudal vena cava. Without detailed preoperative imaging, one might have partially or completely occluded this vessel, thinking this would attenuate the portocaval shunt. With the particularities of the intrahepatic shunt described herein, such a treatment would have been incorrect and would result in failure to control the shunt and its clinical effects. In fact, only the cranial window-like opening into the caudal vena cava was hemodynamically significant, i.e. where portosystemic shunting occurred.
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