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Ciência Rural

Print version ISSN 0103-8478On-line version ISSN 1678-4596

Cienc. Rural vol.39 no.5 Santa Maria Aug. 2009  Epub May 01, 2009

https://doi.org/10.1590/S0103-84782009005000084 

ARTIGOS CIENTÍFICOS
CLÍNICA E CIRURGIA

 

Dopplervelocimetric evaluation of portal vein as a diagnostic tool for portosystemic shunt diagnosis in dogs

 

Avaliação dopplervelocimétrica da veia porta como ferramenta diagnóstica de shunt portossistêmico em cães

 

 

Cibele Figueira CarvalhoI, 1; Giovanni Guido CerriII; Maria Cristina ChammasIII

IInstituto de Radiologia (INRAD), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HCFMUSP), 05403-001, São Paulo, SP, Brasil. E-mail: cibelefcarvalho@terra.com.br
IIFaculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brasil
IIIServiço de Ultrassonografia, INRAD, HCFMUSP, São Paulo, SP, Brasil

 

 


ABSTRACT

The objective of this research was to verify if the study of portal hemodynamic parameters through duplex Doppler ultrasonography (DUS) is able to help to detect portosystemic shunt (PSS) and the shunted vessel origin. It was detected PSS in 20 dogs by abdominal DUS and confirmed at surgery or necropsy from March of 2004 until March 2007. Main ultrasonographic findings were: identification of a tortuous vessel shunting portal flow being: portocaval shunt (16/20 or 80%), esplenocaval shunt (2/20 or 10%), gastrocaval shunt (1/20 or 5%), portoazigo shunt (1/20 or 5%); 2) elevated portal flow velocity before shunt (17/20 or 81%), 3) lower portal flow velocity after shunt (17/20 or 81%), 4) turbulence in the caudal vena cava (10/20 or 47,5%) and 5) reduced liver size (15/20 or 71%). The others ultrasonographic findings associated with clinical records were similar to that described in literature. With this work we could conclude that hemodynamic assessment of portal vein with DUS may be a useful tool for PSS diagnosis and to detect the shunted vessel origin.

Key words: ultrasonography, Doppler, portosystemic shunt, dog.


RESUMO

O objetivo desta pesquisa foi verificar se o estudo dos parâmetros hemodinâmicos, por meio da ultrassonografia duplex Doppler (USD), é capaz de auxiliar na detecção do desvio portossistêmico (DPS) e na origem do vaso desviado. Por meio da USD abdominal, foram detectados, no período de março de 2004 a março de 2007, casos de DPS em 20 cães, os quais foram confirmados pela cirurgia ou necropsia. Os principais achados ultrassonográficos foram: 1) identificação de um vaso tortuoso, desviando o fluxo portal, sendo: desvio portocaval (16/20 ou 80%), desvio esplenocaval (2/20 ou 10%), desvio gastrocaval (1/20 ou 5%), desvio portoázigos (1/20 ou 5%); 2) velocidade de fluxo portal elevada antes do desvio (17/20 ou 81%); 3) velocidade de fluxo portal diminuída após o desvio (17/20 ou 81%); 4) fluxo turbulento na veia cava caudal (10/20 ou 47,5%); e 5) fígado de tamanho diminuído (15/20 ou 71%). Os outros achados ultrassonográficos associados com dados clínicos foram semelhantes aos descritos na literatura. Com este trabalho, pode-se concluir que a avaliação hemodinâmica da veia portal com USD pode ser uma ferramenta diagnóstica útil na detecção do DPS e na origem do vaso desviado.

Palavras-chave: ultrassonografia, Doppler, desvio portossistêmico, cão.


 

 

INTRODUCTION

Portosystemic shunts (PSS) are single or multiple abnormal vascular communications that connect blood from stomach, pancreas, spleen and intestines to systemic circulation without passing through the liver. It can be found in all mammals but affects more frequently dogs (D'ANJOU et al., 2004).

PSS in dogs can be either congenital or acquired. Acquired PSSs develop secondary to portal hypertension and are associated with diseases as cirrhosis, chronic cholangiohepatitis, hepatic neoplasia and arteriovenous fistulas. Portal hypertension may result in the formation of multiple extrahepatic shunts, with were previously nonfunctional remnant vessels of the portal system (FERREL et al., 2003). Congenital form is more commonly recognized (LAMB, 1998). Congenital PSSs are anomalous embryonal vessels that usually occur as single shunts (either intra or extra hepatic). The genetic basis for PSSs is unknown, although affected lines have been recognized in miniature Schnauzers, Irish Wolfhound, Old English Sheepdog and Cairn Terriers (FAVERZANI et al., 2003). An autossomal polygenic mechanism is suspected in Irish Wolfhounds (HERDEN et al., 2003). Acquired PSSs, with form is related with portal hypertension symptoms, are multiple extra hepatic shunts that connect the portal system and the caudal vena cava (FERREL et al., 2003). Single intrahepatic PSS provide a communication between portal vein and caudal vena cava (LAMB & WHITE, 1998). They can be classified as left, central and right divisional. The morphology of the left divisional shunt is consistent with failure to close of the fetal ductus venous. The mechanisms associated to this failure are unknown. The pathogenesis of intrahepatic PSSs that occur in the right medial or lateral liver lobes is also unknown. Single intrahepatic PSSs are most common in large breed dogs (HUNT et al., 2000).

Extrahepatic PSSs usually connect the portal vein or one of this tributaries (left gastric or splenic vein) with the caudal vena cava cranial to the phrenicoabdominal veins. The anomalous vessel can eventually enter the azigos vein or other systemic vessel. Single extrahepatic PSSs are most common in cats and small breed dogs (HUNT et al., 2000).

Congenital PSS occur more frequently in purebred dogs. Breeds at increased risk are miniature Schnauzer, Yorkshire terrier, Irish wolfhound, Cairn terrier, Maltese, Golden Retriever, Old English Sheepdog and Labrador (BREZNOCK & WHITING, 1995). It can be found either in Shih Tzu and Poodle (HUNT et al., 2000). Literature still suggests that there is a slight sexual predilection for female dogs (HOLT et al., 1995). Age is a important diagnostic clue because most animals develop signs by six months of age (FERREL et al., 2003; TISDALL et al., 2000).

Clinical signs of congenital PSS can indicate that central nervous system, gastrointestinal system or urinary tract involved (SCHERMERHORN et al., 1996. This disease leads to hepatic atrophy and clinical signs related to the bypass of toxins such as ammonia, resulting in hepatic encephalopathy signs and nephropathy sometimes (FAVERZANI et al., 2003). It must be considered as differential diagnosis microvascular hepatic dysplasia (SCAVELLI et al., 1986); infectious diseases (WRIGLEY et al., 1987); hydrocephaly, idiopathic epilepsy and metabolic diseases as hypoglycemia and thiamine default (D'ANJOU et al., 2004). In dogs and cats with congenital PSS, the liver is usually small. Biopsy findings are indistinguishable from those in hepatic microvascular dysplasia (SCAVELLI et al., 1986).

Color Doppler ultrasound is a useful noninvasive diagnostic tool for evaluate animal with suspicious congenital PSS. Intrahepatic PSS are easier to detect than extrahepatic (LAMB & WHITE, 1998). Liver usually appears small (microhepatica) at the B mode ultrasonography; there is a consistent decrease in number and size of intrahepatic veins (LAMB & WHITE, 1998). Color Doppler mapping can help to identify the presence of an anomalous and tortuous vessel, usually near left kidney or spleen following to caudal vena cava. At the site of communication often it could be seen a turbulence flow (SZATMÁRI et al., 2004). The shunting vessel usually is origin at main portal vein, splenic or gastric vein (BREZNOCK & WHITING, 1995). Pulsed Doppler can revel increased hepatic vascular impedance with increased velocity of blood flow at portal vein in 70% of affected dogs (LAMB,1996).

Normal mean portal blood flow velocity was determined as 18.1±7.6cm s-1 in the literature (KANTROWITZ et al., 1989; NYLAND & FISHER, 1990). Hemodynamic evaluation of portal vein at the sites before and after shunting vessel has not been previously reported in veterinary literature. The mean of this research was evaluating hemodynamic behavior of portal vein in dogs with PSS and verify the utility of duplex Doppler ultrasound to detect the shunting vessel origin at PSS cases.

 

METHODS

Twenty dogs of several breeds have been selected, body weight and ages, whose PSS diagnosis were detected by DUS and confirmed at surgery or necropsy from March 2004 to March 2007. Owner consent was obtained before all procedures. A pulsed duplex Doppler ultrasound was used (GE®, Logiq 3 model) with convex multi frequencials scanners, 3,0 to 5,0MHz, and 4,0 to 6,0MHz and still a linear scanner with 7 to 10MHz.

Dogs were fasted for 6 hours before exam. All dogs had their abdominal area clipped, including right lateral side since 10th intercostal space, and acoustic gel was applied to the skin. Dogs were positioned in dorsal recumbency and ultrasound was performed at this sequence: B-mode, color and pulsed Doppler.

All abdominal organs were scanned by longitudinal, transverse and coronal sonographic planes. Epigastric area was scanned by color mapping to evaluate vascular architecture. It was observed aorta, cranial mesenteric, celiac, gastric and splenic arteries; caudal vena cava, main portal and hepatic veins were also examined. Hepatic artery was observed when possible. It was performed a detailed research to find an anomalous tortuous vessel shunting portal blood circulation intra and/or extra hepatic. After color mapping, the cursor of pulsed Doppler was positioned at the center of vessel lumen to be analyzed, with special attention to the angle of insonation. This angle was maintained at 60° or less during the study of each vessel, and as parallel as possible to blood flow to measure velocities. It was gotten spectral Doppler of cranial mesenteric and aorta arteries, one hepatic vein and main portal vein at two distinct sites (before and after shunt), caudal vena cava and hepatic artery when was possible. Maximal systolic and final diastolic velocities of each mentioned artery were measured. Maximal systolic velocity were measured of each vein. The data were recorded, and calculated means and percentages. Velocities results were submitted to paired t test with confidence interval of 95% or statistical significance defined as P<0.05.

 

RESULTS AND DISCUSSION

All data was presented in table 1. From the twenty dogs examinated with PSS, the following breed distribution were obtained: Yorkshire (5/20 or 25%), Shih Tzu (4/20 or 20%), Lhasa Apso (2/20 or 10%), mixed breed (2/20 or 10%), and Maltese, Spitz, Poodle, Border collie, Miniature Schnauzer, Cairn terrier, Rottweiler (1/20 or 5% each one). These distribution seems similar that described in the literature (FAVERZANI et al., 2003; HUNT et al., 2000; BREZNOCK & WHITING, 1995). The mean age was 17 months indicate that this disease often appears in young dogs as cited elsewhere (FERREL et al., 2003; TISDALL et al., 2000). It has not observed sexual predilection.

According data recorded (Table 1) it was observed that 80% of the selected dogs with PSS presented portocaval shunt (Figure 1). Splenocaval shunt (Figure 2) was the second more common accounting 10%, while gastrocaval and portoazigos shunts were found in 5% each. These data confirm the findings related at veterinary literature that shows portocaval as the most frequent PSS in dogs (D'ANJOU et al., 2004; LAMB & WHITE, 1998; HUNT et al., 2000).

In 15% (3/20) of dogs was not possible to obtain two different measures at two sites of main portal vein. And one of them has elevated blood flow velocity at main portal vein. The others dogs (17/20) or 85% presented elevated blood flow velocity at main portal vein before the shunting vessel origin when comparing at the site after the shunting vessel origin (Figure 2). It was found a statistical difference (P > 0.05) between these velocities before and after shunt.

It was found in 60% (12/20) of dogs an elevated main portal vein velocity with maximal systolic velocity upper normal limits established in literature (KANTROWITZ et al., 1989; NYLAND & FISHER, 1990). Another research done before (LAMB, C.R.,1996) have found that 70% of affected dogs presented elevated portal vein velocity. These increased velocities are results of the associated hemodynamic disturbances depending on the location of the shunt as reported in the literature (SZATMÁRI et al., 2004).

Those dogs with normal values of blood flow velocity at main portal vein before shunt presented lower values at the site after shunt. This lower flow was the result of the blood dividing, with some blood flowed via the shunt toward systemic circulation and some to the portal vein. Because the dual hepatic blood supply, where in approximately 75% of hepatic flow arrives via the portal vein, deviation of flow determines disturbances in hemodynamic equilibrium. Duplex Doppler ultrasonography can detect pathological blood flow. The hemodynamic behavior of portal vein in dogs with PSS demonstrates differences between velocities obtained before and after the site at shunting vessel origin. And the difference between these velocities also were statistical significant. These data suggests that this difference between velocities could help to identify the PSS and to find the anomalous vessel shunting origin.

 

CONCLUSIONS

The hemodynamic study of portal vein using duplex Doppler ultrasound can be a useful tool to the PSS diagnosis. Differences between velocities in portal vein could help to identify the PSS and to find the anomalous vessel shunting origin. The results of this work show a national statistical data. That could help clinicians to think about that PSS diagnosis could be made using the tools that we have.

 

REFERENCES

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Received 08.19.08
Approved 02.13.09

 

 

1 Autor para correspodêcia.

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