Morphological and hemodynamic changes in the portal venous system after distal splenorenal shunt: an ultrasound and pulsed Doppler study

Visualization of two-dimensional transverse blood flow direction using optical coherence tomography angiography

SIGNIFICANCE

Evaluation of vessel patency and blood flow direction is important in various medical situations, including diagnosis and monitoring of ischemic diseases, and image-guided vascular surgeries. While optical coherence tomography angiography (OCTA) is the most widely used functional extension of optical coherence tomography that visualizes three-dimensional vasculature, inability to provide information of blood flow direction is one of its limitations.

AIM

We demonstrate two-dimensional (2D) transverse blood flow direction imaging in en face OCTA.

APPROACH

A series of triangular beam scans for the fast axis was implemented in the horizontal direction for the first volume scan and in the vertical direction for the following volume scan, and the inter A-line OCTA was performed for the blood flow direction imaging while the stepwise pattern was used for each slow axis scan. The decorrelation differences between the forward and the backward inter A-line OCTA were calculated for the horizontal and the vertical fast axis scans, and the ratio of the horizontal and the vertical decorrelation differences was utilized to show the 2D transverse flow direction information.

RESULTS

OCTA flow direction imaging was verified using flow phantoms with various flow orientations and speeds, and we identified the flow speed range relative to the scan speed for reliable flow direction measurement. We demonstrated the visualization of 2D transverse blood flow orientations in mouse brain vascular networks in vivo.

CONCLUSIONS

The proposed OCTA imaging technique that provides information of 2D transverse flow direction can be utilized in various clinical applications and preclinical studies.

Doppler sonography of the native liver

Doppler sonography is being used routinely in evaluating the vascular structures of the native liver because of its ease of use, lower cost, easier availability, lack of need for X-ray and accuracy. Doppler sonography can well demonstrate the vascularization of liver tumors, portal vein thrombosis, portal vein abnormalities in patients with portal hypertension and hepatic venous findings in patients with Budd Chiari syndrome. The purpose of this article is to present information about Doppler sonography of the native liver and to show its usefulness in the evaluation of hepatic vascular diseases.

[Duplex ultrasound of the liver and portal vein system]

Duplex ultrasound allows direct access to portal venous and hepatic vein hemodynamics. This method has been accepted as a reliable procedure to detect portal and splenic venous thrombosis, Budd-Chiari's syndrome, portosystemic collateralisation and changes in the portal venous blood flow direction with a high rate of sensitivity. Besides these qualitative findings Doppler flowmetry allows quantitative measurement of portal venous blood flow velocities. The estimation of portal hypertension and the prediction of the risk of variceal bleeding by quantitative Doppler flowmetry is of increasing clinical importance. In monitoring the efficiency of medicational prophylaxis against gastrointestinal bleeding is also helpful. Duplex ultrasound can be used to evaluate the function of portocaval shunts including the intrahepatic stent shunt as well as to detect vascular complications after liver transplantation. Furthermore the method is gaining importance in the diagnosis and monitoring of therapy of acute liver transplant rejection. In case of liver tumors duplex ultrasound is of value for tumor staging and provides information about the dignity on the basis of perfusion patterns.

Sonographic diagnosis of hepatic vascular disorders

Perhaps the most valuable application of duplex sonography in the abdomen is in the diagnosis of vascular disorders of the liver. Duplex sonography provides an accurate assessment of the portal and hepatic venous systems that is both noninvasive and convenient, because the examination can be conducted at the bedside. In this article, the normal features of portal and hepatic venous flow are considered as well as the sonographic manifestations of pathological conditions, including: (1) portal hypertension; (2) portosystemic collaterals; (3) portal vein thrombosis; and (4) hepatic vein thrombosis (Budd-Chiari syndrome).

Portal vein thrombosis associated with rectal bleeding: non-invasive diagnosis and follow up by ultrasound

A 65 year old woman presented with a sudden onset of abdominal pain and bright rectal bleeding. Shortly after admission a diagnosis of partial portal vein thrombosis was made by ultrasonography. This thrombosis appeared to be the first sign of a previously unsuspected hypercoagulable state due to polycythaemia rubra vera. Ultrasound proved useful in confirming complete resolution of the portal system thrombosis in response to conservative therapy.

The effect of splenomegaly on splanchnic hemodynamics in nonalcoholic cirrhosis after distal splenorenal shunt and splenopancreatic disconnection

We investigated the effect of splenomegaly on portal hemodynamics during and after distal splenorenal shunt with splenopancreatic disconnection in 27 patients with nonalcoholic cirrhosis (13 with and 14 without splenic enlargement). Data were obtained by Doppler flowmetry, electromagnetic flowmetry and computed tomographical scanning. The splenomegaly group had a significantly higher preoperative splenic and portal blood flow than the nonsplenomegaly group. In both groups, postoperative portal venous pressure did not fall; portal blood flow significantly decreased while splenic volume was reduced, despite the lack of significant changes in splenic venous blood flow. There was a greater reduction of portal blood flow with previous splenomegaly than with normal-sized spleens, and this was not related to the degree of reduction in liver volume. In the splenomegaly group, the increase of splenic blood flow was only present during the early postoperative period. In conclusion, distal splenorenal shunt with splenopancreatic disconnection influenced portal hemodynamics differently in nonalcoholic cirrhotic patients with and without splenomegaly.

Long-term effects of distal splenorenal shunt on hepatic hemodynamics and liver function in patients with cirrhosis: importance of reversal of portal blood flow

We studied 23 patients with cirrhosis who had undergone retroperitoneal distal splenorenal shunt without portal-azygos disconnection more than 2 yr earlier. We investigated the suitability of the Doppler technique (ultrasound + Doppler) to assess the patency and blood flow direction through the portal vein and the distal splenorenal shunt and its correlation with the continuous thermal dilution technique. The study also assessed the influence of the distal splenorenal shunt and time after surgery on portal perfusion and liver function. Ultrasound + Doppler distal splenorenal shunt thrombosis in two patients; however, none was confirmed by continuous thermal dilution. Ultrasound + Doppler flowmetry was possible in 19 patients (83%) (mean, 1.58 +/- 0.53 L/min). Distal splenorenal shunt continuous thermal dilution measurements were performed in all patients (100%), (mean, 1.65 +/- 0.5 L/min). Good correlation was seen between them (r = 0.66). Ultrasound + Doppler of the portal vein showed a hepatopetal flow in 16 patients (69.9%). Hepatic blood flow was significantly higher in patients with hepatopetal flow (p = 0.003). Hepatic clearance and intrinsic hepatic clearance of indocyanine green were significantly lower in patients with hepatofugal flow. Patients with hepatofugal flow had a higher incidence of chronic encephalopathy. None of the patients with a follow-up of less than 4 yr exhibited hepatofugal flow, whereas 7 of the 16 patients with a longer follow-up had hepatofugal flow (43.7%). The difference was statistically significant (p = 0.04). This study suggests that ultrasound + Doppler sonography may provide useful data in the evaluation of the patency and blood flow direction through the portal vein and the distal splenorenal shunt.(ABSTRACT TRUNCATED AT 250 WORDS)

The distal splenorenal shunt

Distal splenorenal shunt (DSRS) provides selective decompression of gastroesophageal varices, with maintenance of portal hypertension and prograde portal flow to the cirrhotic liver. Accurate patient evaluation is essential to select appropriate patients for DSRS. Variceal bleeding control is greater than 85% and is as effective as total portosystemic shunts. Maintenance of prograde portal flow is greater than 90% in nonalcoholic disease, but only 50% in alcoholic cirrhosis; the latter is improved by total splenopancreatic disconnection. Hepatic function is better maintained when portal flow is maintained. Encephalopathy is lower after DSRS than after total shunts. Survival is not significantly improved after DSRS in patients with alcoholic cirrhosis compared to outcome after total shunts. The survival in patients with nonalcoholic disease is significantly improved over that of alcoholics.