Vascular Plug-Assisted Retrograde Transvenous Obliteration for the Treatment of Gastric Varices and Hepatic Encephalopathy: A Prospective Multicenter Study

Interventional Radiology Management of Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a clinically severe and devastating complication of decompensated liver disease affecting mortality, quality of life for patients and families, hospital admission rates, and overall health-care costs globally. Depending on the cause of HE, several medical treatment options have been developed and become available. In some refractory HE, such as spontaneous portosystemic shunt-related HE (SPSS-HE) or posttransjugular intrahepatic portosystemic shunt HE (post-TIPS HE), advanced interventional radiology (IR) procedures have been used, and shown to be effective in these conditions. This review presents 2 effective IR procedures for managing SPSS-HE and post-TIPS HE.

The Management of Hepatic Encephalopathy from Ward to Domiciliary Care: Current Evidence and Gray Areas

Hepatic encephalopathy (HE) is a common complication of advanced liver disease and acute liver failure. It is a condition that features several neuropsychiatric symptoms that affect mortality, morbidity and the quality of patients' and caregivers' lives. An HE diagnosis is generally an exclusion diagnosis. Once the patient is admitted to the hospital, clinical examination, blood tests and eventually neuroimaging should be performed with the aim of ruling out other causes of acute brain dysfunction. Moreover, HE is recognized using various precipitants that can potentially promote its onset, alone or in combination, and must be identified. Once the diagnostic process is complete, a correct treatment should be started. The anti-HE treatment is based on a combination of the correction of precipitants; non-absorbable antibiotics, such as rifaximin; and non-absorbable disaccharides. Once the patient is discharged from the hospital, specific anti-HE therapy should be maintained in order to prevent other HE episodes.

Plug-assisted Retrograde Transvenous Obliteration-II for Gastric Varices: A Case Report

We present a case of gastric varices successfully treated with modified plug-assisted retrograde transvenous obliteration. A 45-year-old male patient had isolated fundal gastric varices caused by alcoholic cirrhosis. Contrast-enhanced computed tomography showed that the gastric varices were drained mainly via the gastro-renal shunt. The gastric varices were treated via plug-assisted retrograde transvenous obliteration using an IMPEDE vascular plug with a modified coil-assisted retrograde transvenous obliteration-II procedure. There were no complications during the procedure, and an endoscopic examination 3 months after the procedure revealed that the gastric varices had disappeared. To our knowledge, this is the first report on the application of plug-assisted retrograde transvenous obliteration-II using a newly designed IMPEDE vascular plug to avoid migration of the sclerosant.

Efficacy and Technical Feasibility of Plug-Assisted Retrograde Transvenous Obliteration of Gastric Varices via Pathways Other than the Gastrorenal Shunt

PURPOSE

To evaluate the efficacy and technical feasibility of plug-assisted retrograde transvenous obliteration of gastric varices via pathways different from the typical gastrorenal shunt.

MATERIALS AND METHODS

We retrospectively reviewed the medical records of 130 patients who underwent plug-assisted retrograde transvenous obliteration for gastric varices between 2013 and 2022. Eight patients underwent plug-assisted retrograde transvenous obliteration via different pathways. We evaluated the types of portosystemic shunts in these patients, the procedure technical and clinical success rates, and clinical outcomes.

RESULTS

In these eight patients (6 males, 2 females; mean age = 60 ± 6 years), the most common type of portosystemic shunt was a gastrocaval shunt (n = 7). Five patients had a gastrocaval shunt only; two had coexisting gastrocaval and gastrorenal shunts. One patient had a pericardiacophrenic shunt without a gastrorenal or gastrocaval shunt. The mean procedure time was 55 min. For patients with a gastrocaval shunt alone (n = 5), the mean procedure time was 40.8 min. The technical and clinical success rates were 100%. No major complication related to the procedure occurred. An initial follow-up computed tomography was performed within 2-3 weeks in all patients and revealed complete thrombosis of the gastric varices. Subsequent follow-up computed tomography (interval: 2-6 months) was performed in seven patients and showed complete disappearance of the gastric varices in all patients. During the follow-up period (range: 42 days-6.25 years), no patients experienced rebleeding or recurrence of gastric varices.

CONCLUSION

Plug-assisted retrograde transvenous obliteration via alternative portosystemic shunts is effective and technically feasible in the treatment of gastric varices.

Old and New Precipitants in Hepatic Encephalopathy: A New Look at a Field in Continuous Evolution

Hepatic encephalopathy (HE) is a common complication in patients with advanced liver disease. It is a brain dysfunction characterized by neurological and psychiatric symptoms that significantly affects quality of life, morbidity and mortality of patients. HE has various precipitants that can potentially promote its onset, alone or in combination. Among the historically well-known precipitants, such as infections, gastrointestinal bleeding, dehydration, electrolyte disorders and constipation, recent studies have highlighted the role of malnutrition and portosystemic shunts as new precipitating factors of HE. The identification, management and correction of these factors are fundamental for effective HE treatment, in addition to pharmacological therapy with non-absorbable disaccharides and/or antibiotics.

Short-Term Results of Plug-Assisted Retrograde Transvenous Obliteration for Portal Steal from Complicated Portosystemic Shunts in Living-Donor Liver Transplantation

PURPOSE

To investigate the effectiveness of plug-assisted retrograde transvenous obliteration (PARTO) for portal steal from complicated portosystemic shunts (PSSs) in living-donor liver transplantation (LDLT).

MATERIALS AND METHODS

This retrospective study included consecutive patients who underwent LDLT and intraoperative or postoperative PARTO for complicated PSS between January 2020 and December 2021. PARTO was performed when hepatofugal portal flow steal was identified during intraoperative cineportography, and afferent vein embolization was difficult because of multiple afferent veins or incomplete afferent vein embolization. Liver volume, complete obliteration of PSS, technical success, adverse events, and follow-up clinical and laboratory data were evaluated.

RESULTS

Thirty-seven patients were included, and the technical success rate was 100% with no major adverse events. During the median follow-up of 20.0 months, all patients recovered well with suitable regeneration of the liver without graft dysfunction related to a portal steal. The liver volume significantly increased within 1 month (median, 956 vs 1,198 mL; P < .001). Complete obliteration of a PSS occurred in 36 of 37 (97.3%) patients, and there was no recurrence during follow-up. The Child-Pugh score, serum albumin and total bilirubin levels, and prothrombin time showed significant improvement over serial follow-up. Compared with preprocedural values (14.9 cm/s), follow-up portal flow (median) peaked on the first day (71.2 cm/s, P < .001) and then remained significantly high at 1 week (60.3 cm/s, P < .001) and 1 month (53.1 cm/s, P < .001), in accordance with the graft regeneration.

CONCLUSIONS

PARTO is an effective procedure for the treatment of complicated PSS in LDLT.

Management of Refractory Variceal Bleed in Cirrhosis

Acute variceal bleeding is the major cause of mortality in patients with cirrhosis. The standard medical and endoscopic treatment has reduced the mortality of variceal bleeding from 50% to 10-20%. The refractory variceal bleed is either because of failure to control the bleed or failure of secondary prophylaxis. The patients refractory to standard medical therapy need further interventions. The rescue therapies include balloon tamponade, self-expanding metal stents (SEMS) placement, shunt procedures, including transjugular intrahepatic portosystemic shunt (TIPS), balloon-occluded retrograde transvenous obliteration (BRTO), and endoscopic ultrasound (EUS) guided coiling. In cases where endoscopic variceal ligation (EVL) has failed and the variceal bleeding continues, temporary measures like balloon tamponade can be used to achieve hemostasis and as a bridge to definitive measures. SEMS being in use for refractory bleed is preferred over balloon tamponade due to the reduced complication rate. The shunting procedures are highly effective in reducing portal pressure and represent the gold standard for uncontrolled variceal bleeding. The surgical shunts, as well as nonshunt surgeries such as devascularization have become less popular with the increasing use of minimally invasive techniques like TIPS. TIPS have high success rates in controlling refractory variceal bleeding. The mortality rate is greater in high-risk patients undergoing salvage TIPS, and hence, pre-emptive TIPS should be considered in these patients. BRTO is an interventional radiologic procedure used in the management of bleeding gastric and ectopic varices. The availability of gastrorenal or splenorenal shunts is required for the BRTO procedure, which helps to reach and obliterate the cardiofundal varices through the femoral or jugular vein approach. The EUS guided coiling and glue injection have shown promising results, and further randomized controlled trials are required to establish their efficacy for refractory variceal bleeding.

Balloon-occluded retrograde transvenous obliteration for treatment of gastric varices

Rupture of gastric varices (GVs) can be fatal. Balloon-occluded retrograde transvenous obliteration (BRTO), as known as retrograde sclerotherapy, has been widely adopted for treatment of GVs because of its effectiveness, ability to cure, and utility in emergency and prophylactic treatment. Simplifying the route of blood flow from GVs to the gastrorenal shunt is important for the successful BRTO. This review outlines BRTO indications and contraindications, describes basic BRTO procedures and modifications, compares BRTO with other GVs treatments, and discusses various combination therapies. Combined BRTO and partial splenic embolization may prevent exacerbation of esophageal varices and shows promise as a treatment option.

Retrograde transvenous obliteration for the prevention of variceal rebleeding in patients with hepatocellular carcinoma: a multicentre retrospective study

AIM

To evaluate the effectiveness and safety of retrograde transvenous obliteration (RTO) for the prevention of variceal rebleeding variceal rebleeding in patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

This multicentre retrospective study enrolled 79 patients with HCC who underwent RTO for the prevention of variceal rebleeding. Successful occlusion of the gastrorenal shunt and obliteration of the gastric varices were achieved in 74 patients, with a technical success rate of 93.7%. Of the remaining 74 patients (mean age, 64.9±10.3 years; 56 men), 66 (90.4%) had gastroesophageal varices and seven (9.6%) had isolated gastric varices. Thirty-two patients (43.8%) underwent balloon-occluded RTO, 40 patients (54.8%) underwent plug-assisted RTO, and one patient (1.4%) underwent coil-assisted RTO. No patients had major procedural complications.

RESULTS

Rebleeding occurred in seven patients (9.6%) during the follow-up period. The 6-week and 1-year actuarial probabilities of patients remaining free of rebleeding were 90.8±3.6% and 88.6±4.1%, respectively. The median survival was 12.6 (95% confidence interval [CI] 8-17.3) months. The 6-week, 1-year, and 3-year actuarial probabilities of survival were 83.2±4.4%, 51.1±6.6%, and 32.7±7%, respectively. New or worsening ascites and oesophageal varices occurred in 12 (16.4%) and 13 patients (17.8%), respectively, during the follow-up period. Overt hepatic encephalopathy occurred in one patient (1.4%) during the follow-up period. The Child-Pugh score remained comparable to that at baseline at 1 and 3 months.

CONCLUSION

RTO was effective and safe in preventing variceal rebleeding in patients with HCC.

The Application of Interventional Radiology in Living-Donor Liver Transplantation

Owing to improvements in surgical techniques and medical care, living-donor liver transplantation has become an established treatment modality in patients with end-stage liver disease. However, various vascular or non-vascular complications may occur during or after transplantation. Herein, we review how interventional radiologic techniques can be used to treat these complications.

Successful retrograde transvenous obliteration for splenorenal shunts after liver ransplantation: Midterm results

BACKGROUND/AIMS

The objective of this study was to evaluate the use of Amplatzer-assisted retrograde transvenous obliteration (RTO) in patients with splenorenal shunts (SRSs) after orthotopic liver transplantation (OLT).

MATERIALS AND METHODS

From August 2015 to March 2017, 5 patients received RTO at our center because of SRSs after OLT. The clinical features of the patients with SRSs included demographics, donor type, new-onset symptoms, liver function tests, imaging examinations, interventional examinations and treatments, and outcomes. The patients who received RTO were regularly monitored, and data were gathered before and after the procedures and compared using the paired-sample t test.

RESULTS

Percutaneous interventional management was successfully undertaken in all patients, and 5 Amplatzers and 2 stents were also implanted successfully in patients owing to portal vein (PV) stenosis. There were no procedure-related complications in these patients. In all 5 patients with SRSs, 2 weeks after the interventional therapy, the computed tomography findings showed that the splenic renal shunt vein was completely blocked. The mean blood pressure in the donor lateral PV and the mean blood flow velocity of the donor lateral PV after RTO were all improved significantly (p<0.05). It also suggested that all 5 patients with SRSs survived, with the primary graft functioning normally at the final follow-up.

CONCLUSION

Amplatzer-assisted RTO is a safe and effective treatment for SRSs after OLT. Considering the complexity of the diagnosis and treatment of SRSs in liver transplantation, this complication should be taken seriously.

Combined Transjugular Intrahepatic Portosystemic Shunt Plus Variceal Obliteration versus Transjugular Intrahepatic Portosystemic Shunt Alone for the Management of Gastric Varices: Comparative Single-Center Clinical Outcomes

PURPOSE

To compare the safety and clinical outcomes of combined transjugular intrahepatic portosystemic shunt (TIPS) plus variceal obliteration to those of TIPS alone for the treatment of gastric varices (GVs).

MATERIALS AND METHODS

A single-center, retrospective study of 40 patients with bleeding or high-risk GVs between 2008 and 2019 was performed. The patients were treated with combined therapy (n = 18) or TIPS alone (n = 22). There were no significant differences in age, sex, model for end-stage liver disease score, or GV type between the groups. The primary outcomes were the rates of GV eradication and rebleeding. The secondary outcomes included portal hypertensive complications and hepatic encephalopathy.

RESULTS

The mean follow-up period was 15.4 months for the combined therapy group and 22.9 months for the TIPS group (P = .32). After combined therapy, there was a higher rate of GV eradication (92% vs 47%, P = .01) and a trend toward a lower rate of GV rebleeding (0% vs 23%, P = .056). The estimated rebleeding rates were 0% versus 5% at 3 months, 0% versus 11% at 6 months, 0% versus 18% at 1 year, and 0% versus 38% at 2 years after combined therapy and TIPS, respectively (P = .077). There was no difference in ascites (13% vs 11%, P = .63), hepatic encephalopathy (47% vs 55%, P = .44), or esophageal variceal bleeding (0% vs 0%, P > .999) after the procedure between the groups.

CONCLUSIONS

The GV eradication rate is significantly higher after combined therapy, with no associated increase in portal hypertensive complications. This translates to a clinically meaningful trend toward a reduction in GV rebleeding. The value of a combined treatment strategy should be prospectively studied in a larger cohort to determine the optimal management of GVs.

Relevance of Spontaneous Portosystemic Shunts Detected with CT in Patients with Cirrhosis

Background Cirrhosis leads to portal hypertension and to the consequent formation of spontaneous portosystemic shunts (SPSSs), leading to complications related to the diversion of portal blood into the systemic circulation, which is called portosystemic shunt syndrome. Purpose To investigate the characteristics of patients with cirrhosis and an SPSS and secondarily to assess the prognostic impact of SPSSs on portal hypertension-related complications and transplant-free survival. Materials and Methods A retrospective database review of patients with cirrhosis (observed from March 2015 to July 2019) was performed to identify patients with CT imaging and outcomes data. For each patient, clinical and biochemical data were collected, and the presence, types, and sizes of SPSSs were investigated with CT. Patients were followed for a mean of 27.5 months ± 22.8. Multivariable logistic analysis was used to identify the clinical characteristics associated with the presence of SPSSs (any size) and presence of SPSSs 1 cm or larger. Competitive risk analysis (Fine and Gray model) was used to identify the association between SPSSs and complications and mortality. Results Two hundred twenty-two patients with cirrhosis (157 male, 65 female; mean age, 62 years ± 12 [standard deviation]) were evaluated. An SPSS was found in 141 of 222 patients (63.5%), and 40 of 222 (18%) had a shunt diameter of at least 1 cm. At presentation, variables independently associated with the presence of SPSSs (any size) were portal vein thrombosis (odds ratio, 5.5; P = .008) and Child-Pugh class C (odds ratio, 3.0; P = .03). Previous hepatic encephalopathy (odds ratio, 4.4; P = .001) and portal vein thrombosis (odds ratio, 5.3; P = .001) were the only variables associated with SPSSs larger than 1 cm. Patients with SPSSs of any size had higher mortality (subdistribution hazard ratio, 1.9; P < .001) and higher frequency of hepatic encephalopathy (subdistribution hazard ratio, 2.3; P = .023), gastrointestinal bleeding (subdistribution hazard ratio, 2.9; P = .039), and portal vein thrombosis (subdistribution hazard ratio, 7.6; P = .005). Conclusion The presence of spontaneous portosystemic shunts on CT images in patients with cirrhosis was associated with higher mortality and complications, including portal vein thrombosis, hepatic encephalopathy, and gastrointestinal bleeding. © RSNA, 2021 See also the editorial by Reeder in this issue.

The Promise of Percutaneous Transhepatic Variceal Embolization for Both Gastroesophageal and Ectopic Varices—An Australian Case Series

Purpose This article aims to report Australian experience of percutaneous transhepatic embolization of gastroesophageal and ectopic varices.

Method Eight consecutive patients (mean age 61.8 years, 7 men) who had undergone percutaneous transhepatic variceal embolization (PTVE) for variceal bleeding between October 2013 and February 2020 were analyzed. All patients were admitted from the emergency department. The following embolic materials were used—coils, Onyx 18 (Medtronic), and n-butyl cyanoacrylate plus lipiodol.

Results Post-PTVE, all eight patients demonstrated clinical and radiological improvement in the immediate postprocedure period (< 24 hours). Patients were followed for a mean of 44 ± 24 days postprocedure. Two patients were lost to follow-up. The postprocedure complications included rebleeding (n = 1), hepatic encephalopathy (n = 1), hemoperitoneum (n = 1), ileus (n = 1), and abdominal pain (n = 3).

Conclusion PTVE is an effective treatment option for patients with uncontrolled variceal bleeding (ectopic as well as gastroesophageal) especially when the traditional therapies such as transjugular intrahepatic portosystemic shunts, endoscopic variceal ligation, and balloon-occluded retrograde transvenous obliteration are contraindicated or ineffective.

Change in Portal Pressure and Clinical Outcome in Cirrhotic Patients with Gastric Varices after Plug-Assisted Retrograde Transvenous Obliteration

Background/Aims

Plug-assisted retrograde transvenous obliteration (PARTO) is widely used to manage gastric varices with a portosystemic shunt. It is not clear whether portal pressure and the incidence of complications increase after PARTO. The aim of this study was to determine the changes in portal pressure and the associated changes in liver function, ascites, hepatic encephalopathy, and especially esophageal varix (EV) after PARTO.

Methods

From March 2012 to February 2018, 54 patients who underwent PARTO were analyzed retrospectively. The parameters collected included liver function and episodes of cirrhotic complications before and at 1 and 6 months after PARTO.

Results

The analysis of 54 patients showed improvement in liver function during the 6-month follow-up period (Model for End-Stage Liver Disease score: change from 11.46±4.35 to 10.33±2.96, p=0.021). Among these 54 patients, 25 patients were evaluated for their hepatic venous pressure gradient (HVPG) before and after PARTO (change from 12.52±3.83 to 14.68±5.03 mm Hg; p<0.001). Twenty-five patients with portal pressure measured before and after PARTO were evaluated for risk factors affecting liver function improvement and EV deterioration. No factor associated with portal pressure was affected by liver function improvement. Post-PARTO portal pressure was a risk factor affecting EV deterioration (HVPG-post: odds ratio, 1.341; 95% confidence interval, 1.017 to 1.767; p=0.037).

Conclusions

The artificial blockade of the portosystemic shunt evidently leads to an increase in HVPG. Liver function was improved over the 6-month follow-up period. Portal pressure after PARTO was a significant risk factor for EV deterioration. Portal pressure measurement is helpful for predicting the patient's clinical outcome.

Management of portal hypertension severe complications

Portal hypertension is a clinical syndrome characterized by an increase in the portal pressure gradient, defined as the gradient between the portal vein at the site downstream of the site of obstruction and the inferior vena cava. The most frequent cause of portal hypertension is cirrhosis. In patients with cirrhosis, portal hypertension is the main driver of cirrhosis progression and development of hepatic decompensation (ascites, variceal hemorrhage and hepatic encephalopathy), which defines the transition from compensated to decompensated stage. In decompensated patients, treatments aim at lowering the risk of death by preventing further decompensation and/or development of acute-on-chronic liver failure. Decompensated patients often pose a complex challenge which typically requires a multidisciplinary approach. The aims of the present review were to discuss the current knowledge regarding interventional treatments for patients with portal hypertension complications as well as to highlight useful information to aid hepatologists in their clinical practice. Specifically, we discussed the indications and contraindications of transjugular intra-hepatic portosystemic shunt and for the treatment of gastro-esophageal variceal hemorrhage in patients with decompensated cirrhosis (first section); we reviewed the use of interventional treatments in patients with hepatic vein obstruction (Budd-Chiari Syndrome) and in those with portal vein thrombosis (second section); and we briefly comment on the most frequent applications of selective splenic embolization in patients with and without underlying cirrhosis (third section).

Spontaneous portosystemic shunts in liver cirrhosis: new approaches to an old problem

Portal hypertension is the main consequence of liver cirrhosis, leading to severe complications such as variceal hemorrhage, ascites or hepatic encephalopathy. As an attempt to decompress the portal venous system, portal flow is derived into the systemic venous system through spontaneous portosystemic shunts (SPSSs), bypassing the liver. In this review, we aim to provide an overview of the published reports in relation to the prevalence and physiopathology behind the appearance of SPSS in liver cirrhosis, as well as the complications derived from its formation and its management. The role of SPSS embolization is specifically discussed, as SPSSs have been assessed as a therapeutic target, mainly for patients with recurrent/persistent hepatic encephalopathy and preserved liver function. Furthermore, different aspects of the role of SPSS in liver transplantation, as well as in candidates for transjugular intrahepatic portosystemic shunt are reviewed. In these settings, SPSS occlusion has been proposed to minimize possible deleterious effects, but results are so far inconclusive.

Retrograde Transvenous Obliteration (RTO): A New Treatment Option for Hepatic Encephalopathy

Hepatic Encephalopathy (HE) is a complication of liver disease, consisting of brain dysfunction often due to portosystemic shunting of blood flow in the liver. HE can range from minimal HE, presenting with normal neurological function, to overt HE, with neurological and neuropsychiatric abnormalities. Various clinical grading systems are used to differentiate HE to provide the appropriate treatments. Traditional treatment of HE aims to identify and resolve precipitating factors through targeting hyperammonemia and administering antibiotics or probiotics. While retrograde transvenous obliteration (RTO), including balloon-occluded retrograde transvenous obliteration, coil-assisted retrograde transvenous obliteration or plug-assisted retrograde tranvenous obliteration, is an established procedure to manage gastric varices, little is known about its potential to treat HE. RTO is a procedure to occlude a spontaneous portosystemic shunt, minimizing shunting of portal blood to systemic circulation. Though there is not a large study with HE patients who have undergone RTO; the results appear promising in reducing HE. Side effects, however, should be considered in the treatment of HE such as the transient worsening of portal hypertension and the formation of additional shunts. While additional studies are needed to assess the long-term success, RTO appears to be an effective alternative method to alleviate clinical symptoms of HE when pharmacological therapies and other conservative medical managements have failed.

Retrograde transvenous obliteration for the prevention of variceal rebleeding in patients with portal vein thrombosis: a multicenter study

OBJECTIVES

To evaluate the effectiveness of retrograde transvenous obliteration (RTO) for the prevention of variceal rebleeding in cirrhotic patients with portal vein thrombosis (PVT).

METHODS

Consecutive cirrhotic patients with PVT who underwent RTO for the prevention of variceal rebleeding between January 2002 and June 2019 were included in this multicenter retrospective study. The primary outcome measure was rebleeding. The secondary outcome measures were survival, other complications of portal hypertension, liver function, and PVT.

RESULTS

Forty-five patients (mean age, 66.0 ± 10.6 years; mean Model for End-Stage Liver Disease (MELD) score, 13.9 ± 5.5) were included. The 1-year actuarial probability of remaining free of rebleeding was 92.8 ± 4.0%. The 6-week, 1-year, and 3-year actuarial probabilities of survival were 79.8 ± 6.0%, 48.8 ± 7.7%, and 46.1 ± 7.9%, respectively. MELD score (hazard ratio (HR), 1.09 (95% confidence interval (CI), 1.01-1.17); p = .013) and ascites (HR, 2.84 (95% CI, 1.24-6.55); p = .014) were identified as significant predictors of survival. The 1-year actuarial probabilities of remaining free of new or worsening ascites and esophageal varices were 81.2 ± 8.7% and 89.2 ± 6.0%, respectively. No patients had overt hepatic encephalopathy during follow-up. MELD score significantly increased by a mean of 3.8 (95% CI, 1.7-6.0) at 3 months (p = .001). PVT had improved in 32.0%, worsened in 12.0%, and remained unchanged in 56.0% of patients at 3 months.

CONCLUSION

RTO may be effective for the prevention of variceal rebleeding in cirrhotic patients with PVT.

KEY POINTS

• Retrograde transvenous obliteration may prevent variceal rebleeding in cirrhotic patients with portal vein thrombosis. • The risks of other complications of portal hypertension may not be high after retrograde transvenous obliteration in cirrhotic patients with portal vein thrombosis. • Portal vein thrombosis may improve in approximately one-third of cirrhotic patients within 3 months after retrograde transvenous obliteration.

Early, late, or no shunt embolization in patients with cirrhosis- and portosystemic shunt-related hepatic encephalopathy

BACKGROUND

Portosystemic shunts (PSS) are associated with recurrent or persistent hepatic encephalopathy (HE), severe portal hypertensive (PHT) complications, and poor survival in cirrhosis patients. Shunt embolization improves HE in patients with recurrent or persistent HE. The role of early shunt embolization (ESE) in comparison with no and late SE (LSE) in cirrhosis patients with PSS and associated clinical outcomes are not studied.

METHODS

ESE was defined as occlusion of PSS in patients with the first episode of spontaneous HE, while LSE was that when performed in patients with recurrent/persistent PSS-related HE. We retrospectively analyzed (November 2016 to March 2019) clinical outcomes, liver disease severity, and survival between patients undergoing ESE (n = 22) vs. LSE (n = 23) and compared ESE with matched historical controls (n = 22) not undergoing shunt embolization, followed-up for 18 months.

RESULTS

Males predominated, and the lienorenal type of shunt was the most frequent. Significantly larger and multiple shunts were noted in the LSE group. Arterial ammonia, total bilirubin, and Child-Pugh scores were significantly higher at baseline in the LSE group. Post-procedure length of stay in the intensive unit (mean 0.6 vs. 2.1 days; p = 0.04), infections (31.8% vs. 66.7% beyond 100 days; p = 0.02), recurrence of HE in first 9 months (4.5% vs. 28.6%; p = 0.03), and liver- and PHT-related clinical events beyond 10 months were significantly higher in LSE compared with those in the ESE group respectively. HE beyond 10 months was comparable between both the groups. 18.2% died in ESE while 60.87% died in the LSE group (p = 0.002). Compared with patients on only standard medical care, the occurrence of ascites, variceal bleeding, recurrence of HE, and portal vein thrombosis were significantly lower in those undergoing ESE, even though differences in survival were not significant.

CONCLUSIONS

Our study demonstrates the benefits of ESE of large PSS in patients with cirrhosis, probably by improving survival through a reduction in liver and PHT events that warrant validation through prospective randomized controlled multicenter trials.

Plug-Assisted Retrograde Transvenous Obliteration (PARTO): Anatomical Factors Determining Procedure Outcome

PURPOSE

To study various anatomical factors determining procedure success versus failure for plug-assisted retrograde transvenous obliteration (PARTO) of gastro-lieno-renal shunt.

MATERIALS AND METHODS

A retrospective review of 50 patients (M:F-37:13; mean age 58.4yrs) who were planned for PARTO of gastro-lieno-renal shunt from July 2017 to July 2019 was done. Anatomical factors [shunt diameter, shunt angle, shunt orientation, left renal vein (LRV) size/calibre and distance of shunt from renal vein-IVC confluence] were analysed on a pre-procedure CT. Statistical analysis of the data was done to assess the relationship between these factors and technical success/failure.

RESULTS

PARTO was successfully performed in 82% (n = 41). Analysis of anatomical factors showed that aneurysmal dilatation of the LRV, extreme acute/obtuse angulation and extreme antero-posterior orientation of the shunt in relation to the LRV was associated with higher probability of technical failure of PARTO. Minimum/maximum and entry point shunt diameter was not associated with procedure outcome. It was also noted that an increased distance of the shunt from the renal vein-IVC confluence favoured trans-jugular over trans-femoral venous access for PARTO.

CONCLUSION

Knowledge of various anatomical factors of gastro-lieno-renal shunt may help in deciding the access route for PARTO and may determine technical success/failure. Alternate methods like BRTO or coil-assisted obliteration (CARTO) or anterograde obliteration of the shunt via trans-hepatic/splenic route might be needed in such circumstances.

ACR Appropriateness Criteria® Radiologic Management of Gastric Varices

Hemorrhage, resulting from gastric varies, can be challenging to treat, given the various precipitating etiologies. A wide variety of treatment options exist for managing the diverse range of the underlying disease processes. While cirrhosis is the most common cause for gastric variceal bleeding, occlusion of the portal or splenic vein in noncirrhotic states results in a markedly different treatment paradigm. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Spontaneous porto-systemic shunts in liver cirrhosis: Clinical and therapeutical aspects

Spontaneous porto-systemic shunts (SPSS) are frequent in liver cirrhosis and their prevalence increases as liver function deteriorates, probably as a consequence of worsening portal hypertension, but without achieving an effective protection against cirrhosis' complications. Several types of SPSS have been described in the literature, each one associated with different clinical manifestations. In particular, recurrent or persistent hepatic encephalopathy is more frequent in patients with splenorenal shunt, while the presence of gastric varices and consequently the incidence of variceal bleeding is more common in gastrorenal shunt. In the advanced stage, the presence of large SPSS can lead to the so called “portosystemic shunt syndrome”, characterized by a progressive deterioration of hepatic function, hepatic encephalopathy and, sometimes, portal vein thrombosis. The detection of SPSS in patients with liver cirrhosis is recommended in order to prevent or treat recurrent hepatic encephalopathy or variceal bleeding.

Management Options for Gastric Variceal Hemorrhage

Importance

Varices are one of the main clinical manifestations of cirrhosis and portal hypertension. Gastric varices are less common than esophageal varices but are often associated with poorer prognosis, mainly because of their higher propensity to bleed.

Observations

Currently, treatments used to control and manage gastric variceal bleeding include β-blockers, endoscopic injection sclerotherapy, endoscopic variceal ligation, endoscopic variceal obturation, shunt surgery, transjugular intrahepatic portosystemic shunts, balloon-occluded retrograde transvenous obliteration (BRTO), and modified BRTO. In the past few decades, Western (United States and Europe) interventional radiologists have preferred transjugular intrahepatic portosystemic shunts that aim to decompress the liver and reduce portal pressure. Conversely, Eastern radiologists (Japan and South Korea) have preferred BRTO that directly targets the gastric varices. Over the past 20 years, BRTO has evolved and procedure-related risks have decreased. Owing to its safety and efficiency in treating gastric varices, BRTO is now starting to gain popularity among Western interventional radiologists. In this review, we present a comprehensive literature review of current and emerging management options, including BRTO and modified BRTO, for the treatment of gastric varices in the setting of cirrhosis and portal hypertension.

Conclusions and Relevance

Balloon-occluded retrograde transvenous obliteration has emerged as a safe and effective alternative treatment option for gastric variceal hemorrhage. A proper training, evidence-based consensus and guideline, thorough preprocedural and postprocedural evaluation, and a multidisciplinary team approach with BRTO and modified BRTO are strongly recommended to ensure best patient care.

Utility of low-dose gelatin sponge particles and 5% ethanolamine oleate iopamidol mixture in retrograde transvenous obliteration (GERTO) for gastric varices

OBJECTIVE

To determine the utility of low-dose gelatin sponge particles and 5% ethanolamine oleate iopamidol (EOI) mixture in retrograde transvenous obliteration (GERTO) for gastric varices (GV).

METHODS

57 consecutive patients who underwent balloon-occluded retrograde transvenous obliteration (B-RTO) for GV were divided into three groups with Hirota's grade by balloon-occluded retrograde transvenous venography. Hirota's Grade 1 patients were assigned to G1 group and underwent treatment with 5% EOI. Grade ≥ 2 patients prior to August 2015 were G ≥ 2 group treated with 5% EOI, and those treated thereafter were GERTO group. The amount of EOI used per unit GV volume (EOI/GV ratio), the times to embolization and recurrence rate of GV were evaluated.

RESULTS

The EOI/GV ratio was 0.66 ± 0.19 in G1, 1.5 ± 0.8 in G ≥ 2, and 0.58 ± 0.23 in GERTO (G ≥ 2 vs GERTO, p < 0.0001). The times to embolization were 26.5 ± 10.5 min for G1, 39.2 ± 26.8 for G ≥ 2, and 21.4 ± 9.4 for GERTO (G ≥ 2 vs GERTO, p = 0.005). The recurrence rate was not significantly different in any of the groups.

CONCLUSION

GERTO was performed in lower amount of sclerosants and in less time compared to conventional B-RTO in Hirota's grade ≥2.

ADVANCES IN KNOWLEDGE

Feasibility of low-dose gelatin sponge particles and 5% EOI mixture as sclerosants for GV.

Endoscopic Therapy and Radiologic Intervention of Acute Gastroesophageal Variceal Bleeding

Acute gastroesophageal variceal hemorrhage is a dreaded complication in patients with liver cirrhosis. Endoscopic therapy and radiologic intervention for gastroesophageal bleeding have rapidly developed in the recent decades. Endoscopic treatment is initially performed to stop variceal hemorrhage. For the treatment of esophageal variceal bleeding, endoscopic variceal ligation (EVL) is considered the endoscopic treatment of choice. In cases of gastric variceal hemorrhage, the type of gastric varices (GVs) is important in deciding the strategy of endoscopic treatment. Endoscopic variceal obturation (EVO) is recommended for fundal variceal bleeding. For the management of gastroesophageal varix type 1 bleeding, both EVO and EVL are available treatment options; however, EVO is preferred over EVL. If endoscopic management fails to control variceal hemorrhage, radiologic interventional modalities could be considered. Transjugular intrahepatic portosystemic shunt is a good option for rescue treatment in refractory variceal bleeding. In cases of refractory hemorrhage of GVs in patients with a gastrorenal shunt, balloon-occluded retrograde transvenous obliteration could be considered as a salvage treatment.

Balloon Retrograde Transvenous Obliteration Versus Endoscopic Cyanoacrylate in Bleeding Gastric Varices: Comparison of Rebleeding and Mortality with Extended Follow-up

PURPOSE

To assess short- and long-term mortality and rebleeding with endoscopic cyanoacrylate (EC) versus balloon-occluded retrograde transvenous obliteration (BRTO).

MATERIALS AND METHODS

A retrospective cohort comparison was conducted of 90 EC patients and 71 BRTO patients from 1997 through 2015 with portal hypertension who presented due to endoscopically confirmed bleeding cardiofundal gastric varices. Patients underwent either endoscopic intra-varix injection of 4-carbon-n-butyl-2-cyanoacrylate or sclerosis with sodium tetradecyl sulfate with balloon occlusion for primary variceal treatment.

RESULTS

Seventy-one BRTO patients and 90 EC patients, of whom 89% had cirrhosis and 35% were women, were included, with a respective average Model for End-Stage Liver Disease (MELD) score of 13.4 and 14.4, respectively. Mortality at 6 weeks was 14.4% for EC patients and 13.1% for BRTO patients (Kaplan-Meier/Wilcoxon, P = .85). No long-term mortality difference was observed (Cox hazard ratio [HR] = 0.89, P = .64). Also, 5.1% of EC patients and 3.5% of BRTO patients (Kaplan-Meier/Wilcoxon, P = .62) rebled at 6 weeks, but at 1 year, 22.0% of EC patients and 3.5% of BRTO patients had rebled (Kaplan-Meier/Wilcoxon, P < .01). Lower rates of long-term rebleeding were found with BRTO (Cox HR = 0.25, P = .03). No difference was seen in the rate of new portal hypertensive complications (Cox HR = 1.21, P = .464). However, 16/71 patients who underwent BRTO had simultaneous transjugular intrahepatic portosystemic shunt. Age, sex, MELD score, and presence of cirrhosis were the primary predictors of mortality. One death in the EC group and 5 deaths in the BRTO group were deemed to be procedurally related (chi-square, P = .088).

CONCLUSIONS

BRTO is associated with a lower rate of rebleeding but no change in mortality.

Role of Interventional Radiology in Complications of Portal Hypertension

Portal hypertension, a consequence of end-stage liver disease and liver cirrhosis can lead to significant morbidity and mortality for patients through abnormal fluid accumulation as well as the formation of portosystemic shunts and varices. Treatment of the sequelae of portal hypertension can be achieved through endovascular management by referral to an interventional radiologist on an outpatient or emergent basis as required. Current techniques include the placement of peritoneovenous shunts and tunneled peritoneal drains, the creation of transjugular intrahepatic portosystemic shunts, or the obliteration of shunts via balloon-occluded retrograde transvenous obliteration (BRTO). In addition, newer procedural techniques utilizing vascular plugs and coils have reduced risks of the traditional BRTO procedure. Modified-BRTO procedures, known as plug-assisted and coil-assisted retrograde transvenous obliteration (PARTO and CARTO, respectively) have become the standard of care at many institutions for the treatment of gastric varices and portosystemic shunt-induced hepatic encephalopathy. This review examines the most recent literature of the management of portal hypertension by interventional radiologists, evaluating treatment options as well as the clinical and technical outcomes of TIPS, peritoneovenous shunts, tunneled peritoneal drains, BRTOs, and modified-BRTOs as well as future directions in the development of procedural techniques.

Recent development of balloon-occluded retrograde transvenous obliteration

Gastric varices (GVs) are a major complication of portal hypertension in patients with liver cirrhosis. The mortality rate associated with the bleeding from GVs is not low. Balloon-occluded retrograde transvenous obliteration (BRTO) was first introduced by Kanagawa et al. as a treatment for isolated GVs in 1994. It has been performed most frequently in Asia, especially in Japan. Ethanolamine oleate was the original sclerosant used in the therapy. Since the late 2000s, BRTO using sodium tetradecyl sulfate foam or polidocanol foam as a sclerosant has been performed in many countries other than Japan. Then, early in the 2010s, modified BRTO techniques including vascular plug-assisted retrograde transvenous obliteration and coil-assisted retrograde transvenous obliteration were developed as an alternative treatment for GVs. This article provides a historical overview of BRTO using various sclerosants and modified BRTO techniques, such as plug-assisted retrograde transvenous obliteration and coil-assisted retrograde transvenous obliteration.

Hepatic encephalopathy 2018: A clinical practice guideline by the Italian Association for the Study of the Liver (AISF)

Hepatic encephalopathy (HE) is a common, worrisome and sometimes difficult to manage complication of end-stage liver disease. HE is often recurrent, requiring multiple hospital admissions. It can have serious implications in terms of a patient's ability to perform complex tasks (for example driving), their earning capacity, their social and family roles. This guideline reviews current knowledge on HE definition, pathophysiology, diagnosis and treatment, both by general principles and by way of a summary of available drugs and treatment strategies. The quality of the published, pertinent evidence is graded, and practical recommendations are made. Where possible, these are placed within the Italian health service context, with reference to local diagnosis and management experience.

Radiological Intervention for Shunt Related Encephalopathy

Hepatic Encephalopathy (HE) is a neuropsychiatric syndrome that occurs in up to 30% of patients with cirrhosis. HE may be a consequence of pure liver failure, as in patients with fulminant hepatitis, or of the combination of liver failure and portal-systemic shunting, as in patients with liver cirrhosis. Several clinical and pathophysiologic observations suggest the importance of portal-systemic shunts in the development of HE. Episodes of HE are usually related to precipitating events, such as infections or gastrointestinal bleeding; a minority of cirrhotic patients experienced a chronic HE, refractory to standard medical treatment. This latter type of HE should be related to spontaneous or radiological (such as Transjugular Intrahepatic Portosystemic Shunt (TIPS)) portal systemic shunts, that could be restricted or occluded in patients with chronic HE. Both TIPS reduction and shunt occlusion are radiological procedures, safe and effective to ameliorate neurological symptoms in patients with refractory HE.

Evolution of Retrograde Transvenous Obliteration Techniques

Gastric variceal hemorrhage is a life-threatening complication of portal hypertension with a poorer prognosis compared with esophageal variceal hemorrhage. The presence of an infradiaphragmatic portosystemic shunt, often a gastrorenal shunt, allows for treatment with retrograde transvenous obliteration (RTO). RTO is an evolving treatment strategy, which includes balloon-assisted RTO, plug-assisted RTO, and coil-assisted RTO, for both gastric variceal hemorrhage and hepatic encephalopathy. RTO techniques are less invasive than transjugular intrahepatic portosystemic shunt creation, with the benefit of improved hepatic function, but at the expense of increased portal pressure. This article discusses the techniques of RTO, including patient eligibility, as well as technical and clinical outcomes, including adverse events.

Coil-Assisted Retrograde Transvenous Obliteration (CARTO): An Alternative Treatment Option for Refractory Hepatic Encephalopathy

BACKGROUND

Overt hepatic encephalopathy (OHE) is a serious complication of liver dysfunction, which is associated with severe morbidity/mortality and healthcare resource utilization. OHE can be medically refractory due to spontaneous portosystemic shunts (SPSSs) and therefore a new treatment option for these SPSSs is critical.

METHODS

This is a retrospective study of 43 patients with medically refractory OHE, who underwent CARTO (Coil-Assisted Retrograde Transvenous Obliteration) procedures between June 2012 and October 2016. The patient demographic characteristics, technical and clinical outcomes with an emphasis on HE improvement, and complications are reviewed and analyzed.

RESULTS

The overall clinical success rate was 91% with a significant HE improvement. Eighty-one percent of patients had clinically significant improvement from OHE and 67% of patients had complete resolution of their HE symptoms during our follow-up period of 893 ± 585 days (range 36-1881 days, median 755.0 days). The median WH score improved from 3 (range 2-4) pre-CARTO to 1 (range 0-4) post-CARTO (p < 0.001). The median ammonia level significantly decreased from 134.5 pre-CARTO to 70.0 post-CARTO (p < 0.001) in 3 days. The overall mean survival was 1465.5 days (95% CI of 1243.0 and 1688.0 days). Only three patients had recurrent HE symptoms. There were 39.6% minor complication rate including new or worsened ascites and esophageal varices, and only 2.3% major complication rate requiring additional treatment (one patient with bleeding esophageal varices requiring treatment). No procedure-related death is noted.

CONCLUSIONS

CARTO appears to be a safe and effective treatment option for refractory overt hepatic encephalopathy (OHE) due to spontaneous portosystemic shunts. CARTO could be an excellent addition to currently available treatment options for these patients.

Plug-Assisted Retrograde Transvenous Obliteration for the Treatment of Gastric Varices: The Role of Intra-Procedural Cone-Beam Computed Tomography

Objective

To investigate the technical and clinical outcomes of plug-assisted retrograde transvenous obliteration (PARTO) for the treatment of gastric varices (GV) and to evaluate the role of intra-procedural cone-beam computed tomography (CBCT) performed during PARTO to confirm its technical success.

Materials and Methods

From January 2016 to December 2016, 17 patients with GV who had undergone PARTO were retrospectively evaluated. When the proximal part of the afferent vein was identified on a fluoroscopy, non-contrast CBCT images were obtained. In patients with incomplete embolization of GV, an additional injection of gelatin sponges was performed. Follow-up data from contrast-enhanced CT and upper intestinal endoscopy, as well as clinical and laboratory data were collected.

Results

Plug-assisted retrograde transvenous obliteration procedures were technically successful in all 17 patients. Complete embolization of GV was detected on CBCT images in 15 patients; whereas, incomplete embolization was detected in two. Complete embolization of GV was then achieved after an additional injection of gelatin sponges in these two patients as demonstrated on the 2nd CBCT image. The mean follow-up period after PARTO was 193 days (range, 73–383 days). A follow-up CT obtained 2–4 months after PARTO demonstrated marked shrinkage or complete obliteration of GV and portosystemic shunts in all 17 patients. There were no cases of variceal bleeding during the follow-up.

Conclusion

Plug-assisted retrograde transvenous obliteration is technically and clinically effective for the treatment of GV. In addition, intra-procedural CBCT can be an adjunct tool to fluoroscopy, because it can provide an immediate and accurate evaluation of the technical success of PARTO.

Modified Balloon-Occluded Retrograde Transvenous Obliteration (BRTO) Techniques for the Treatment of Gastric Varices: Vascular Plug-Assisted Retrograde Transvenous Obliteration (PARTO)/Coil-Assisted Retrograde Transvenous Obliteration (CARTO)/Balloon-Occluded Antegrade Transvenous Obliteration (BATO)

Gastric varices in the setting of portal hypertension occur less frequently than esophageal varices but occur at lower portal pressures and are associated with more massive bleeding events and higher mortality rate. Balloon-occluded retrograde transvenous obliteration (BRTO) of gastric varices has been well documented as an effective therapy for portal hypertensive gastric varices. However, BRTO requires lengthy, higher-level post-procedural monitoring and can have complications related to balloon rupture and adverse effects of sclerosing agents. Several modified BRTO techniques have been developed including vascular plug-assisted retrograde transvenous obliteration, coil-assisted retrograde transvenous obliteration, and balloon-occluded antegrade transvenous obliteration. This article provides an overview of various modified BRTO techniques.

Prevention and management of gastroesophageal varices

Bleeding from gastroesophageal varices is a serious complication in patients with liver cirrhosis and portal hypertension. Although there has been significance improvement in the prognosis of variceal bleeding with advancement in diagnostic and therapeutic modalities for its management, mortality rate still remains high. Therefore, appropriate prevention and rapid, effective management of bleeding from gastroesophageal varices is very important. Recently, various studies about management of gastoesophageal varices, including prevention of development and aggravation of varices, prevention of first variceal bleeding, management of acute variceal bleeding, and prevention of variceal rebleeding, have been published. The present article reviews published articles and practice guidelines to present the most optimal management of patients with gastroesophageal varices.

Percutaneous Transparaumbilical Embolization of Spontaneous Portosystemic Shunts for the Treatment of Hepatic Encephalopathy

The medical records of 7 patients who underwent percutaneous transparaumbilical embolization of spontaneous portosystemic shunts for treatment of hepatic encephalopathy (HE) were retrospectively reviewed. Technical success was achieved in 100% (7/7) of patients. Four patients had complete resolution and 3 had improvement of signs and symptoms of HE within 3 days after the procedure for a clinical success rate of 100% (7/7). New-onset esophageal varices, a major complication, occurred in 1 patient. No other major complications were encountered. HE recurred in 71.4% (5/7) of patients during a median follow-up period of 43 months (range, 4-111 months).

Retrograde-Antegrade Accelerated Trap Obliteration: A Modified Approach to Transvenous Eradication of Gastric Varices

This series presents a hybrid technique for obliteration of gastric varices (GVs) termed retrograde-antegrade accelerated trap obliteration that employs sclerosant agent instillation under concurrent inflow and outflow vessel occlusion with coils or plugs. Six patients (mean age, 56 y) with GVs were treated in 2014 and 2015. Technical success rate was 100%. Five patients completed 30-day follow-up. There were no procedure-related complications, and clinical success rate was 100%, with no bleeding recurrence over a mean follow-up of 298 days ± 178. GV obliteration rate was 100% (n = 4) at a mean of 157 days ± 158. This limited experience suggests that the described technique represents a viable approach to GV obliteration.

Probiotics for Gastrointestinal Conditions: A Summary of the Evidence

Probiotics contain microorganisms, most of which are bacteria similar to the beneficial bacteria that occur naturally in the human gut. Probiotics have been widely studied in a variety of gastrointestinal diseases. The most-studied species include Lactobacillus, Bifidobacterium, and Saccharomyces. However, a lack of clear guidelines on when to use probiotics and the most effective probiotic for different gastrointestinal conditions may be confusing for family physicians and their patients. Probiotics have an important role in the maintenance of immunologic equilibrium in the gastrointestinal tract through the direct interaction with immune cells. Probiotic effectiveness can be species-, dose-, and disease-specific, and the duration of therapy depends on the clinical indication. There is high-quality evidence that probiotics are effective for acute infectious diarrhea, antibiotic-associated diarrhea, Clostridium difficile- associated diarrhea, hepatic encephalopathy, ulcerative colitis, irritable bowel syndrome, functional gastrointestinal disorders, and necrotizing enterocolitis. Conversely, there is evidence that probiotics are not effective for acute pancreatitis and Crohn disease. Probiotics are safe for infants, children, adults, and older patients, but caution is advised in immunologically vulnerable populations.