Hepatic artery stenosis following liver transplantation: significance of the tardus parvus waveform and the role of microbubble contrast media in the detection of a focal stenosis

The Sonographic Stenosis Index: A New Specific Quantitative Measure of Transplant Hepatic Arterial Stenosis

OBJECTIVES

This study evaluates the sensitivity and specificity of stenosis index (SI), which accounts for the entire spectral Doppler waveform, to detect significant transplant hepatic arterial stenosis.

MATERIALS AND METHODS

In this institutional review board-approved, HIPAA compliant study, we retrospectively analyzed 69 patients who had catheter angiography for suspected transplant hepatic arterial stenosis (THAS) between January 2006 and December 2010; all patients had Doppler ultrasound within 30 days before angiography. Patients with angiographic stenosis requiring intervention were considered positive for THAS. Stenosis index was calculated from each patient's spectral Doppler ultrasound images by obtaining the ratio of the area under the high-frequency signal to low-frequency signal in the spectral Doppler. Resistive index (RI) and pulsatility index (PI) were also calculated. Receiver operator curve analysis was performed and the area under the curve (AUC) was compared among the three metrics.

RESULTS

Forty-eight of 69 patients had THAS by angiography requiring intervention; 21patients had no angiographic evidence of THAS. SI was significantly different (P < .001) between patients with THAS (SI = 1.04 ± 0.20) and those without THAS (SI = 1.39 ± 0.30). Stenosis index had an AUC of 0.86 for detecting THAS, which was significantly higher than that from RI (AUC = 0.68, P = .038 for the comparison) and PI (AUC = 0.70, P = .029). For SI < 1.35, the sensitivity for THAS was 94% and specificity was 52%. For RI < 0.5, the sensitivity was 96% and the specificity was 29%.

CONCLUSIONS

Stenosis index is more accurate than the resistive index and the pulsatility index for detecting transplant hepatic artery stenosis.

Vascular complications after adult living donor liver transplantation: Evaluation with ultrasonography

Living donor liver transplantation (LDLT) has been widely used to treat end-stage liver disease with improvement in surgical technology and the application of new immunosuppressants. Vascular complications after liver transplantation remain a major threat to the survival of recipients. LDLT recipients are more likely to develop vascular complications because of their complex vascular reconstruction and the slender vessels. Early diagnosis and treatment are critical for the survival of graft and recipients. As a non-invasive, cost-effective and non-radioactive method with bedside availability, conventional gray-scale and Doppler ultrasonography play important roles in identifying vascular complications in the early postoperative period and during the follow-up. Recently, with the detailed vascular tracing and perfusion visualization, contrast-enhanced ultrasound (CEUS) has significantly improved the diagnosis of postoperative vascular complications. This review focuses on the role of conventional gray-scale ultrasound, Doppler ultrasound and CEUS for early diagnosis of vascular complications after adult LDLT.

Hepatic artery stenosis after liver transplantation: is endovascular treatment always necessary?

Hepatic artery stenosis (HAS) is thought to predispose patients to biliary complications secondary to ischemic injury. Despite this, the clinical significance of HAS remains poorly defined. The aims of this study were to determine the prevalence and outcomes of HAS and to define which patients might benefit from endovascular treatment. From a prospective database of 662 adult patients undergoing liver transplantation between 2000 and 2011, we identified 54 patients who developed HAS. HAS was defined as any stenosis > 70% that was seen during multidetector computed tomographic angiography (MDCTA) or digital subtraction angiography. The benefit of endovascular therapy was evaluated with propensity score matching. New biliary complications occurred in 17 patients (31.4%), and 23 of the 54 study patients with HAS received endovascular treatment. Among the propensity score-matched patients, the biliary stricture-free survival time was significantly longer for those who received endovascular therapy (P = 0.03). An incidental diagnosis (P = 0.07) and a time from transplantation > 6 months (P = 0.021) were associated with a reduced risk of developing biliary stricture. Patients with symptomatic HAS who received treatment had better biliary stricture-free survival than patients who were treated conservatively, although no significant difference was recorded (P = 0.11). No patient with asymptomatic HAS and normal liver function tests developed biliary strictures. In conclusion, HAS intervention was associated with improved biliary stricture-free survival. In patients with late-onset HAS (≥6 months) and asymptomatic patients, endovascular treatment is not warranted.

Hepatic artery reconstruction in living donor liver transplantation: risk factor analysis of complication and a role of MDCT scan for detecting anastomotic stricture

BACKGROUND

In partial liver transplantation, reconstruction of the hepatic artery is technically highly demanding and the incidence of arterial complications is high. We attempted to identify the risk factors for anastomotic complications after hepatic artery reconstruction and examined the role of multidetector-row computed tomography (MDCT) in the evaluation of the reconstructed hepatic artery in liver transplant recipients.

METHODS

A total of 109 adult-to-adult living donor liver transplantations (LDLT) were performed at our institute between 1999 and July 2011. Hepatic artery reconstruction was performed under a surgical microscope (MS group, n = 84), until we began to adopt surgical loupes (4.5×) for arterial reconstructions in all cases after January 2009 (SL group, n = 25). A dynamic MDCT study was prospectively carried out on postoperative days 7, 14, and 28, and at postoperative month 3, 6, and 12 after April 2005 (n = 60).

RESULTS

There were no cases of hepatic artery thrombosis and six cases (5.5 %) of interventional radiology-confirmed hepatic artery stenosis (HAS). Risk factor analysis for HAS showed that ABO-incompatible LDLT was associated with HAS. Use of surgical loupes provided superior results as compared to anastomosis under a surgical microscope, and it also provided the advantage of reduced operative time. The MDCT procedure was useful for detecting HAS; however, the false positive rate was relatively high until 3 months after the LDLT (100 % sensitivity and 72.8 % specificity at 3 months).

CONCLUSIONS

Hepatic arterial anastomosis using surgical loupes tended to be time-saving and to yield similar or better results than traditional microscope-anastomosis. The use of MDCT aided the diagnosis of HAS, although the substantial false positive rate should be borne in mind in clinical practice.

Radiologic assessment of hepatobiliary surgical complications

The complexity of hepatobiliary procedures continues to evolve at a rapid rate, with an increasing number of living donor liver transplants and extensive cancer resections being performed. The associated complications are a significant cause of morbidity and mortality, and are often complex injuries, involving both vascular and biliary structures. In this paper we describe the complications associated with laparoscopic cholecystectomy, liver transplant surgery, and hepatic resection. Focus is on the classical imaging appearances, imaging modality options, and varying management strategies for these injuries, to show how the radiologist's role is vital in ensuring the correct diagnosis is made and the appropriate treatment is instigated.

Role of contrast-enhanced ultrasound in decision support for diagnosis and treatment of hepatic artery thrombosis after liver transplantation

OBJECTIVE

To assess role of contrast-enhanced ultrasound (CEUS) in decision support for diagnosis and treatment of hepatic artery thrombosis (HAT) after liver transplantation.

MATERIALS AND METHODS

Between January 2005 and January 2011, 605 patients underwent liver transplantation in our medical center. All the liver transplant recipients received Doppler ultrasound scanning and CEUS examination was performed in 45 patients with suspected HAT on Doppler ultrasound. Sensitivity, specificity, accuracy, positive predict value and negative predictive value of CEUS in diagnosing HAT were determined based on the results from angiography, surgery and clinical follow-up.

RESULTS

Fourteen HATs, including one late HAT, were diagnosed by CEUS. Twelve HAT cases were confirmed by angiographic and/or surgical findings, while the late HAT and other 31 patients with negative CEUS finding were confirmed by the clinical follow-up. There was a false positive HAT diagnosed by CEUS in which angiography revealed a patent hepatic artery. The sensitivity, specificity, accuracy, positive predict value and negative predictive value of CEUS in diagnosing HAT were 100%, 96.9%, 97.8%, 92.9% and 100%, respectively. In our series of 605 liver transplants, the incidence and mortality of HAT was 2.2% (13/605) and 53.8% (7/13), respectively.

CONCLUSIONS

Our study demonstrates the important role of CEUS in decision support for diagnosis and treatment of HAT after liver transplantation. When HAT is suspected by Doppler ultrasound, CEUS shall immediately be performed to elucidate its nature. A negative CEUS finding shall avoid invasive angiography. Such as, CEUS may alter the clinical workflow on HAT detection after liver transplantation.

Hepatic arterial stenosis assessed with doppler US after liver transplantation: frequent false-positive diagnoses with tardus parvus waveform and value of adding optimal peak systolic velocity cutoff

PURPOSE

To evaluate the utility of the tardus parvus waveform of the hepatic artery at Doppler ultrasonography (US) in the diagnosis of hepatic arterial stenosis in liver transplant (LT) recipients and determine whether the accuracy of such a diagnosis is enhanced by including an optimal peak systolic velocity (PSV) cutoff.

MATERIALS AND METHODS

This retrospective study was institutional review board approved; the requirement for informed consent was waived. The authors identified 361 LT recipients (267 male, 94 female) who underwent Doppler US and either computed tomography (CT) or angiography, with an interval between these examinations of less than 1 week. At Doppler US, tardus parvus pattern was defined as a waveform with a resistive index (RI) of less than 0.5 and a systolic acceleration time longer than 0.08 second. At CT or angiography, patients were assigned to the hepatic arterial stenosis (≥50% vessel narrowing) or nonstenosis group. The capability of the tardus parvus pattern to facilitate the diagnosis of hepatic arterial stenosis was calculated. The difference in PSV between the true- and false-positive tardus parvus patterns was evaluated. Receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff PSV for diagnosing hepatic arterial stenosis. The capability of the tardus parvus pattern and an optimal PSV cutoff in the diagnosis of hepatic arterial stenosis was determined.

RESULTS

Sixty transplant recipients had the tardus parvus pattern at Doppler US. The sensitivity, specificity, and positive predictive value (PPV) of the tardus parvus pattern were 72% (23 of 32 LT recipients), 88.8% (292 of 329 LT recipients), and 38% (23 of 60 LT recipients), respectively. The false-positive rate was 11.2% (37 of 329 LT recipients). ROC analysis revealed an optimal PSV cutoff of less than or equal to 48 cm/sec for diagnosing hepatic arterial stenosis. The combination of the tardus parvus pattern and a PSV cutoff of less than or equal to 48 cm/sec improved specificity to 99.1% (326 of 329 LT recipients) and the PPV to 88% (22 of 25 LT recipients), thereby reducing the false-positive rate to 1% (three of 329 LT recipients) while slightly decreasing the sensitivity to 69% (22 of 32 LT recipients).

CONCLUSION

Use of the tardus parvus waveform of the hepatic artery resulted in a low PPV and a high false-positive rate. However, the combination of the tardus parvus pattern and an optimal PSV cutoff greatly improved the PPV and reduced the false-positive rate in the diagnosis of hepatic arterial stenosis.

Doppler ultrasound findings in the hepatic artery shortly after liver transplantation

OBJECTIVE

The purpose of this article is to describe the Doppler waveform findings in the hepatic artery in the early posttransplantation period, both in the absence and presence of arterial complications.

CONCLUSION

The presence of transient high-resistance Doppler waveforms in normal hepatic arteries is a common finding after grafting. Hepatic artery thrombosis and stenosis, and arterial steal syndromes can be diagnosed by Doppler in the early liver transplantation period.

The immunopathology of human biliary cell epithelium

Bile ducts lined with biliary epithelial cells, or cholangiocytes, are the main components of the biliary system in liver. Cholangiocytes participate in the production and transport of bile substances, as well as participate in immune responses. Cholangiocytes protect against pathogens by expressing toll-like receptors and anti-microbial peptides; act as antigen-presenting cells by expressing human leukocyte antigen molecules and costimulatory molecules; recruit leukocytes to the target site by expressing adhesion molecules, cytokines, and chemokines; and induce apoptosis of leukocytes to limit the immune responses. Several cholangiopathies result from dysfunctions of the biliary system. They can broadly be divided into autoimmune, genetic, infectious, drug, and ischemic-injury-induced categories. The pathogenesis of many of these cholangiopathies is unclear and treatment is limited. Further understanding of the complexity of the biliary system is critical for medical advancements in this field.

Routine intraoperative Doppler sonography in the evaluation of complications after living-related donor liver transplantation

PURPOSE

To determine whether quantitative and qualitative analysis of intraoperative Doppler sonography data are predictive of vascular complications after living-related donor liver transplantation.

METHODS

Intraoperative sonograms of 81 transplanted livers (right lobe in 61 patients, left lobe in 20 patients) were analyzed for the presence of blood flow, resistance index, systolic acceleration time (SAT), peak systolic velocity, and morphologic characteristics of spectral waveform of the hepatic artery. Peak velocity and spectral waveforms of portal and hepatic veins were also analyzed. Intraoperative sonography results were compared with information obtained with multidetector-row CT (MDCT) angiography or conventional angiography. The time interval between operation and angiography ranged from 1 to 23 days (mean, 8.5 days).

RESULTS

Hepatic artery stenosis (HAS) was identified in 20 patients via MDCT angiography, conventional angiography, or both. The Doppler parameters found helpful for predicting HAS were tardus-parvus pattern and delayed SAT. The sensitivity, specificity, and negative predictive value (NPV) were 60.0%, 73.7%, and 84.9%, respectively, for tardus-parvus pattern and 40.0%, 83.6%, and 80.9%, respectively, for delayed SAT. Peak velocities of the portal and hepatic veins were not reliable indicators of vascular complication. Loss of triphasity of the hepatic vein had a 98.4% NPV for venous obstruction.

CONCLUSIONS

Delayed SAT of the hepatic artery and loss of triphasity of the hepatic vein had a >80% for specificity for predicting vascular complications. Tardus-parvus pattern, delayed SAT of the hepatic artery, and loss of triphasity of the hepatic vein showed an acceptable NPV for identifying vascular complications.

Contrast-enhanced ultrasound with SonoVue in the evaluation of postoperative complications in pediatric liver transplant recipients

PURPOSE

To evaluate the utility of contrast-enhanced sonography in the study of pediatric liver transplant recipients and its potential impact in reducing the need for invasive diagnostic procedures.

MATERIALS AND METHODS

From October 2002 to December 2003 we performed routine color Doppler ultrasound and contrast-enhanced ultrasound studies on 30 pediatric patients who had undergone liver transplantation. Findings indicative of complications were confirmed with invasive studies (angiography, computed tomography, and PTC).

RESULTS

Contrast-enhanced sonography correctly identified four of the five cases of hepatic artery thrombosis and all those involving the portal (n = 6) and hepatic vein (n = 3) thrombosis. It failed to identify one case of hepatic artery thrombosis characterized by collateral circulation arising from the phrenic artery and the single case of hepatic artery stenosis. The latter was more evident on color Doppler, which revealed a typical tardus parvus waveform. The use of contrast offered no significant advantages in the study of biliary complications although it did provide better visualization of bile leaks.

CONCLUSIONS

Contrast-enhanced sonography improves diagnostic confidence and reduces the need for more invasive imaging studies in the postoperative follow-up of pediatric liver transplant recipients.

Doppler ultrasonographic findings on hepatic arterial vasospasm early after liver transplantation

OBJECTIVE

Hepatic arterial vasospasm has not been well recognized clinically as a post-liver transplant vascular complication because of the lack of sufficient data and diagnostic standards. The goal of this study was to provide new evidence and a diagnostic model for the clinical appreciation of hepatic arterial vasospasm and evaluate the role of ultrasonography in the diagnostic process.

METHODS

Nine post-orthotopic liver transplant cases were retrospectively reviewed. Multiple clinical measurements were analyzed. Routine Doppler ultrasonography was performed within 24 hours, and additional ultrasonographic examinations were conducted as indicated. Each of the 9 patients was given a single 10 mg dose of nifedipine sublingually and monitored by ultrasonography when vasospasm was suspected on the basis of the Doppler ultrasonographic results.

RESULTS

Doppler ultrasonography showed high-resistance hepatic arterial flow with absence of antegrade flow and even reversal of flow during diastole both extrahepatically and intrahepatically in all cases. Ten to 45 minutes after administration of the vasodilator, antegrade diastolic flow was observed along the course of the main hepatic artery and its intrahepatic branches with the resistive indices decreasing on average from 1.0 to 0.76. In addition, the peak systolic velocities increased from 57 cm/s before nifedipine administration to 77 cm/s after administration.

CONCLUSIONS

High-resistance hepatic arterial flow (resistive index = 1) early after liver transplantation is indicative of hepatic arterial vasospasm if it responds to vasodilators. Doppler ultrasonography is a useful tool for the diagnosis of this vascular complication.

Diagnostic efficacy of SonoVue®, a second generation contrast agent, in the assessment of extracranial carotid or peripheral arteries using colour and spectral Doppler ultrasound: a multicentre study

The purpose of this study was to demonstrate the improvement in diagnostic quality and diagnostic accuracy of SonoVue microbubble contrast-enhanced ultrasound (CE-US) versus unenhanced ultrasound imaging during the investigation of extracranial carotid or peripheral arteries. 82 patients with suspected extracranial carotid or peripheral arterial disease received four SonoVue doses (0.3 ml, 0.6 ml, 1.2 ml and 2.4 ml) with Doppler ultrasound performed before and following each dose. Diagnostic quality of the CE-US examinations was evaluated off-site for duration of clinically useful contrast enhancement, artefact effects and percentage of examinations converted from non-diagnostic to diagnostic. Accuracy, sensitivity and specificity were assessed as agreement of CE-US diagnosis evaluated by an independent panel of experts with reference standard modality. The median duration of clinically useful signal enhancement significantly increased with increasing SonoVue doses (p< or =0.002). At the dose of 2.4 ml of SonoVue, diagnostic quality evaluated as number of inconclusive examinations significantly improved, falling from 40.7% at baseline down to 5.1%. Furthermore, SonoVue significantly (p<0.01) increased the accuracy, sensitivity and specificity of assessment of disease compared with baseline ultrasound. SonoVue increases the diagnostic quality of Doppler images and improves the accuracy of both spectral and colour Doppler examinations of extracranial carotid or peripheral arterial disease.

Interventional Radiology in Liver Transplantation

Radiology is a key specialty within a liver transplant program. Interventional techniques not only contribute to graft and recipient survival but also allow appropriate patient selection and ensure that recipients with severe liver decompensation, hepatocellular carcinoma or portal hypertension are transplanted with the best chance of prolonged survival. Equally inappropriate selection for these techniques may adversely affect survival. Liver transplantation is a dynamic field of innovative surgical techniques with a requirement for interventional radiology to parallel these developments. This paper reviews the current practice within a major European center for adult and pediatric transplantation.

Contrast enhanced ultrasound in liver imaging

Ultrasound contrast agents were originally introduced to enhance the Doppler signals when detecting vessels with low velocity flow or when imaging conditions were sub-optimal. Contrast agents showed additional properties, it was discovered that a parenchymal enhancement phase in the liver followed the enhancement of the blood pool. Contrast agents have made ultrasound scanning more accurate in detection and characterization of focal hepatic lesions and the sensitivity is now comparable with CT and MRI scanning. Further, analysis of the transit time of contrast agent through the liver seems to give information on possible hepatic involvement, not only from focal lesions but also from diffuse benign parenchymal disease. The first ultrasound contrast agents were easily destroyed by the energy from the sound waves but newer agents have proved to last for longer time and hereby enable real-time scanning and make contrast enhancement suitable for interventional procedures such as biopsies and tissue ablation. Also, in monitoring the effect of tumour treatment contrast agents have been useful. A brief overview is given on some possible applications and on different techniques using ultrasound contrast agents in liver imaging. At present, the use of an ultrasound contrast agent that allows real-time scanning with low mechanical index is to be preferred.