Complications after endovascular treatment of hepatic artery stenosis after liver transplantation. J Vasc Surg. 2017;66:1488-1496. [PMID: 28697937 DOI: 10.1016/j.jvs.2017.04.062]

Safety and Effectiveness of Early Primary Stent Placement for Hepatic Artery Stenosis in Liver Transplant Recipients

PURPOSE

To evaluate the outcomes of early primary stent placement (within 30 days of liver transplantation) for hepatic artery stenosis (HAS).

MATERIALS AND METHODS

Patients who underwent liver transplantation between February 2001 and February 2024 were evaluated for HAS. Patients who underwent primary stent placement were selected and stratified based on the time from anastomosis to intervention. Early intervention was defined as primary stent placement within 30 days of surgical anastomosis. Kaplan-Meier analysis was performed for primary patency.

RESULTS

HAS occurred in 83 of 779 (11%) patients (median age, 55 years; interquartile range, 48-63 years; 27 [48%] women), with 56 patients meeting inclusion criteria. Stent placement was performed within 0-6 days of the anastomosis in 11 (20%), 7-14 days in 11 (20%), 15-30 days in 7 (12%), 31-70 days in 9 (16%), and >70 days in 18 (32%) patients. Technical success was 100%. Primary patency rates were 89%, 87%, and 87% at 1, 3, and 5 years, respectively. Primary assisted patency rates were 100% at 1, 3, and 5 years. Early interventions at 0-6 days, 7-14 days, and 15-30 days showed primary patency rates of 100%, 90%, and 86%, respectively, at 1 year (P = .58). There was no difference in primary patency between the early (<30 days) and late (>30 days) cohorts (P = .88). There was 1 Grade 4 adverse event. There were no cases of anastomotic rupture, hepatic artery dissection, or graft failure.

CONCLUSIONS

Hepatic artery stent placement within 30 days of liver transplantation is safe and technically successful with excellent long-term primary patency.

Hepatic artery stenosis following adult liver transplantation: evaluation of different endovascular treatment approaches

PURPOSE

To evaluate the efficacy and safety of hepatic artery interventions (HAI) versus extra-hepatic arterial interventions (EHAI) when managing clinically significant hepatic artery stenosis (HAS) after adult orthotopic liver transplantation.

MATERIALS AND METHODS

A single-center retrospective cohort analysis was conducted on liver transplant patients who underwent intervention for clinically significant HAS from September 2012 to September 2021. The HAI treatment arm included hepatic artery angioplasty and/or stent placement while the EHAI treatment arm comprised of non-hepatic visceral artery embolization. Primary outcomes included peri-procedural complications and 1-year liver-related deaths. Secondary outcomes included biliary ischemic events, longitudinal trends in liver enzymes and ultrasound parameters pre-and post-intervention.

RESULTS

The HAI arm included 21 procedures in 18 patients and the EHAI arm included 27 procedures in 22 patients. There were increased 1-year liver-related deaths (10% [2/21] vs 0% [0/27], p = 0.10) and complications (29% [6/21] vs 4% [1/27], p = 0.015) in the HAI group compared to the EHAI group. Both HAI and EHAI groups exhibited similar improvements in transaminitis including changes of ALT (-72 U/L vs -112.5 U/L, p = 0.60) and AST (-58 U/L vs -48 U/L, p = 0.56) at 1-month post-procedure. Both treatment arms demonstrated increases in post-procedural peak systolic velocity of the hepatic artery distal to the stenosis, while the HAI group also showed significant improvement in resistive indices following the intervention.

CONCLUSION

Direct hepatic artery interventions remain the definitive treatment for clinically significant hepatic artery stenosis; however, non-hepatic visceral artery embolization can be considered a safe alternative intervention in cases of unfavorable hepatic anatomy.

Transplant Hepatic Artery Complications

Hepatic artery complications can be divided into 2 different categories, nonocclusive and steno-occlusive disease. Steno-occlusive disease is a collective term that encompasses hepatic artery thrombosis, hepatic artery stenosis, and hepatic arterial kinks, while nonocclusive arterial disease encompasses less than 5% of complications and is a collective term used to describe arteriovenous fistulae, pseudoaneurysms, arterial rupture and nonocclusive hepatic artery hypoperfusion syndrome. This article details the angiographic techniques and definitions needed to accurately diagnose arterial transplant complications and describes the technical aspects and results of endoluminal management of these arterial complications. In addition, this article discusses the presentation, etiology and indications for treatment, including surgical management of these various complications.

Endovascular therapies for hepatic artery stenosis post liver transplantation

PURPOSE

To evaluate primary patency at 12 months after endovascular therapies in hepatic artery stenosis.

METHODS

A retrospective review of all endovascular interventions for hepatic artery stenosis (HAS) after liver transplantation that occurred between June 2013 and November 2020 was performed at a single institution in France. Follow up occurred from 1 month to 4 years (median 15 months). The treatment consisted of dilation with a balloon or stent. We analyzed short-term (technical success and complications) and long-term outcomes (liver function, arterial patency, graft survival at 12 months (GS), and reintervention). We also compared percutaneous balloon angioplasty (PBA) with stent placement. PBA alone was used if < 30% residual stenosis of the hepatic artery was achieved. Stenting was performed if there was greater than 30% residual stenosis and in the case of complications (dissection or rupture).

RESULTS

A total of 18 stenoses were suspected on the basis of routine surveillance duplex ultrasound imaging (peak systolic velocity > 200 cm/s, systolic accelerating time > 10 ms and resistive index < 0.5), all of which were confirmed by angio CT, but only 17 were confirmed by angiography. Seventeen patients were included (14 males, mean age 57 years; and three females, mean age 58 years). Interventions were performed in 17 cases (95%) with PBA only (5/17), stent only (5/17) or both (4/17). Immediate technical success was 100%. Major complications occurred in 1 of 17 cases (5.8%), consisting of target vessel dissection. The analysis of the three (groups PBA only, stent only or both) showed the same procedural success (100%), GS (100%) and normal liver function after the procedures but different rates of complications (20% vs. 0% vs. 0%), arterial patency at 12 months (60% vs. 80% vs. 85%) (p = 0.4), early stenosis (40% vs. 80% vs. 0%) or late stenosis (60% vs. 20% vs. 100%) and requirement for reintervention (40% vs. 20% vs. 14%) (p = 0.56).

CONCLUSION

This study suggests that PBA, stent, or both procedures show the same primary patency at 12 months. It is probably not a definitive answer, but these treatments are safe and effective for extending graft survival in the context of graft shortages.

Risk factors and management of hepatic artery stenosis post liver transplantation

BACKGROUND

Hepatic Artery Stenosis (HAS) after liver transplantation (LT), if untreated, can lead to hepatic artery thrombosis (HAT) that carries significant morbidity.

AIMS

To identify risk factors associated with HAS and determine if endovascular therapy (EVT) reduces the occurrence of HAT.

METHODS

This is a retrospective cohort study of adult LT patients between 2013 and 2018. The primary outcome was development of HAT, and secondary outcomes included graft failure and mortality. Logistic regression was used to ascertain the odds ratio of developing HAS. Outcomes between intervention types were compared with Fisher's-exact test.

RESULTS

The odds of HAS doubled in DCD-donor recipients (OR=2.27; P = 0.04) and transplants requiring vascular reconstruction for donor arterial variation (OR=2.19, P = 0.046). Of the 63 identified HAS patients, 44 underwent EVT, 7 with angioplasty alone, 37 combined with stenting. HAT was not significantly different in those who underwent angioplasty with or without stenting than conservative treatment (P = 0.71). However, compared to patients without HAS, patients with HAS had higher odds of biliary stricture and decreased graft and overall patient survival (log-rank P < 0.001 & P = 0.019, respectively).

CONCLUSION

HAS is significantly higher in DCD-graft recipients. EVT was not associated with reduction in HAT progression. HAS has poor graft and overall survival.

Neuroform EZ Stents for Hepatic Artery Stenosis After Liver Transplantation: A Single-Center Preliminary Report

PURPOSE

This preliminary study evaluated the safety and effectiveness for off-label use of Neuroform EZ (NEZ) stents in the revascularization of hepatic artery stenosis (HAS) after orthotopic liver transplantation (OLT).

MATERIALS AND METHODS

Nine of 489 (5%) OLTs with HAS were managed with NEZ stents between September 2016 and July 2021. Stenting outcomes were evaluated based on the technical success rate, procedure-related complications, and primary patency.

RESULTS

A total of 10 NEZ stents (4.5 mm × 3 cm, n = 6; 4 mm × 3 cm, n = 4) were successfully deployed in 9 torturous hepatic arteries and in 1 relatively straight artery without any procedure-related complications. Combined thrombolysis (n = 3) and balloon angioplasty (n = 6) was performed. The median duration of follow-up was 438 days (range, 120-1126 days). Asymptomatic re-stenoses were detected in 2 stents on days 60 and 433 after stenting. A Kaplan-Meier curve predicted cumulative primary stent patencies at 1, 2, and 3 years of 90%, 75%, and 75%, respectively.

CONCLUSION

NEZ stents can be safely used to treat HAS after OLT with high technical success and favorable primary patency.

Analysis of Hepatic Arterial Reconstruction Technique Using Surgical Loupes for Living-Donor Liver Transplantation: Results From a Single Center

BACKGROUND

The reconstruction of the hepatic artery (HA) is the most complex step in living-donor liver transplantation (LDLT) owing to the artery's smaller diameter and the increased risk for HA-related complications. In this study, we presented our HA anastomosis technique for LDLT, which employed interrupted sutures using magnifying loupes.

MATERIALS AND METHODS

Since January 2019, we retrospectively analyzed 179 LDLTs that were performed at our center. HA anastomosis was performed under a loupes magnifier (2.5 or 4.5 × ) by the same surgeon.

RESULTS

There were 65 female and 114 male recipients with a mean age of 41.6 ± 21.6 years. Of the recipients, 34 were children. HA thrombosis (HAT) was seen in 3 recipients (1.67%; 1 child and 2 adults) in this series. HAT occurred on the third, sixth, and seventh days after LDLT. HAT was successfully treated with interventional radiologic technique. All recipients are still alive with a patent HA.

CONCLUSION

The use of magnifying surgical loupes and interrupted sutures to perform HA reconstruction is safe, feasible, and yields a low rate of HAT. Also, endovascular treatment can be used safely for treatment of HAT within the first week after LDLT with a high success rate and is not associated with major complications.

Management and outcome of hepatic artery thrombosis after pediatric liver transplantation

BACKGROUND

Pediatric LT are at particular risk of HAT, and its management still constitutes a matter of debate. Our purpose was to study predisposing factors and outcome of HAT post-LT, including the impact of surgical revisions on survival and biliary complications.

METHODS

Among 882 primary pediatric LT performed between 1993 and 2015, 36 HAT were encountered (4.1%, 35 fully documented). Each HAT case was retrospectively paired with a LT recipient without HAT, according to diagnosis, age at LT, type of graft, and era.

RESULTS

Five-year patient survivals were 77.0% versus 83.9% in HAT and non-HAT paired groups, respectively (P = .321). Corresponding graft survivals were 20.0% versus 80.5% (P < .001), and retransplantation rates 77.7% versus 10.7%, respectively (P < .001). One-year biliary complication-free survivals were 16.6% versus 83.8% in the HAT and non-HAT groups, respectively (P < .001). Regarding chronology of surgical re-exploration, only HAT cases that occurred within 14 days post-LT were re-operated, fourteen of them being explored within 7 days post-LT (revascularization rate: 6/14), versus two beyond 7 days (no revascularization). When revascularization was achieved, graft and biliary complication-free survival rates at 1 year were 33.3% and 22.2%, respectively, both rates being 0.0% in case of failure.

CONCLUSIONS

The pejorative prognosis associated with HAT in terms of graft survival is confirmed, whereas patient survival could be preserved through retransplantation. Results suggest that HAT should be re-operated if occurring within 7 days post-LT, but not beyond.

Time is of the essence: A single-center experience of hepatic arterial supply impairment management in pediatric liver transplant recipients

BACKGROUND

Impairment of hepatic arterial flow including hepatic arterial thrombosis (HAT), hepatic arterial stenosis (HAS), and splenic artery steal syndrome (SASS) is potentially life-threatening complications. The proposed early diagnosis and urgent treatment strategy of graft arterial flow reduction aim to decrease morbidity and mortality.

METHODS

Pediatric patients with known hepatic arterial flow impairment were retrospectively reviewed. Patients were grouped by occlusive (HAT) and non-occlusive (HAS/SASS) arterial flow reduction. Patients with HAT were further divided in two groups based on the estimated maximal hepatic artery occlusion time ≤8 and >8 hours.

RESULTS

Impairment of hepatic arterial flow developed in 32 of 416 pediatric liver transplant recipients. HAT, HAS, and SASS incidences were 4.1% (n = 17), 2.2% (n = 9), and 1.4% (n = 6), respectively. Neither graft loss nor death occurred in the non-occlusive group. The probabilities of sepsis (OR, 1.7; 95% CI, 1.14-2.53; P=.008) and graft loss or death (OR, 1.42; 95% CI, 1.04-1.92; P=.046) were higher in the occlusive group. Patients with estimated maximal duration of hepatic artery occlusion ≤ 8 hours (n = 7; 41.2%) did not have ischemic-type biliary lesions and sepsis (P=.044 and 0.010, respectively) but had excellent 3-year graft survival compared with > 8 hours group (100% vs 40%; P=.037). Multivariate analysis revealed HAT manifestation by fever was associated with increased chances of graft loss or death.

CONCLUSION

Occlusive arterial complications impose higher risks of graft loss and death. Thorough arterial supply monitoring by Doppler ultrasonography and urgent endovascular arterial flow restoration may salvage both graft and the recipient.

Treatment of Hepatic Artery Stenosis in Liver Transplant Patients Using Drug-Eluting versus Bare-Metal Stents

Hepatic artery stenosis after liver transplant is often treated with endovascular stent placement. Our institution has adopted use of drug-eluting stents, particularly in small-caliber arteries. We aimed to compare patency rates of drug-eluting stents vs. traditional bare-metal stents. This was a single-institution, retrospective study of liver transplant hepatic artery stenosis treated with stents. Primary patency was defined as time from stent placement to resistive index on Doppler ultrasonography (<0.5), hepatic artery thrombosis, or any intervention including surgery. Fifty-two patients were treated with stents (31 men; mean age, 57 years): 15, drug-eluting stents; 37, bare-metal stents. Mean arterial diameters were 4.1 mm and 5.1 mm, respectively. Technical success was 100% (52/52). At 6 months, 1, 2, and 3 years, primary patency for drug-eluting stents was 80%, 71%, 71%, and 71%; bare-metal stents: 76%, 65%, 53%, and 46% (p = 0.41). Primary patency for small-caliber arteries (3.5–4.5 mm) with drug-eluting stents was 93%, 75%, 75%, and 75%; bare-metal stents: 60%, 60%, 50%, and 38% (p = 0.19). Overall survival was 100%, 100%, 94%, and 91%. Graft survival was 100%, 98%, 96%, and 90%. Stenting for hepatic artery stenosis was safe and effective. While not statistically significant, patency improved with drug-eluting stents compared with bare-metal stents, especially in arteries < 4.5 mm in diameter. Drug-eluting stents can be considered for liver transplant hepatic artery stenosis, particularly in small-caliber arteries.

Safety and efficacy of an integrated endovascular treatment strategy for early hepatic artery occlusion after liver transplantation

BACKGROUND

Hepatic artery occlusion (HAO) after liver transplantation (LT) is typically comprised of hepatic artery thrombosis (HAT) and stenosis (HAS), both of which are severe complications that coexist and interdependent. This study aimed to evaluate an integrated endovascular treatment (EVT) strategy for the resolution of early HAO and identify the risk factors associated with early HAO as well as the procedural challenge encountered in the treatment strategy.

METHODS

Consecutive orthotopic LT recipients (n = 366) who underwent transplantation between June 2017 and December 2018 were retrospectively investigated. EVT was performed using an integrated strategy that involved thrombolytic therapy, shunt artery embolization plus vasodilator therapy, percutaneous transluminal angioplasty, and/or stent placement. Simple EVT was defined as the clinical resolution of HAO by one round of EVT with thrombolytic therapy and/or shunt artery embolization plus vasodilator therapy. Otherwise, it was defined as complex EVT.

RESULTS

Twenty-six patients (median age 52 years) underwent EVT for early HAO that occurred within 30 days post-LT. The median interval from LT to EVT was 7 (6-16) days. Revascularization time (OR = 1.027; 95% CI: 1.005-1.050; P = 0.018) and the need for conduit (OR = 3.558; 95% CI: 1.241-10.203, P = 0.018) were independent predictors for early HAO. HAT was diagnosed in eight patients, and four out of those presented with concomitant HAS. We achieved 100% technical success and recanalization by performing simple EVT in 19 patients (3 HAT+/HAS- and 16 HAT-/HAS+) and by performing complex EVT in seven patients (1 HAT+/HAS-, 4 HAT+/HAS+, and 2 HAT-/HAS+), without major complications. The primary assisted patency rates at 1, 6, and 12 months were all 100%. The cumulative overall survival rates at 1, 6, and 12 months were 88.5%, 88.5%, and 80.8%, respectively. Autologous transfusion < 600 mL (94.74% vs. 42.86%, P = 0.010) and interrupted suture for hepatic artery anastomosis (78.95% vs. 14.29%, P = 0.005) were more prevalent in simple EVT.

CONCLUSIONS

The integrated EVT strategy was a feasible approach providing effective resolution with excellent safety for early HAO after LT. Appropriate autologous transfusion and interrupted suture technique helped simplify EVT.

Endovascular Therapy of Arterial Complications Within the First Week After Liver Transplant

BACKGROUND

Recent radiologic advances have made endovascular treatment a very successful option for arterial complications after liver transplant. This article presents our experience of using endovascular treatments during the first week after liver transplant.

METHODS

This study is a retrospective, single-center analysis. Liver transplants performed between 2010 and 2018 were analyzed. All patients underwent Doppler ultrasonography on days 1 and 7. Endovascular therapy was indicated in hepatic artery thrombosis diagnosed early after transplant and in stenosis when hepatic narrowing was > 70%. Patients were treated with subcutaneous anticoagulant therapy and with antiplatelet agents after endovascular therapy.

RESULTS

Seven patients (1.1%) were included in the study. Stenosis was the reason in 5 patients while 2 patients had symptoms of thrombosis. The first 2 patients were initially treated with angioplasty; both had restenosis and were treated with angioplasty and stent placement, respectively. The 5 most recent patients received stenting as a primary treatment. Two of these patients developed a new stenosis. No patient developed any hepatic artery complication related to the procedure, and only 1 patient experienced a postprocedure complication (femoral artery pseudoaneurysm), which was managed conservatively. No patient required retransplant. After a median follow-up of 48 months (range, 35-85 months) 1 patient had died, and the rest were alive and asymptomatic.

CONCLUSIONS

Although there is scant experience of the use of endovascular therapy very shortly after liver transplant, recent advances in interventional radiology have made the technique feasible and safe, and it achieves a high success rate.

The devil is in the detail: current management of perioperative surgical complications after liver transplantation

PURPOSE OF REVIEW

Despite advances in the field, perioperative morbidity is common after liver transplantation. This review examines the current literature to provide up-to-date management of common surgical complications associated with liver transplantation.

RECENT FINDINGS

Research focuses on problems with anastomoses of the vena cava, portal vein, hepatic artery, and bile ducts. Interventional endoscopic and radiological techniques are used more frequently to avoid reoperation.

SUMMARY

Advances in the management of perioperative surgical complications have focused on minimally invasive measures that successfully treat technical problems with implantation of liver allografts from both living and deceased donors.

Hepatic artery stenosis angioplasty and implantation of Wingspan neurovascular stent: A case report and discussion of stenting in tortuous vessels

BACKGROUND

Hepatic artery stenosis is a complication of orthotopic liver transplant occurring in 3.1%-7.4% of patients that can result in graft failure and need for re-transplantation. Endovascular therapy with angioplasty and stenting has been used with a high degree of technical success and good clinical outcomes, but tortuous hepatic arteries present a unique challenge for intervention. Suitable stents for this application should be maneuverable and conformable while also exerting adequate radial force to maintain a patent lumen.

CASE SUMMARY

Herein we report our experience with a neurovascular Wingspan stent system in a challenging case of recurrent hepatic artery stenosis and discuss the literature of stenting in tortuous transplant hepatic arteries.

CONCLUSION

Wingspan neurovascular stent is self-expanding, has good conformability, and adequate radial resistance and as such it could be added to the armamentarium of interventionalists in the setting of a tortuous and stenotic transplant hepatic artery.

Percutaneous Transarterial Stent Placement in a Transplant Liver Hepatic Artery Complicated by Angioplasty Balloon Rupture and Fragmentation

The incidence of posttransplant hepatic arterial stenosis (HAS) has been reported in 5 to 10% of orthotopic liver transplants and, left untreated, can lead to hepatic arterial thrombosis. Most vascular complications develop less than 3 months after initial transplant, with thrombosis representing over half of all complications. There has been a trend toward minimally invasive, endovascular techniques for treating HAS with angioplasty and stenting. In one review of endovascular therapies for HAS, primary technical success was achieved in 95% of the interventions. Complication rates following endovascular repair of HAS have been reported to be between 0 and 23% in the literature. The main risk factors for complications include tortuosity of the hepatic artery and history of a second liver transplant. Other associated risk factors include female gender, age greater than 60 years, prior history of transarterial chemoembolization, and multiple arterial graft anastomoses. The case presented here is representative of a complication of balloon rupture and fragmentation in a patient undergoing hepatic arterial stent placement post-liver transplant.

Transplant Hepatic Artery Stenosis: Endovascular Treatment and Complications

Hepatic artery stenosis (HAS) is an infrequent complication of liver transplant; if left untreated, it can lead to hepatic artery thrombosis with high risk of biliary necrosis and graft loss. HAS is diagnosed with screening Doppler ultrasound, together with computed tomography angiography and magnetic resonance angiography. Endovascular treatment with angioplasty ± stent placement is safe and effective with infrequent major complications; however, when complications occur, they can devastate long-term graft survival. Herein, we present two cases of HAS treated with balloon angioplasty with resultant major complications requiring operative intervention.

Primary Stent Placement for Hepatic Artery Stenosis After Liver Transplantation: Improving Primary Patency and Reintervention Rates

Recent studies have reported high rates of reintervention after primary stenting for hepatic artery stenosis (HAS) due to the loss of primary patency. The aims of this study were to evaluate the outcomes of primary stenting after HAS in a large cohort with longterm follow-up. After institutional review board approval, all patients undergoing liver transplantation between 2003 and 2017 at a single institution were evaluated for occurrence of hepatic artery complications. HAS occurred in 37/454 (8%) of patients. HAS was defined as >50% stenosis on computed tomography or digital subtraction angiography. Hepatic arterial patency and graft survival were evaluated at annual intervals. Primary patency was defined as the time from revascularization to imaging evidence of new HAS or reaching a censored event (retransplantation, death, loss to follow-up, or end of study period). Primary stenting was attempted in 30 patients (17 female, 57%; median age, 51 years; range, 24-68 years). Surgical repair of HAS prior to stenting was attempted in 5/30 (17%) patients. Endovascular treatment was performed within 1 week of the primary anastomosis in 5/30 (17%) of patients. Technical success was accomplished in 97% (29/30) of patients. Primary patency was 90% at 1 year and remained unchanged throughout the remaining follow-up period (median, 41 months; interquartile range [IQR], 25-86 months). Reintervention was required in 3 patients to maintain stent patency. The median time period between primary stenting and retreatment was 5.9 months (IQR, 4.4-11.1 months). There were no major complications, and no patient developed hepatic arterial thrombosis or required listing for retransplantation or retransplantation during the follow-up period. In conclusion, primary stenting for HAS has excellent longterm primary patency and low reintervention rates.

Transplant artery thrombosis and outcomes

Post-transplantation allograft arterial thrombosis is a well-recognized complication associated with solid organ transplantation. Much of the literature is centered on liver and kidney transplantation, which will therefore serve as the principle basis for this review, with a brief discussion on pancreas transplantation and associated arterial complications. The number of solid organ transplants has been steadily increasing over the past decade in parallel with growing demand for organs and expansion of the transplantation criteria for both donors and recipients. This increase has been accompanied by a number of innovative medical advances and surgical techniques, as well as improved imaging that has allowed for thoughtful exploration of vascular anatomic variants and the possibilities for transplant with which they are associated. It has also been accompanied by a growing field of behavioral research, as potential recipients must weigh the risk of accepting certain organs based on perceived outcomes that may differ according to the quality of the underlying organ. Improvements in imaging technology have brought greater sensitivity to detecting arterial complications in post-operative surveillance examinations and have allowed for further development of tailored endovascular and surgical interventions for transplant-associated vascular complications. This review will focus on post-transplantation solid organ allograft artery thrombosis, including discussion of risk factors, diagnostic imaging, natural history, and therapeutic options.