Pre- and postoperative imaging of the Rex shunt in children: what radiologists should know

A systematic review and meta-analysis of portal vein morphometry in pediatric and adult populations: Drawing the line between normal and abnormal findings

PURPOSE

The morphometry of the hepatic portal vein is of clinical importance, particularly in pre-operative assessments, surgical management, and diagnoses of liver conditions. This systematic review and meta-analysis aimed to characterize the morphometry of the normal portal vein in both pediatric and adult patients.

METHODS

The study, conducted using the PRISMA guidelines and registered with PROSPERO, utilized the MEDLINE, EMBASE, SCOPUS and Web of Science databases up to May 2020, and updated to May 2023. All studies reporting extractable data on diameter, length, and cross-sectional area (CSA) of the main, left, and right portal veins (PV, LPV, RPV, respectively) were included. The AQUA Tool was used to assess the quality of the included studies. Data analysis included subgroup analyses based on geographical location, sex, age, and imaging modality.

RESULTS

A total of 122 studies with 11,637 subjects were eligible for inclusion. Overall, the pooled mean diameter of the PV (PVD) was 10.09 mm (95% CI: 9.56-10.62). Significant differences in diameter were found between pediatric (6.60 mm; 95% CI: 5.38-7.82) and adult (10.72 mm; 95% CI: 10.25-11.19) subjects. Additionally, there was a significantly larger PVD measurement from computed tomography (CT) than other imaging modalities: CT, 13.28 mm (95% CI: 11.71-14.84); magnetic resonance imaging (MRI), 10.50 mm (95% CI: 9.35-11.66) and ultrasound (US), 9.81 mm (95% CI: 9.47-10.16). The mean diameters of the LPV and RPV were 8.27 mm (95% CI: 6.78-9.77) and 8.33 mm (95% CI: 6.70-9.95), respectively. Mean PV length in adults is 48.63 mm (95% CI: 35.63-61.64). Mean CSA of the PV was 1.09 cm2.

CONCLUSIONS

The study obtained aim to improve the understanding of portal vein anatomy, especially with relevance to surgical interventions of the liver in both pediatric and adult patients. Measurements from ultrasound imaging closely approximates the generated pooled PVD mean for pediatric and adult patients. CT imaging, however, significantly exceeded the established 13 mm threshold for adults. For pediatric patients, a threshold of 8 mm is proposed as a diagnostic upper limit for a normal PVD. Although not significant, the PVD decreased from the portal confluence towards its bifurcation.

Location and extent of cavernous transformation of the portal vein dictates different visceral side revascularization in Meso-Rex bypass

BACKGROUND

As an emerging standard of care for portal vein cavernous transformation (PVCT), Meso-Rex bypass (MRB) has been complicated and variated. The study aim was to propose a new classification of PVCT to guide MRB operations.

METHODS

Demographic data, the extent of extrahepatic PVCT, surgical methods for visceral side revascularization, intraoperative blood loss, operating time, changes in visceral venous pressure before and after MRB, postoperative complications and the condition of bypass vessels after MRB were extracted retrospectively from the medical records of 19 patients.

RESULTS

The median age of the patients (13 males and 6 females) was 32.5 years, while two patients were underage. Causes of PVCT can be summarized as follows: thrombophilia such as dysfunction of antithrombin III or proteins C; secondary to abdominal surgeries; secondary to abdominal infection or traumatic intestinal obstruction, and unknown causes. Intraoperatively, the median operation time was 9.5 h (7-13 h), and the intraoperative blood loss was 300 mL (100-1,600 mL). Ten cases used autologous blood vessels while 10 used allogeneic blood vessels. The vascular anastomosis was divided into the following types according to the site and approach: Type (T) 1-PV pedicel type, T2-confluence type, T3-major visceral vascular type; and T4-collateral visceral vascular type. Furthermore, the visceral venous pressure before and after MRB dropped significantly from 36 cmH2O (28-44) to 24.5 cmH2O (15-31) (P < 0.01). Postoperatively, one patient had delayed wound healing, two developed biochemical pancreatic fistulae, one experienced lymphatic leakage, the former caused by heat damage of the pancreatic tissues, the latter by cutting lymphatic vessels in the mesentery or removing the local lymph nodes during the process of separating the superior mesenteric vein, and one was re-operated on for an intervening intestinal fistulae. Postoperative enhanced CT scans revealed a significant improvement in abdominal varix in the patients with patent bypass, and at the 1-year postoperative follow-up, enhanced CT scans of six patients showed that the long axis of the spleen was reduced by ≥ 2 cm.

CONCLUSIONS

MRB can effectively reduce visceral venous pressure in patients with PVCT. It is feasible to determine the PVCT type according to the extent of involvement and to choose individualized visceral side revascularization performances.

Angiographic diagnosis for accurate assessment of congenital porto-systemic shunt and extrahepatic portal vein obstruction in children

BACKGROUND

Congenital porto-systemic shunt (CPSS) is a rare disease and can cause fatal complications. Accurate angiographic assessment is mandatory for proper treatment. Although technically difficult, we developed assessment techniques and assessed their accuracy. One technique came from evaluating patients with extrahepatic portal vein obstruction (EHPVO).

METHODS

We conducted a single center retrospective study to evaluate the efficacy of angiographic diagnostic procedure for the assessment of CPSS and EHPVO, and its impact on patients' subsequent interventions and clinical course. Eight patients with CPSS and two patients with EHPVO who underwent diagnostic angiography were included. Assessment of the intrahepatic portal vein was performed in all patients. The route of the shunt, and portal vein pressure under shunt occlusion, were also evaluated for patients with CPSS. Evaluation was first attempted with a balloon angiographic catheter (standard method). Three additional techniques were performed as needed: (i) direct wedge-catheter injection without balloon inflation, (ii) use of occlusion balloon in two patients, and (iii) hybrid angiography with sheath placement directly into the superior mesenteric vein.

RESULTS

The standard method was sufficient in four patients. On the other hand, all three techniques were required in two patients each. One lost contact during follow up, but all other patients underwent optimal intervention. There were no complications related to the angiographic procedure.

CONCLUSIONS

Use of direct wedge-catheter injection without balloon inflation, occlusion balloon, and hybrid catheterization improved the diagnostic yield in patients with CPSS or EHPVO.

Technical Aspects and Considerations of Meso-Rex Bypass Following Liver Transplantation With Left Lateral Segment Grafts: Case Report and Review of the Literature

In pediatric patients with extrahepatic portal vein obstruction and complications of portal hypertension, but with normal liver function, a meso-Rex bypass (MRB) connecting the superior mesenteric vein to the intrahepatic left portal is the favored surgical management. Pediatric patients with a history of a partial liver transplant (LT), especially living donors, are at greater risk for portal vein complications. Hence, an adequate knowledge of this technique and its additional challenges in the post-LT patient setting is crucial. We provide an overview of the available literature on technical aspects for an MRB post-LT. Preoperative considerations are highlighted, along with intraoperative considerations and postoperative management. Special attention is given to the even-more-demanding aspect of performing an MRB post-liver transplantation with a left lateral segment. Surgical alternatives are also discussed. In addition, we report here a unique case in which this surgical technique was performed on a complex pediatric patient with a history of a living-donor LT with a left lateral segment graft over a decade ago.

Value of preoperative computed tomography for meso-Rex bypass in children with extrahepatic portal vein obstruction

Background

Extrahepatic portal vein obstruction (EHPVO) is the most important cause of hematemesis in children. Intrahepatic left portal vein and superior mesenteric vein anastomosis, also known as meso-Rex bypass (MRB), is becoming the gold standard treatment for EHPVO. We analyzed the value of preoperative computed tomography (CT) in determining whether MRB is feasible in children with EHPVO.

Results

We retrieved data on 76 children with EHPVO (50 male, 26 female; median age, 5.9 years) who underwent MRB (n = 68) or the Warren procedure (n = 8) from 2013 to 2019 and retrospectively analyzed their clinical and CT characteristics. The Rex recess was categorized into four subtypes (types 1–4) depending on its diameter in CT images. Of all 76 children, 7.9% had a history of umbilical catheterization and 1.3% had leukemia. Sixteen patients (20 lesions) had associated malformations. A total of 72.4% of Rex recesses could be measured by CT, and their mean diameter was 3.5 ± 1.8 mm (range 0.6–10.5 mm). A type 1, 2, 3, and 4 Rex recess was present in 9.2%, 53.9%, 11.8%, and 25.0% of patients, respectively. MRB could be performed in patients with types 1, 2, and 3, but those with type 4 required further evaluation. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of CT were 100%, 83.8%, 42.1%, 100%, and 85.5%, respectively.

Conclusions

Among the four types of Rex recesses on CT angiography, types 1–3 allow for the performance of MRB.

Sonographic Evaluation of a Unique Meso-Rex Shunt: A Case Study

Portal hypertension is a result of an increase in intrahepatic resistance in the main portal vein. The Meso-Rex shunt is used to bypass the obstructed portal vein and restore the venous flow into the liver. This procedure alleviates the need for a hepatic transplant. The Meso-Rex shunt has proven to be an effective treatment for extrahepatic portal vein obstruction, thus saving children from a complete transplant. There are variants to this bypass surgery, and sonography is commonly used to assess the condition pre- and postoperatively. In this case, the shunt was uniquely different from the typical Meso-Rex bypass surgery. Particular vasculature made it imperative for the sonographer to review the prior sonograms and review the chart information before preforming the examination. It should also be noted that sonographers must adapt the protocols to give the utmost treatment.

Abdominal Applications of Pediatric Body MR Angiography: Tailored Optimization for Successful Outcome

OBJECTIVE. The purpose of this article is to summarize current common techniques and indications for pediatric abdominopelvic MR angiography and strategies for optimizing them to achieve successful outcomes. We also discuss newer MR angiography techniques, including whole-body imaging and blood pool contrast agents, as well as various approaches to reducing the need for anesthesia in pediatric MRI. CONCLUSION. Pediatric body vascular imaging presents a unique set of challenges that require a tailored approach. Emerging pediatric abdominopelvic MR angiography techniques hold promise for continued improvement in pediatric body MR angiography.

Vascular Anomalies of the Pediatric Liver

The liver is a unique organ as it receives afferent blood supply from the umbilical vein, portal vein, and hepatic artery in the developing embryo but has only one efferent drainage method, through the hepatic veins. In the postnatal period, about 70% of the afferent blood flow into the liver is from the portal venous system, unique vessels that begin and end in a capillary system. Vascular anomalies of the hepatic artery, hepatic veins, portal vein, and/or umbilical vein can be congenital or acquired secondary to inflammation and/or infection, trauma, systemic disorders, or iatrogenic causes. The vascular anomalies can be incidental findings at imaging, or the infant or child can present with symptoms such as abdominal pain and ascites, be diagnosed with gastrointestinal bleeding, and have abnormal liver function test results. Imaging can demonstrate vascular findings such as shunts, thrombosis, or collaterals; secondary parenchymal findings such as diffuse or focal abnormal enhancement patterns; and parenchymal lesions such as regenerative nodules. This article discusses and illustrates vascular disorders of the liver that may be encountered in the pediatric population. These include (a) normal vascular variants; (b) congenital anomalies (preduodenal portal vein and infradiaphragmatic total anomalous pulmonary venous return); (c) acquired thromboses (extrahepatic portal venous thrombosis); (d) inflammatory vascular conditions, which can result in hepatic artery aneurysms or pseudoaneurysms; (e) hepatic venous outflow disorders (veno-occlusive disease); and shunt lesions. Liver transplantation and associated vascular complications are a large topic and will not be reviewed in this article. Knowledge of the vascular and parenchymal changes seen with these entities can aid imaging diagnosis and guide appropriate management. ^©RSNA, 2019.

Evaluation of Rex Shunts

The purpose of the Rex shunt is to restore normal blood flow to a hemodynamically compromised liver that is otherwise normal. It has proven to be an effective treatment for children with extrahepatic portal vein thrombosis as in the case presented. The shunt allows blood from the superior mesenteric vein to bypass the obstructed extrahepatic portal vein and enter the liver through the still patent left portal vein. The operation is successful in more than 90% of patients. The name “Rex shunt” is derived from the location in the liver in which the shunt is placed, the area between segments three and four of the left lobe of the liver.