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The meso-Rex bypass is a physiological and anatomical bypass procedure for relief of extrahepatic portal vein obstruction and restoration of mesenteric venous return to the liver. Most patients who are candidates for the bypass are children or young adults with portal hypertension and hypersplenism secondary to cavernous transformation of the portal vein. Most frequently, the bypass utilizes an autologous venous graft to connect the intrahepatic left portal vein to the infrapancreatic superior mesenteric vein (SMV) re-establishing first-pass portal perfusion. We describe the preoperative imaging of the 92 bypass candidates, the surgical anatomy as reflected in postoperative imaging, and the imaging of bypass complications at our institution. Preoperative imaging with US, CT and MR is directed to demonstrate patency and size of the left portal vein and SMV, to define the extent of cavernous transformation and splanchnic collaterals, and to assess for any associated abdominal vascular or solid organ abnormalities. Postoperative imaging is aimed at diagnosing meso-Rex bypass stenosis or occlusion and the interventional management of these complications.

Background Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in children. The gold standard for diagnosis is liver biopsy. MRI is a non-invasive imaging method to provide quantitative measurement of hepatic fat content. The methodology is particularly appealing for the pediatric population because of its rapidity and radiation-free imaging techniques. Objective To develop a multi-point Dixon MRI method with multi-interference models (multi-fat-peak modeling and bi-exponential T2* correction) for accurate hepatic fat fraction (FF) and T2* measurements in pediatric patients with NAFLD. Materials and methods A phantom study was first performed to validate the accuracy of the MRI fat fraction measurement by comparing it with the chemical fat composition of the ex-vivo pork liver-fat homogenate. The most accurate model determined from the phantom study was used for fat fraction and T2* measurements in 52 children and young adults referred from the pediatric hepatology clinic with suspected or identified NAFLD. Separate T2* values of water (T2* W ) and fat (T2* F ) components derived from the bi-exponential fitting were evaluated and plotted as a function of fat fraction. In ten patients undergoing liver biopsy, we compared histological analysis of liver fat fraction with MRI fat fraction. Results In the phantom study the 6-point Dixon with 5-fat-peak, bi-exponential T2* modeling demonstrated the best precision and accuracy in fat fraction measurements compared with other methods. This model was further calibrated with chemical fat fraction and applied in patients, where similar patterns were observed as in the phantom study that conventional 2-point and 3-point Dixon methods underestimated fat fraction compared to the calibrated 6-point 5-fat-peak bi-exponential model ( P  < 0.0001). With increasing fat fraction, T2* W (27.9 ± 3.5 ms) decreased, whereas T2* F (20.3 ± 5.5 ms) increased; and T2* W and T2* F became increasingly more similar when fat fraction was higher than 15–20%. Histological fat fraction measurements in ten patients were highly correlated with calibrated MRI fat fraction measurements (Pearson correlation coefficient r  = 0.90 with P  = 0.0004). Conclusion Liver MRI using multi-point Dixon with multi-fat-peak and bi-exponential T2* modeling provided accurate fat quantification in children and young adults with non-alcoholic fatty liver disease and may be used to screen at-risk or affected individuals and to monitor disease progress noninvasively.

Background Brown adipose tissue (BAT) is identified in mammals as an adaptive thermogenic organ for modulation of energy expenditure and heat generation. Human BAT may be primarily composed of brown-in-white (BRITE) adipocytes and stimulation of BRITE may serve as a potential target for obesity interventions. Current imaging studies of BAT detection and characterization have been mainly limited to PET/CT. MRI is an emerging application for BAT characterization in healthy children. Objective To exploit Dixon and diffusion-weighted MRI methods to characterize cervical-supraclavicular BAT/BRITE properties in normal-weight and obese children while accounting for pubertal status. Materials and methods Twenty-eight healthy children (9–15 years old) with a normal or obese body mass index participated. MRI exams were performed to characterize supraclavicular adipose tissues by measuring tissue fat percentage, T2*, tissue water mobility, and microvasculature properties. We used multivariate linear regression models to compare tissue properties between normal-weight and obese groups while accounting for pubertal status. Results MRI measurements of BAT/BRITE tissues in obese children showed higher fat percentage ( P  < 0.0001), higher T2* ( P  < 0.0001), and lower diffusion coefficient ( P  = 0.015) compared with normal-weight children. Pubertal status was a significant covariate for the T2* measurement, with higher T2* ( P  = 0.0087) in pubertal children compared to prepubertal children. Perfusion measurements varied by pubertal status. Compared to normal-weight children, obese prepubertal children had lower perfusion fraction ( P  = 0.003) and pseudo-perfusion coefficient ( P  = 0.048); however, obese pubertal children had higher perfusion fraction ( P  = 0.02) and pseudo-perfusion coefficient ( P  = 0.028). Conclusion This study utilized chemical-shift Dixon MRI and diffusion-weighted MRI methods to characterize supraclavicular BAT/BRITE tissue properties. The multi-parametric evaluation revealed evidence of morphological differences in brown adipose tissues between obese and normal-weight children.

Abstract BACKGROUND: Although Onyx is widely used to embolize vascular lesions in adults, the safety and efficacy of this liquid embolic agent for use in children are not well studied. OBJECTIVE: To report our experience using Onyx in pediatric patients for a variety of cranial and spinal vascular lesions and tumors to determine its procedural complication rates, types, and clinical consequences and to highlight the indications for and principles of Onyx embolization in pediatric patients. METHODS: All pediatric Onyx embolization cases performed consecutively by the neuroendovascular services at our 2 institutions over a 5-year period were collected retrospectively and analyzed. RESULTS: Over the study period, 105 Onyx embolization procedures were performed in 69 pediatric patients with a mean follow-up of 112 days. Fifty-two patients harbored “primary” vascular lesions (malformations, fistulas, etc), whereas 17 patients had tumors. Complications occurred in 25 of 105 procedures (23.8%) and included ischemic infarct (7), asymptomatic nontarget embolization (4), intracerebral hemorrhage (3), microcatheter-related vessel perforation (3), retained microcatheter (2), cerebral edema (2), dimethyl sulfoxide-induced pulmonary edema (2), facial ischemia (1), and contrast-induced bronchospasm (1). Neurological morbidity occurred transiently after 10 procedures (9.5%) and permanently after 2 procedures (1.9%). There were no procedure-related deaths. Statistical analysis revealed no predictors of complications among the multiple potential risk factors evaluated. CONCLUSION: Our experience suggests that Onyx can be used effectively for embolization of pediatric cranial and spinal vascular lesions and tumors with low permanent morbidity; however, attention must be paid to the technical nuances of and indications for its use to avoid potential complications.

3 Discussion Endovascular embolization of perimedullary sAVFs in the pediatric population have been reported utilizing different embolization agents including detachable balloons, coils, polyvinyl alcohol particles, cellulose acetate polymer, n-butyl-cyanoacrylate (NBCA). Ethylene vinyl alcohol copolymer dissolved in dimethyl sulfoxide (DMSO), as a cohesive Onyx liquid embolic system, has been widely used for mechanical occlusion of CNS vascular malformations after it was licensed by Food and Drug Administration in 2005. Since it polymerizes slowly due to its lower viscosity, rapid catheter withdrawal is not required with Onyx embolization; thus providing enough time for multiple and more controlled injections in comparison to other liquid embolic agents such as NBCA.