Influences of Anatomorphological Features of the Portal Venous System on Postsplenectomy Hemodynamic Characteristics in Patients With Portal Hypertension: A Computational Model-Based Study.

Tianqi Wang,Zunqiang Zhou,Fuyou Liang

doi:10.3389/fphys.2021.661030

Abstract

Splenectomy, as an effective surgery for relieving complications caused by portal hypertension, is often accompanied by a significantly increased incidence of postoperative thrombosis in the portal venous system (PVS). While the underlying mechanisms remain insufficiently understood, the marked changes in hemodynamic conditions in the PVS following splenectomy have been suggested to be a potential contributing factor. The aim of this study was to investigate the influences of the anatomorphological features of the PVS on hemodynamic characteristics before and after splenectomy, with emphasis on identifying the specific anatomorphological features that make postoperative hemodynamic conditions more clot-promoting. For this purpose, idealized computational hemodynamics models of the PVS were constructed based on general anatomical structures and population-averaged geometrical parameters of the PVS. In the models, we incorporated various anatomorphological variations to represent inter-patient variability. The analyses of hemodynamic data were focused on the spatial distribution of wall shear stress (WSS) and the area ratio of wall regions exposed to low WSS (ALS). Obtained results showed that preoperative hemodynamic conditions were comparable among different models in terms of space-averaged WSS and ALS (all were small) irrespective of the considerable differences in spatial distribution of WSS, whereas, the inter-model differences in ALS were significantly augmented after splenectomy, with the value of ALS reaching up to over 30% in some models, while being smaller than 15% in some other models. Postoperative ALS was mainly determined by the anatomical structure of the PVS, followed by some morphogeometrical parameters, such as the diameter and curvature of the splenic vein, and the distance between the inferior mesenteric vein and splenoportal junction. Relatively, the angles between tributary veins and trunk veins only had mild influences on ALS. In addition, a marked increase in blood viscosity was predicted after splenectomy, especially in regions with low WSS, which may play an additive role to low WSS in initiating thrombosis. These findings suggest that the anatomical structure and some morphogeometrical features of the PVS are important determinants of hemodynamic conditions following splenectomy, which may provide useful clues to assessing the risk of postsplenectomy thrombosis based on medical imaging data.

Highlights

Splenectomy is a surgery whose indications generally include spleen rupture, hypersplenism, and symptomatic splenomegaly (Cooper and Williamson, 1984; Weledji, 2014)
It was observed that the preoperative wall shear stress (WSS) differed considerably in spatial distribution among the models, the values of space-averaged WSS (SA-WSS) and area ratio of low WSS (ALS) were comparable
While postoperative thrombosis is a frequent surgical sequela in patients treated with splenectomy (Ikeda et al, 2005; Ushitora et al, 2011) and numerous studies have been devoted to exploring its etiology and associated factors (Sobhonslidsuk and Reddy, 2002; Winslow et al, 2002; Ruiz-Tovar and Priego, 2016; Tsamalaidze et al, 2018), well-established schemes for patient-specific risk assessment remain absent in current clinical practice

Summary

Introduction

Splenectomy is a surgery whose indications generally include spleen rupture, hypersplenism, and symptomatic splenomegaly (Cooper and Williamson, 1984; Weledji, 2014). With regard to postsplenectomy thrombosis, the roles of blood constituents have been investigated extensively (Sobhonslidsuk and Reddy, 2002; Kinjo et al, 2010; Ruiz-Tovar and Priego, 2016) Major findings in this direction include: (1) thrombophilic disorders (e.g., deficiencies of protein C, protein S, and antithrombin III, myeloproliferative disorders, and antiphospholipid syndrome) were associated with PVST, and (2) low white cell count or high platelet count might increase the risk of postsplenectomy thrombosis. Controversies remain about whether these factors are able to sufficiently account for the clinically observed inter-patient differences in the risk of postsplenectomy thrombosis (Winslow et al, 2002; Tsamalaidze et al, 2018) In this context, some studies turned to investigating other factors that are related to hemodynamic conditions in the portal venous system (PVS). Relevant evidences have been reported by studies on thrombotic problems in other vessels or implantable artificial devices (Malek et al, 1999; Corbett et al, 2010; Gorring et al, 2015; Poredos and Jezovnik, 2018), among which, low wall shear stress (WSS), which can induce endothelial dysfunction and promote focal platelet aggregation and fibrin deposition, has been demonstrated to be a major driving factor for thrombosis

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