新生大鼠窒息后缺氧脑损伤模型的磁共振影像与病理对照研究

Study of conventional MRI combined with SWI on brain damage after asphyxia in neonatal rats and compared with pathological

目的探讨常规MRI联合磁敏感加权成像(susceptibility-weighted imaging,SWI)对单纯缺氧法建立新生大鼠窒息后缺氧脑损伤模型病理类型的研究,并从组织学探讨缺氧对皮层及海马的影响。材料与方法将新生7日龄SD(Sprague Dawley)大鼠随机分为窒息组与对照组,窒息组幼鼠置于封闭小室内进行氧浓度为1%的缺氧5 min-氧浓度为21%的复氧3 min循环,累计缺氧30 min;对照组置于相同小室内相同时间。缺氧过程、缺氧后、造模后(1、3、7 d)进行行为学观察,并在扫描后1、3、7 d进行T1WI、T2WI及SWI序列扫描。根据MRI异常信号部位进行苏木素-伊红染色,观察异常信号区病理损伤类型。采用Nissl染色观察幼鼠皮层、海马齿状核(dentate grrus,DG)区、CA1(corn ammonis 1)及CA3(corn ammonis 3)区神经元存活情况;采用免疫组化染色检测凋亡相关蛋白Caspase-3的表达。结果幼鼠在缺氧后1、3、7 d均出现癫痫发作。MRI及SWI显示脑损伤类型包括脑室扩大、脑软化灶形成、脑室及脑实质内出血及微血管扩张。Nissl染色显示皮层、海马DG区神经元在缺氧后1、3、7 d均较对照组减少(P<0.05),CA3区神经元在缺氧后7 d减少(P<0.05)。免疫组织化学染色显示,海马DG区Caspase-3表达在缺氧后1、3、7 d均较对照组增高(P<0.05),皮层表达在缺氧后3、7 d均较对照组增高(P<0.05);海马CA1区、CA3区表达在缺氧后7 d较对照组增高(P<0.05)。结论MRI及SWI提示急性间歇性缺氧早期即可存在脑损伤,缺氧脑损伤可导致癫痫发作。提示临床将MRI及SWI作为有窒息病史且怀疑脑损伤患儿的常规检查,并应尽早进行临床干预。

Objective:To investigate the pathological types of hypoxic brain injury in neonatal rats after asphyxia by conventional magnetic resonance imaging(MRI)and susceptibility-weighted imaging(SWI),and to explore the effects of hypoxia on the cortex and hippocampus.Materials and Methods:Neonatal 7-day-old rats were randomly divided into asphyxiation and control groups.Pups in the asphyxiation group were placed in a closed chamber for a hypoxia with the oxygen concentration with 1%(5 min)-reoxygenation with the oxygen concentration of 21%(3 min)cycle for a cumulative hypoxia time of 30 min;control rats were placed in the same chamber with air for the same time.Behavioral changes and changes in general conditions of baby rats during and after hypoxia were observed during asphyxia.Abnormal behavioral observations were made and recorded at 1 d,3 d and 7 d after hypoxia.T1WI,T2WI and SWI sequences were performed at 1 d,3 d and 7 d after modelling.Hematoxylin-Eosin staining was performed according to the site of abnormal MRI signal to observe the type of pathological injury in the abnormal signal area.Neuronal survival in the cortical,dentate grrus(DG),CA1(corn ammonis 1)and CA3(corn ammonis 3)regions of the hippocampus of young rats was observed by Nissl staining;the expression of apoptosis-related protein Caspase-3 was detected by immunohistochemical staining.Results:Seizures were observed in pups at 1 d,3 d and 7 d after hypoxia.MRI and SWI showed types of brain injury including enlarged ventricles,foci of cerebral softening,intraventricular and parenchymal hemorrhage and microvascular dilatation.Nissl staining showed a decrease in neurons in the cortical and hippocampal DG regions at 1 d,3 d and 7 d after hypoxia compared to the control group(P<0.05),and a decrease in neurons in the CA3 region at 7 d after hypoxia(P<0.05).Immunohistochemical staining showed that the expression of Caspase-3 in the DG region of the hippocampus was higher than that of the control group at 1 d,3 d and 7 d after hypoxia(P<0.05),and the expression in the cortex was higher than that of the control group at 3 d and 7 d after hypoxia(P<0.05);the expression in the CA1 and CA3 regions of the hippocampus was higher than that of the control group at 7 d after hypoxia(P<0.05).Conclusions:MRI and SWI show that brain damage can be present early in acute intermittent hypoxia and that hypoxic brain damage can lead to seizures.This suggests that MRI and SWI should be used as routine clinical investigations in children with a history of asphyxia and suspected brain injury,and that early clinical intervention should be undertaken.