Evaluation of Acute Brain-Fat Embolism with Magnetic Resonace Imaging and Positron Emission Tomograpy in an Experimental Rat Model

骨折后可发生脂肪栓塞综合征。神经系统表现被认为是大脑多处病变的结果。在这种综合征的早期阶段，脑磁共振（MR）成像显示水肿的迹象。在实验研究中，油注射技术常被用来观察脑内的病理变化。然而，我们不认为这种技术完全模拟临床条件。在这项研究中，我们设计了一种技术，以更接近地模拟实际的临床状态，并揭示MR图像和组织学结果之间的关系。（方法）采用8周龄雄性大鼠。用戊巴比妥麻醉大鼠，在手术过程中一根股骨骨折。FES组大鼠经股骨髓腔静脉注射肝素化血液0.15ml/100 g。血液样本中没有骨髓碎片。注射肝素化生理盐水的大鼠 ...更多信息 0.15ml/100 g作为对照组。A）为了检查模型的特征，我们首先测量了FES组和对照组的平均血压、动脉血气、血红蛋白水平和血小板计数以及甘油三酯、脂肪酶和游离脂肪酸的浓度。然后，在注射后24小时和一周，我们使用自旋回波技术检查脑MR图像，1.5特斯拉（重复时间= 350-2000毫秒;回波时间= 25.80毫秒）。最后，我们用脂肪和磷钨酸苏木精染色法对脑、肺、脾和肾进行染色，以显示FES组的纤维蛋白栓子。B）将异常脑MR图像与脑组织学进行对照。C）注射后24小时，观察两组大鼠的活动，并在激进的八臂迷宫中测试其学习和记忆。（结果）FES组甘油三酯、脂酶、血小板、血红蛋白、PaCO_2均较对照组明显降低; FES组20只大鼠中有5只在24小时观察到T2加权图像上的高信号强度，显示脑水肿。然而，一周后就消失了。油红O和苏丹红III染色在肺和脾中发现了脂肪滴，但相同的染色未能显示脑中的脂肪滴。我们用锇染色法在脑和肺的毛细血管里发现了脂肪滴。在检查的器官中未发现沉积物。B）T2加权像上在同侧大脑皮质可见高信号病灶。然而，在组织学上，大脑皮层深部和双侧黑质的毛细血管中有大量的微脂肪栓塞。C：FES组和对照组之间没有差异。（结论）脂肪栓塞综合征急性期脑MR图像与脑组织学改变可能存在差异。少

(Background) Fat embolism syndrome may occur after bone fracture. The neurological manifestations are thought to be the consequence of multiple lesions of the brain. Brain magnetic resonance (MR) imaging in the early stage of this syndrome shows signs of edema. The oil injection technique is commonly used to investigate the pathological changes in the brain in the experimental studies. However, we do not believe that this technique fully simulate clinical conditions. In this study, we designed a technique to more closely simulate the actual clinical state and reveal the relation between the MR images and the histologic findings. (Methods) We used eight-weeek old male rats. The rats were anesthetized with pentobarbital, and one femoral bone was fractured during a surgical procedure. We intravenously injected 0.15 ml/100g of heparinized blood taken from femoral bone marrow cavity into rats (FES group). There was no bone marrow debris in blood sample. Rats injected with heparinized saline … More , 0.15 ml/100g, were used as controls (control group). A) To examine characteristics of the model, we first measured the mean blood pressure, arterial blood gases, hemoglobin level and platelet count and the concentrations of triglyceride, lipase and free fatty acid in the FES and control groups. Then, we examined the brain MR images using the spin-echo technique, 1.5 tesla (repetition times = 350-2000 msec ; echo times = 25,80 msec) at 24 hours and one week after the injection. Finally, we stained brains, lungs, spleens and kidneys with fat and phoshotungstic acid hematoxylin stain to reveal fibrin emboli in the FES group. B) We compared the abnormal brain MR images with the histology of the brain. C) We observed the activity of both groups of rats and tested their learning and memory in a radical eight-arm maze at 24 hours after the injection. (Results) A) A decrease in the levels of trigyceride, lipase, platelet, hemoglobin and PaCO_2 was noted in the FES group. In 5 of 20 rats in the FES group, high signal intensity on T2-welghted images, which showed edema in the brains, were observed at 24 hours. However, this disappeared one week later. Fat droplets were found in the lungs and spleens with oil red O and Sudan III stains, but the same stains failed to show fat droplets in brains. We found fat droplets in the capillaries of the brains and lungs with osmium staining. Fibrin deposits were not found in the organs examined. B) A high signal intensity lesion on T2-weighted was seen in the ipsilateral cerebral cortex. Histologically, however, there were massive micro-fat emboli in the capillaries of the deep cerebral cortex and substantia nigra bilaterally in the brain. C : No difference between FES and control groups was noted. (Conclusion) There is a possible discrepancy between brain MR images and the histologic changes of the brain in the acute stage of fat embolism syndrome. Less