Basic And Clinical Studies In Posterior Reversible Encephalopathy Syndrome

Part1Animal model of hypertensive encephalopathy:MRI, DWI and PWI dynamic observationsObjective:PRES is a clinicoradiological entity with headache, visual changes, confusion, alterations of consciousness and acute onset of seizures. MR imaging shows vasogenic edema in the cortex and subcortical white matter predominantly involved in bilateral parieto-occipital lobes, which is of great importance in the diagnosis of the entity. The mechanism of PRES is not yet determined. Hypertensive encephalopathy is one of the severe complications of hypertension, also is a common cause of PRES with more homogeneity. The aim of the study is to investigate the MRI, DWI and PWI dynamic changes of hypertensive encephalopathy with rabbit animal models to further disclose the mechanism is PRES.Materials and methods:20adult New Zealand white rabbits were randomly divided into control group (group A) and observation group (group B), each group10cases. A modified Gloidblatt2K1C were used in rabbits to establish chronic hypertension model as control and intramuscular injection of Metaraminol Bitartrate for acute hypertension model as study. Routine rabbit brain MRI scanning, diffusion-weighted imaging were performed on a GE Signa HD3.0T MRI scanner and apparent diffusion coefficients were calculated in selected region of interest (ROIs) on workstation postprocessing, comparing the variations of signal intensities and ADC values in anterior, middle and posterior brain regions. The values of rCBV, rCBF and MTT were calculated in selected region of interest (ROIs), comparing the variations in anterior, middle and posterior brain regions.Results:Patchy slightly hypo-intensities on T1WI and hyper-intensities on T2WI were observed in posterior brain regions in nine rabbits of group B, which resolved completely on MRI scanning after drug withdrawal for one week. The character of vasogenic edema was demonstrated by the combination of slight hyper-intensities or iso-intensities on DWI and increased ADC values, which were significant (P<0.05) on the day3,6and9. No positive finding in the control group was obtained. The changes of CBF were most marked in posterior brain regions. The rCBV, rCBF increased after injection of Metaraminol Bitartrate and reached the peak on the ninth day, which was earlier than those of MAP on sixth day, and then decreased to a basically normal level after drug withdrawal for one week. The change of MTT was not significant.Conclusions:1) Vasogenic edema in posterior brain regions is the characteristic presentation of hypertensive encephalopathy;2) DWI could provide distributions and dynamic changes of brain edema;3) During the onset of hypertensive encephalopathy, the level of rCBF first increased and then declined, the peak of which was later than those of MAP. Part2Association of radiologic characteristics with blood pressure, cause and prognosis in posterior reversible encephalopathy syndromeObjective:Posterior reversible encephalopathy syndrome (PRES), as a result of hypertensive crisis, in which acute hypertension plays a key role. The relationships between blood pressure, cause and brain edema in PRES have not been well determined, as well as the relationships between atypical radiologic findings and clinical outcome. The purpose of this study is to determine the association between the degree and extent of edema in PRES with blood pressure, cause and investigate the significance of atypical radiologic findings in PRES. Material and Methods:Seventy patients with typical clinical symptoms and characteristic MR imaging findings of PRES were included in this study. The clinical records including of blood pressure, cuase were collected in all patient. The extent or degree of brain edema was graded by2observers blinded to patients'clinical record, as well as the atypical findings determined based on other scanning protocols.Results:1) The extents and degree of brain edema between normotensive group, hypertensive group and severe hypertensive group had no statistically significant difference (P>0.05).No correlation was found between the degree of brain edema and the levels of SBP, DBP, MAP, as well as PP;2) There was no difference in the extents and degree of brain edema between eclampsia group, hypertension group and other group (P>0.05),except that basal ganglia was more frequently involved in eclampisia group than in hypertension and others groups (F=6.54, P=0.002);3) For topographic lesion pattern, dominant parieto-occipital pattern in36patients, holohemispheric watershed pattern in14, superior frontal sulcus pattern in10, central pattern in seven and partial or asymmetric expression in three patients were found, no correlation was found between lesions distribution patterns and clinical causes; cytotoxic edema was not only correlated with higher edema scores (P=0.036), but also with intracranial hemorrhages (P=0.032) and without correlation with blood pressure, and vice versa;4) All six cases presented with headache, dizziness and limbs weakness without seizures, visual disorder or focal neurologic signs or symptoms with hyperintensity on T2WI in brainstem with dominantly medulla oblongata and cerebellum affected. Marked improvement and completely resolution on radiologic follow-up after proper treatment implied a benign process for the entity.Conclusions:1) Hypertension, as the common cause of PRES, is not the decisive factor or prerequisite for the development of brain edema;2) Brian edema in various causes with the similar distribution and degree have different pathogenesis involved in them;3) Atypical findings were not uncommon in PRES, the occurrence of cytotoxic edma, hemorrhage imply poor outcome;4) Brainstem-type PRES as a radiologic pattern has its distinctive clinical symptoms different from typical PRES patients. Part3Association of radiologic characteristics with biochemical parameters in posterior reversible encephalopathy syndromeObjective:The theory of blood-brian barrier (BBB) disruption induced by endothelial injury is increasing recognized for a large amount of atypical findings reports of PRES. The correlations of serum lactate dehydrogenase, as the marker of endothelial dysfunction, with the type and degree of brain edema have not been reported. In conditions with endothelial damage due to inflammatory processes, reduction of colloid osmotic pressure (COP) may facilitate fluid extravasation and edema development. The aim of the study is to determine the association between the degree and type of edema in posterior reversible encephalopathy syndrome (PRES) with biochemical parameter, especially serum lactate dehydrogenase.Material and Methods:Forty-nine patients with typical clinical symptoms and characteristic MR imaging findings of PRES were included in this study. The extent or distribution of brain edema was graded by2observers blinded to patients'clinical record, as well as the type of brain edema determined on FLAIR, DWI and ADC map. The levels of biochemical parameters were correlated with the degree and type of edema.Results:1) Among all of the49patients,19cases (38.8%) were eclampsic or pre-eclampsic patients, and18cases (36.7%) were chronic renal failure (CRF) patients, and12patients (24.5%) had different clinical conditons, no significant difference of edema scores was found between patients with eclampsia, CRF and other clinical conditions (P>0.05);2) Decreased serum albumin level (<35mg/mL) was noted in40/49patients (81.6%; mean±SD,23.6±5.8mg/dL) in general. Serum albumin level was not correlated with the scores of brain edema distribution (P>0.05);3) Increased serum LDH level (>226mg/dL) was noted in43/49patients (87.8%), serum LDH level were moderately correlated with the scores of brain edema distribution (Spearman's ρ-ttst, r=0.497, P=0.00). After linear regression, the influence of increased serum LDH level on the scores of brain edema distribution remained statistically significant (standardized coefficients=0.536, t=4.35, P=0.00. Conclusions:Increased serum LDH level, which plays an essential role in endothelial injury, may be a potential risk factor for the development of edema in PRES. Serum albumin may be one of the potential contributors to the development of edema in PRES, but not a decisive factor for edema type.