【作者】 于龙华；

【导师】 王健；

【作者基本信息】 第三军医大学 ， 影像医学与核医学， 2014， 博士

【摘要】 研究背景和目的青光眼是世界范围内不可逆性致盲的首要原因，以进行性的视网膜神经节细胞（retinal ganglion cells，RGCs）及其轴突丢失为主要特征。原发性开角型青光眼（primaryopen angle glaucoma, POAG）是青光眼的主要表现类型之一，其发病隐匿，潜在危险性更大。尽管RGCs渐进性丢失是其主要的病理特征，但越来越多的组织学及影像学研究证实可能整个视觉通路均受累及，包括RGCs、外侧膝状体（lateral geniculatenucleus, LGN）以及初级视皮质（primary visual cortex, V1）等。目前POAG被认为是由环境和遗传因素导致的复杂性性视通路病变，但具体的发病机制仍需进一步探讨。近年来采用磁共振成像（magnetic resonance imaging，MRI）技术对POAG视觉通路损害的研究引起了广泛关注。该技术可以从视觉皮质结构、视通路白质纤维束、任务态和静息态的脑功能等诸多角度揭示POAG视觉通路的改变情况。但既往的MRI研究多关注于POAG的中晚期，疾病早期的中枢视觉通路是否改变仍不明了，而且POAG患者皮质形态的改变进程以及POAG早期静息状态下功能的改变在疾病神经机制中起到的作用尚不清楚。因此，本项研究基于视皮质通路多参数的形态分析以及静息态功能磁共振（resting-state functional magnetic resonance imaging, R-fMRI）的方法，研究POAG患者特别是疾病早期中枢视区的皮质结构和相关脑区的神经元功能改变，探讨该病可能的发病机制并为临床治疗提供有效的依据。材料和方法1.采集36例双眼POAG患者和40例匹配的正常志愿者的3D T1加权高分辨率MRI数据，采用CIVIET软件（1.1.9版本，蒙特利尔神经病研究所，加拿大）进行全脑皮质厚度分析，检测POAG患者可能存在的皮质厚度改变并与视网膜神经纤维层（retinal nerve fiber layer, RNFL）厚度做相关分析。随后POAG患者组被分成轻重两个亚组，比较视区皮质厚度随疾病严重程度的改变情况。2.采集20例早期（轻度组）、17例中晚期（重度组）的双眼POAG患者和20例匹配的健康志愿者（对照组）的TI加权高分辨率MRI数据。基于感兴趣区（regionof interest, ROI）分析的方法V1、V2（纹前皮质）和V5/MT+（颞中回视区）的皮质厚度，数据处理由FreeSurfer软件（5.3.0版本，麻省总院，波士顿，美国）完成。比较三组间的皮质厚度差异，并分析各ROI双侧的皮质厚度与双侧的RNFL厚度和视野MD值的相关性。3.采用第二部分的MRI数据，按照视网膜映射（中心视角10°）把V1和V2分别细分为前后两个亚区，同样纳入V5/MT+区作为ROI。分析V1和V2前、后亚区以及V5/MT+区的多参数皮质结构改变。比较三组间形态学指标的差异，并分析皮质厚度与关键性临床指标之间的相关性。4.采集21例POAG早期患者和20例健康志愿者的R-fMRI和高分辨率T1结构像数据，计算全脑比率低频振荡波幅值（fALFF）得到活动改变脑区，并把fALFF改变区（左侧楔前叶）与双侧V1、V2、V5/MT+区一并纳入作为ROI，分析与全脑功能连接的强度改变。结果：1.全脑皮质厚度分析结果：POAG组在双侧的距状沟前份的视皮质厚度明显变薄（右侧的BA17，左侧的BA17和BA18）。另有较小的皮质厚度减低区呈现在左侧的颞中回（BA37）和梭状回（BA19）。相关分析：左侧和右侧的距状沟皮质厚度与RNFL厚度呈正相关（左侧r=0.44，P=0.01；右侧r=0.38；P=0.03）。重度亚组左侧和右侧的RNFL厚度以及皮质厚度与轻度亚组比较均显著变薄。 RNFL厚度左侧：59.2±18.1vs.77.3±13.0μm（P=0.001）；右侧：59.2±14.5vs.73.3±19.0μm（P=0.020）；皮质厚度左侧：2.46±0.18vs.2.59±0.10mm（P=0.014）；右侧：2.56±0.16vs.2.70±0.14mm（P=0.009）。2.基于ROI的皮质厚度分析结果：与正常组比较，重度组左侧的V1和双侧的V2以及V5/MT+区皮质厚度明显减低，轻度组双侧的V5/MT+区皮质厚度显著变薄；三组间的平均皮质厚度随疾病加重呈减低趋势，重度组双侧的V2区皮质厚度较正常组和轻度组均明显变薄。双侧的V2区（r=0.38，P=0.02）和V5/MT+区（r=0.44，P=0.006）的皮质厚度与双侧的RNFL厚度呈正相关。双侧所有ROI的皮质厚度均与双侧的视野MD值呈正相关（V1：r=0.34，P=0.04；V2：r=0.42，P=0.009；V5/MT+：r=0.37，P=0.03）。3.基于ROI的形态学分析结果：皮质厚度：与正常对照组比较，重度组的V1前亚区（P=0.010），V2前亚区（P=0.011）和V5/MT+（P=0.016）区皮质厚度显著减低，轻度组V5/MT+区皮质厚度明显变薄（P=0.025）。重度组的V2后亚区皮质厚度较轻度组（P=0.002）和正常对照组（P=0.000）均显著减低。重度组V2后亚区灰质体积较正常对照组（P=0.001）和轻度组（P=0.034）均显著性减少。重度组V5/MT+区的平均曲率较正常组（P=0.031）显著改变。但三组间表面积无显著差异（P>0.05）。皮质厚度相关分析：V5/MT+区与RNFL厚度正相关（r=0.42，P=0.01）。重度组V1前亚区与RNFL厚度有相关趋势（r=0.46，P=0.08）。4.全脑静息态fALFF与功能连接分析结果：与对照组比较，POAG早期患者的左侧楔前叶（BA7），左侧角回（BA39）fALFF值呈显著减低（P <0.05,AlphaSim校正）。功能连接结果显示患者组与左侧楔前叶（BA7）和双侧V5/MT+连接强度较对照组减低的区域主要包括：动眼区(BA8)、额回（BA9、BA10、BA11）、前扣带回（BA24）、左侧小脑后叶和小部分颞中回区域（BA39），这些脑区基本与背侧注意网络一致。与V1和V2区连接强度减低的区域包括左侧前扣带回和左侧小脑后叶。患者组未发现fALFF或功能连接强度较对照组增高的区域。结论：1.全脑皮质厚度分析发现皮质改变区域主要位于距状沟周围皮质（BA17和BA18区），并且与临床关键指标RNFL厚度呈正相关，说明皮质厚度分析结果准确可靠，可作为判断POAG患者疾病严重程度的影像学指标。POAG患者视觉皮质萎缩揭示视觉中枢参与了其中的发病机制，但是基于全脑的皮质厚度分析不能提供解剖或者功能具体分区内的整体特性，也无法进行个体化的诊断。2.基于ROI的皮质厚度分析发现POAG早期患者V5/MT+区存在皮质萎缩，并显示随疾病严重程度的增加视皮质厚度的呈进行性减低。结果提示POAG早期视皮质就已参与了其中的病生机制，为临床早期干预治疗和指定策略防止脑神经损伤提供了影像学证据。3.基于视网膜皮质映射的形态学结构分析能够提供更多的POAG患者视皮质改变信息，结果表明皮质厚度是POAG患者视皮质改变的敏感性和可靠性指标，且V1和V2细分亚区之后更能客观地评价视区内的改变。结果提示V5/MT+区可能是POAG早期视皮质结构改变的关键脑区。4. R-fMRI结果显示POAG早期患者的背侧注意网络受到了影响。楔前叶（BA7）和V5/MT+可能是POAG早期患者功能改变的关键脑区，其所处的背侧视觉通道在POAG早期的发病机制中起到了关键的作用。更多还原

【Abstract】 Background and purposeGlaucoma is the leading cause of irreversible blindness worldwide, characterized byprogressive loss of retinal ganglion cells (RGCs) and degeneration of their axons in opticnerve (ON).Primary open-angle glaucoma (POAG) is the most common type of glaucoma.Although RGCs death is the major pathological hallmark of POAG, findings from animalexperiments, human autopsy and glaucoma patient studies indicated that the whole visualpathway may be involved in glaucomatous damage, including the RGCs, the lateralgeniculate nucleus (LGN) and the primary visual cortex (V1). POAG is currentlyconsidered the complicated optic neuropathy caused by environmental and genetic factors,but the pathogenesis of POAG remains elusive.Recently, studies on the disruption of the visual pathway in POAG have been widelyconcerned by using magnetic resonance imaging (MRI) method. Based on the neuroimagingtechnology, the alternations of visual pathway in POAG can be revealed in both thestructure (i.e. grey matter and white matter) and function. However, the previous MRIstudies are mainly focused on the advanced or severe stages of POAG and the alterations ofcentral visual pathway in the early stage of disease are still unknown. In addition,glaucomatous damage of the visual cortex has seldom been studied by usingmulti-parameter shape analysis and resting-state functional magnetic resonance imaging(R-fMRI) method. Thus, the objective of this study was to investigate possiblymorphological and functional changes of central visual pathway in POAG by usingmulti-modal MRI.Material and methodThe present study was divided into four parts:1. Thirty-six patients with bilateral POAG patients and forty matched health controlswere enrolled in this study.3D high-resolution structural T1images were obtained by using a3-Tesla MR scanner with an8-channel phased-array head coil. Cortical thickness wasprocessed using the automated CIVET pipeline (version1.1.9; Montreal NeurologicalInstitute at McGill University, Montreal, Quebec, Canada) to assess the possible changesbetween the patients and controls, and the correlation between the retinal nerve fiber layer(RNFL) thickness and cortical thickness was also investigated. Finally, the patients weresplit into mild and severe sub-groups for investigation of the relationship between POAGstage and cortical changes.2. Twenty normal controls (NC),20mild (MP) and17severe (SP) POAG patientswere recruited and scanned using the3-Tesla MR scanner. Cortical thickness analyses withregions of interest (ROI) was performed using FreeSurfer (version5.3.0,http://surfer.nmr.mgh.harvard.edu) to assess the cortical changes (V1, V2and V5/MT+)among the three groups. Finally, the associations of cortical thickness with RNFL thicknessand mean deviation (MD) of visual field were analyzed.3. Twenty normal controls (NC),19mild (MP) and17severe (SP) POAG patientswere recruited and scanned using magnetic resonance imaging. Multi-parametricmorphologic analyses (cortical thickness, volume, surface area and mean curve) with ROIwere performed by using FreeSurfer pipeline to assess the cortical changes (V5/MT+,anterior and posterior subregions of V1and V2) among the three groups. The correlationsbetween cortical thickness and clinical measurements (RNFL thickness and MD of visualfield) were also analyzed.4. Twenty-one patients with bilateral early stage of POAG patients and20matchedhealth controls were enrolled in this study. R-fMRI data and3D high-resolution structuralT1images were obtained using the3-Tesla MR scanner. Fractional amplitude of lowfrequency fluctuation (fALFF) method were applied to investigate the functional changesbetween patients and health controls. Functional connectivity was calculated by using theseed voxel correlation approach (precuneus, V1, V2and V5/MT+areas).Results:1. Compared with the normal controls, POAG patients showed significantlydecreased bilateral cortical thickness in the calcarine sulci (right BA17, left BA17and BA18) and in some smaller other regions including the left middle temporal gyrus (BA37) andthe fusiform gyrus (BA19)(P <0.005, uncorrected). The left and right cortical thickness of the calcarine sulcus correlated positively with the RNFL thickness (left, r=0.44, P=0.01;right, r=0.38, P=0.03).The significant difference was also found in cortical thickness ofthe calcarine sulcus and RNFL thickness between the mild and severe sub-groups. RNFLthickness (mild versus severe group), left:77.3±13.0vs.59.2±18.1μm (P=0.001); right:73.3±19.0vs.59.2±14.5μm (P=0.020). Cortical thickness (mild vs. severe), left:2.59±0.10vs.2.46±0.18mm (P=0.014); right:2.70±0.14vs.2.56±0.16mm (P=0.009).2. Compared with the NC group, the SP group had significantly lower thickness in theleft V1area and bilateral V2and V5/MT+visual cortices, whereas the MP group onlyexhibited a significant reduction of cortical thickness in the V5/MT+area. Although thethickness of these visual cortices was reduced in the SP group relative to the MP group, onlythe differences in the bilateral V2regions were statistically significant. The mean RNFLthickness in the POAG patients was positively correlated with cortical thickness in the V2(r=0.38, P=0.02) and V5/MT+(r=0.44, P=0.006) regions. Additionally, the mean MDwas also related to cortical thickness in the V1(r=0.34, P=0.04), V2(r=0.42, P=0.009)and V5/MT+(r=0.37, P=0.03) areas.3. Compared with the NC group, the SP group had significantly lower thickness in theanterior subregions of V1, V2and the V5/MT+visual cortices. Unexpectedly, corticalthinning in the posterior subregion of V2was statistically significant in the SP groupcompared with NC and MP group. In addition, the gray matter volume in posteriorsubregion of V2and was significantly decreased in the SP group compared with the NC (P=0.001) and MP (P=0.034) groups. Mean curvature in V5/MT+areas was significantlyincreased in the SP group compared with the NC group (P=0.031). There were nodifferences in surface area in all of the investigated visual areas among the three groups.Cortical thickness of V5/MT+was positively correlated with the mean RNFL thickness (r=0.42, P=0.01). In SP group, cortical thickness of the anterior subregion of V1alsoexhibited a correlation trend with the RNFL thickness (r=0.46, P=0.08).4. Significant between-group difference in fALFF was observed in left precuneus(BA7) and left angular gyrus (BA39/40)(P <0.05, AlphaSim corrected). In contrast, noregions in healthy controls showed higher fALFF than in POAG patients (P>0.05).Compared to normal controls, the early stage of POAG patients showed significantlydecreased functional connectivity with ROI in multiple brain regions including frontal gyrus (BA9, BA10and BA11), frontal eye field (BA8), left anterior cingulate gyrus (BA24), rightmiddle temporal gyrus (BA39) and left cerebellum posterior lobe (P <0.05, AlphaSimcorrected).Conclusion1. Cortical thickness analysis revealed cortical thinning in the visual-related cortex inPOAG patients, and the cortical thickness was correlated positively with the RNFLthickness. The results indicate that cortical thickness may be a sensitive measure fordetection of cortical alterations of the visual system in POAG. However, the whole-braincortical thickness based on vertex-based analysis could not reveal the changes of anatomicalor functional regions.2. This study provides direct in vivo evidence of the progressive thinning in the visualcortex in patients with POAG. The most significant novel finding is that cortical thicknessof the bilateral V5/MT+areas decreases in the early stage of POAG. These cortical changesindicated progressive neurodegeneration and early disruption of the visual cortex in POAG.Finally, we showed that the thickness of visual cortex correlated well with RNFL thicknessand visual field defects in POAG patients, which suggested that the thickness of visualcortex is helpful in detecting POAG pathology and could serve as a novel indicator ofdisease severity.3. This is the first study that provides direct in vivo evidence of the morphologicalterations in the visual cortex in POAG. The results indicated early disruption of the visualcortex in POAG and the glaucomatous process may be complex and heterogeneous. Ourfindings suggested that the thickness of visual cortex is more sensitive than the othermorphologic parameters.4. The dorsal attentional network may be affected inpatients with early POAG. Theprecuneus and V5/MT+may be the key regions and the dorsal visual pathway plays acritical role in the pathogenesis of early POAG.更多还原