Visual Pathway Microstructure Alteration In Patients With Pituitary Adenomas By Diffusion Spectrum Imaging And Morphometry Analysis

Objective:This study was to investigate the microstructural alterations of the visual pathway and their correlation with VFD severity and chiasmal lift in patients with pituitary adenoma by using diffusion spectral imaging(DSI)and morphological analysis.We aim to achieve quantitative assessment of visual impairment in adenoma patients and provide an accurate imaging basis for clinical diagnosis and visual prognosis.Materials and Methods:In this study,65 patients with pituitary adenomas(mean age: 45.3 ± 13.3 years;38males)and 33 healthy controls(HCs,mean age: 44.1 ± 15.9 years;22 males),whose gender and age were well matched with adenoma patients,were recruited.Magnetic resonance imaging data and neuro-ophthalmological examination were obtained from each participant.The local Institutional Ethnic Committee approval was obtained.Written informed consent was obtained from all participants in this study before enrollment.The DSI data were performed with DSI-Studio(http://dsi-studio.labsolver.org/)and reconstructed using generalized q-sampling imaging(GQI).A quantitative anisotropybased generalized deterministic tracking algorithm was used to construct all the optic tracts.The mean quantitative anisotropy(QA)and generalized fractional anisotropy(GFA)values for each fiber bundle were calculated as the DSI parameters for the integrity evaluation of the visual pathway.The T1-weighted structural images were processed and analyzed using the CAT12 toolbox(http://dbm.neuro.uni-jena.de/cat/)implemented in SPM12(http://www.fil.ion.ucl.ac.uk/spm/software/spm12/).CAT12 offers processing pipelines for both Voxel-and surface-based morphometry(VBM and SBM)analyses.To focus on the gray matter loss and cortex thinning in visual areas,three regions of interest(ROIs)in the visual cortex were selected for further comparison: V1,V2,and hMT+,using the automatic brain segmentation and the Brodmann atlas.Average gray matter volume and cortical thickness values were calculated in each ROI for each participant.SPSS 22.0 statistical software was used for statistical analysis,and to calculate the statistical significance in the demographic and disease characteristics between the two groups.To identify quantitative abnormalities of visual pathway and distant optic structures,two-tailed t-tests were performed for diffusion and structural features between patients and healthy controls.The diffusion features included mean QA and GFA values in optic nerve(ON),optic tract(OT)and optic radiation(OR),respectively.The structural features comprised of average gray matter volume and cortical thickness in V1,V2,and hMT+,respectively.For the relationship between imaging features(diffusion and structural)and disease characteristics,Pearson correlation analyses were performed for all imaging features and the MD value.All patients were divided into severe(n = 23)and mild(n = 42)VFD groups,using the mean deviation value of-8 d B as the threshold.One-way ANOVA and Bonferroni test were used to compare imaging features among two subset VFD patients and healthy controls.All p value < 0.05 was considered statistically significant after Bonferroni correction for multiple comparisons.Results:There were no significant differences in age or sex between patients and controls(both p values > 0.05).In all patients,the BP-height was negatively correlated with the MD(p < 0.05).It indicated that increased chiasmal lift distance was associated with more severe VFD impairment.Compared with controls,patients with pituitary adenomas showed significantly decreased mean QA and GFA values in ON and OT(p < 0.05),but not in OR(p > 0.05).It verified the existence of microstructural damage of ON and OT in adenoma patients.DSI parameters in a subset of severe VFD patients(MD <=-8 d B,n = 23)with pituitary adenomas were significantly lower than those in mild VFD patients(p < 0.05)and controls(p < 0.05)in ON,OT and OR(p < 0.05).Neither of the mean QA and GFA values in OR were significantly different between patients with mild VFD and controls(p > 0.05).Compared with controls,the mean QA value in mild VFD patients was significantly different in ON(p < 0.05),but not in OT or OR(p > 0.05).There were no any significant differences of the mean GFA value between mild patients and controls in ON,OT or OR(all p values > 0.05).We found that,with subtle visual field damage,posterior optic structures may not show significant abnormalities.The SBM analysis showed that only the cortical thickness of V1 and V2 was significantly decreased in patients compared with controls(p < 0.05).In the further analysis,the cortical thickness of V1 in the subset of severe VFD patients and mild VFD patients were both significantly decreased than controls(p < 0.05),as well as the cortical thickness of V2 was significantly decreased in the subset of severe VFD patients compared with controls(p < 0.05).However,there were no significant differences in gray matter volume in overall intergroup comparisons and in subgroup comparisons(all p values > 0.05),using the VBM analysis.There were significant correlations between these two disease characteristics(MD and BP-height)and mean QA values,as well as mean GFA values in ON,OT and OR(p <0.05).These results suggested that reduced white matter integrity of the visual pathway was associated with more severe overall VFD impairment and chiasmal lift.However,the mean values of gray matter volume and cortical thickness in V1,V2 and hMT+were not correlated with the disease characteristics in adenoma patients(all p values >0.05,after Bonferroni correction).Conclusion:This study verified the existence of microstructural damage of visual pathway in adenoma patients.DSI may provide quantitative information to detect visual pathway abnormalities and be a potential diagnostic tool for determining the degree of visual field defects in patients with pituitary adenomas.