MR Assessment In Normal And Congenital Malformation Fetal Kidneys: A Preliminary Study

Objective: To investigate the feasibility and utility of fast MR imaging and diffusion weighted imaging(DWI) in fetal kidney, establish MR diagnostic criteria of normal fetal kidney, and evaluate the clinical application value in the assessment of fetal normal renal growth condition and the diagnosis of congenital kidney malformations.Materials and Methods: Three hundred and eighty-three healthy pregnant women performed fetal MR in our hospital from December 2014 to December 2015 were enrolled in this study, including 135 normal kidney fetuses in normal kidney group(gestational age 18–39.3 weeks, mean(29.7±4.6) weeks; maternal age 20-43 years, mean(29.6±4.9) years) and 40 congenital abnormal kidney cases in malformation kidney group(gestational age 23-38 weeks, mean(30.6±4.5) weeks;maternal age 19-39 years, mean(28.6±5.0) years) according to inclusion criteria.All cases were confirmed by follow-up. MR imaging was performed using a superconducting 1.5-Tesla magnet system(Philips Achiena) with a phasedarray coil placed over the mother’s pelvis. Patients were examined in free breathing and no sedation was administered either to the mother or to the fetus. Then, the multiplanar study of kidney was acquired by using the following sequences, including SSh TSE,Balance FFE, gradient echo T1 WI and DWI with b value of 800. All MR were interpreted by two radiologists in consensus. The bilateral renal length(RL), width(RW), thickness(RT), renal parenchyma thickness(RPT), renal pelvis width(RPW),kidney volume(RV), signal intensity of DWI and ADC value were measured.Intraclass correlation coefficient(ICC) analysis was calculated for the assessment of consistency or reproducibility. A paired t test analysis was applicated to compare parameters between bilateral kidneys. Spearman correlation analysis and monadic linear regression analysis were used to evaluate the correlation between each parameter to GA and calculate the regression equation. Mc Nemar chi-square test was applied to evaluate the accuracy in diagnosing renal malformations with prenatal MR an ultrasonography. P ≤ 0.05 was considered to be statistically significant.Results: In the normal kidney group, all fetal kidney parameters measured byMR had good reproducibility between inter-observers, intra-observers and both examination methods of MR and ultrasound, and RL showed best reliability and RPW minimum. RL, RW, RT, RPT, RPW, RV, signal intensity of DWI and ADC values of normal kidneys were(30.9±5.2)mm,(19.2±3.5)mm,(17.0±3.5)mm,(7.0±1.4)mm,(3.4±0.7)mm,(5763±2808)mm3,(420±84), and(1.285±0.181)×10-3mm2/s,respectively. There were no statistical differences between above parameters of the normal bilateral kidneys(P>0.05). Among them, RL, RW, RT, RPT, RPW and RV had positive correlation to GA(r=0.946, 0.866, 0.863, 0.770, 0.444, 0.899, P< 0.001).There was negative correlation between ADC value and GA(r = 0.864, P < 0.001),and no correlation between signal intensity of DWI and GA(P = 0.108). The best fit were expressed by the regression equations: RL=1.081GA-1.248,RW=0.673GA-0.809, RT=0.657GA-2.517, RPT=0.231GA+0.101,RPW=0.071GA+1.284, RV=555GA-10735 and ADC(×10-3mm2/s)=2.326-0.035 GA,respectively. The determination coefficient of RL was best and that of RPW was minimum. In the malformation kidney group, there were six cases of multicystic dysplastic kidney, five cases of pelvic ectopic kidney, 11 cases of ureteropelvic junction obstruction, two cases of renal duplication, 11 cases of renal duplication,three cases of bilateral renal dysplasia and two cases of renal cyst confirmed by follow-up. A total of 40 fetuses with kidney malformation included 12 cases with bilateral kindney and 28 cases with unilateral kidney, three cases with oligohydramnios and two fetuses with lungs dysplasia. MR findings correctly confirmed 38 in 40 cases with diagnostic accuracy of 95%, and ultrasounds correctly confirmed 35 in 40 cases with diagnostic accuracy of 87.5%. However, there was no statistical differences between the two methods(?2 = 2.25, P =0.125).Conclusion: Fast MR imaging and DWI were feasible in fetal kidney, which could not only evaluate fetal growth and development of normal kidney, but also had important value for diagnosis of the congenital kidney malformations, especially accompanied by oligohydramnios or lung hypoplasia. MR was a beneficial complement for fetal ultrasound and the combination of both methods could provide more comprehensive and more reliable radiological information for prenatal diagnosis of fetal kidneys.