ABSTRACT
Objective To investigate MRI features of metanephric adenoma(MA). Methods The retrospective analysis was performed on 6 adult patients that were scanned by regular, DWI and dynamic-enhancement MRI two weeks before surgery and diagnosed with MA pathologically after surgery. MRI features of lesions were observed. The signal intensities of lesions and contralateral normal renal cortex and medulla were respectively measured in plain scan, cortex, parenchyma and delayed phase. The enhancement magnitudes were calculated and the ADC values of lesions were measured. The differences of the signal intensity and enhancement magnitude were assessed by paired-sample t test among renal cotex, medulla and lesions. Results All lesions in MA were single and solid masses. Four cases occurred in the right kidney and two cases in the left kidney. The maximum diameters of the lesions ranged from 21 to 79 mm and the mean value was(41 ± 20)mm. Five cases were round or oval, while one case was irregular. The signal intensity in five cases was slightly lower in T2WI than the renal parenchyma, while one case was slightly higher than the renal parenchyma. The hyperintentsity of DWI and hypointensity of ADC were seen in all cases. The mean ADC value was(0.759 ± 0.211) × 10-3mm2/s. Hemorrhage were seen in two cases. Necrosis was present in one case and the capsules were seen in two cases. No scar, fat and swollen lymph nodes was seen in all cases . There was no statistical significance of the signal intensity between lesions measure in the plain scan and normal renal parenchyma(P>0.05). After adminstrating contrast materials, all lesions shown persistently mild to moderate enhancement . The siganl intensities of lesions measured in three phases after enhancement were signifcantly lower than those of the renal cortex(P0.05). But the signal intensities of leisons in delayed phases were significantly lower than thoseof renal medulla(P<0.05). Except from the difference of enhanced magnitude in cortex phase between lesions and normal medulla, significant differences were present between leisons and normal renal parenchyma(P<0.05). Conclusion MRI manifestations of MA show certain distinction, including, dominantly solid lesions, relatively lower signal intensity of lesions than that of renal cortex, slowly persistent enhancement, high signal on DWI and low signal on ADC.