The comparison between ultrasonography and 99mTc-DMSA renal scan in estimation of kidney size

Introduction: Renal length measurement is an important diagnostic clue in several urinary tract abnormalities. Although ultra sonography is the most frequent used modality for renal size estimation, renal diameter assessment by 99mTc-DMSA scintigraphy is of great value. By now, pointing to the renal size in the 99mTc-DMSA scintigraphy report has not been recommended by guidelines. If the validity of 99mTc-DMSA scan for renal size assessment would be established and reported in routine clinical practice, it might be more helpful for diagnostic purposes obviating further modality use in kidney diameter assessment. Methods:70 patients (25 males and 45 females) with the age range of 1 month to 78 years old (Mean ± SD = 18.1 ± 19.3) were included in the study. The longest axis diameter of each kidney was calculated by ultra sonography and planar 99mTc-DMSA scintigraphy. The difference in renal size estimation between US and different projections of 99mTc-DMSA scan was assessed using generalized linear model repeated measurement, pair wise comparison in Post Hoc and Bland-Altman analysis. Results:16 (22.9%) reports were interpreted as normal study, while 54 patients had abnormality at least in one kidney. No significant difference was noticed between the kidney diameters in US as compared to the all views of 99mTc-DMSA scan. Only in the estimation of left kidney size using 99mTc-DMSA scan, there was significant difference between anterior and posterior oblique views as well as between lateral and posterior oblique views. Mean value of the differences (estimated bias) doesn't differ significantly from 0 on the basis of 1-sample t-test. Conclusion: 99mTc-DMSA scintigraphy is an accurate method for renal length measurement with excellent agreement with ultra sonography. Kidney length can be easily measured as a routine processing procedure of a 99mTc-DMSA scan and not only used for more accurate interpretation of the images but also added to the final report as valuable incremental information.