[Measurement of renal index on X-CT]

Morphological measurements of the kidney were made using X-CT images. Anteroposterior width of the kidney as well as the renal sinus on both right and left sides and the transverse width of the first lumbar vertebral body were measured from CT images. Changes according to age in anteroposterior width of the kidney and the transverse width of the lumbar vertebral body were investigated. As to the ratio of the anteroposterior width of the kidney (both right and left) to the transverse width of the lumbar vertebral body, and the ratio of the anteroposterior width of the kidney to the anteroposterior width of the renal sinus, the changes due to aging and the differences between male and female were studied. 1) In actual CT measurements, the average anteroposterior width of the right kidney was 47 mm, while that of the left kidney was 49 mm. The left kidney was slightly larger than the right kidney with statistical significance. In subjects up to 19 years of age, both the anteroposterior width of the kidney and the transverse width of the lumbar vertebral body showed correlation with age, while after the age of 20, there was no age-related correlation. 2) The average ratio of the anteroposterior width of the kidney to the transverse width of the lumbar vertebral body was 1.13 for the right kidney and 1.19 for the left kidney. The difference between those two items was statistically significant and the changes due to aging were slight. During the age between 4 and 64 years, they were constant and no significant change was noticed. No difference between male and female was found. From the age of 65 years, a decreasing tendency was noticed. 3) The ratios of anteroposterior width of the kidney to the anteroposterior width of renal sinus for both right and left kidneys in males and females were found to be inversely correlated with age. They were similar to the changes due to aging in renal functions of the cortex system. As seen on CT image, the ratio of the anteroposterior width of the kidney to the transverse width of the lumbar vertebral body, and the ratio of the anteroposterior width of the kidney to the anteroposterior width of the renal sinus could be the index of both the size of the kidney and the thickness of the renal parenchyma respectively.