Relation of spontaneous passage of ureteral calculi to size

A statistical analysis of 520 ureteral calculi was undertaken to elucidate the correlation between sizes of calculi and the probability of spontaneous passage. The mean length and width of 286 calculi passed spontaneously were 6.3 +/- 2.5 (S.D.) and 4.0 +/- 1.5 mm., respectively; those of 219 calculi removed surgically were 11.7 +/- 5.0 and 7.1 +/- 2.8 mm., respectively, the difference between the two groups being statistically significant. The rate of spontaneous passage of stones within one year after diagnosis was analyzed in relation to sizes of stones which were grouped at successive 1-mm. intervals both in length and width, the over-all rate of spontaneous passage being 53 per cent. It was concluded that stones larger than 8 mm. in width on x-ray films should be removed surgically, while in those smaller than 8 mm. in width higher chances of spontaneous passage by expectant treatment would be anticipated.