Size matters: The width and location of a ureteral stone accurately predict the chance of spontaneous passage

Abstract

Objectives: To determine how to most accurately predict the chance of spontaneous passage of a ureteral stone using information in the diagnostic non-enhanced computed tomography (NECT) and to create predictive models with smaller stone size intervals than previously possible.

Methods: Retrospectively 392 consecutive patients with ureteric stone on NECT were included. Three radiologists independently measured the stone size. Stone location, side, hydronephrosis, CRP, medical expulsion therapy (MET) and all follow-up radiology until stone expulsion or 26 weeks were recorded. Logistic regressions were performed with spontaneous stone passage in 4 weeks and 20 weeks as the dependent variable.

Results: The spontaneous passage rate in 20 weeks was 312 out of 392 stones, 98% in 0-2 mm, 98% in 3 mm, 81% in 4 mm, 65% in 5 mm, 33% in 6 mm and 9% in ≥6.5 mm wide stones. The stone size and location predicted spontaneous ureteric stone passage. The side and the grade of hydronephrosis only predicted stone passage in specific subgroups.

Conclusion: Spontaneous passage of a ureteral stone can be predicted with high accuracy with the information available in the NECT. We present a prediction method based on stone size and location.

Key points: • Non-enhanced computed tomography can predict the outcome of ureteral stones. • Stone size and location are the most important predictors of spontaneous passage. • Prediction models based on stone width or length and stone location are introduced. • The observed passage rates for stone size in mm-intervals are reported. • Clinicians can make better decisions about treatment.

Keywords: Kidney stone; Renal colic; Spiral computed tomography; Ureter; Ureteral calculi.

Fig. 1

Flowchart showing exclusion criteria and numbers

Fig. 2

Distal ureteral stone: (a) axial, (b) coronal, (c) sagittal. Non-enhanced computed tomography of the urinary tract, window settings L300/W1120, showing a distal ureteral stone in a 39-year-old male. In each of the three reformats the largest diameter is measured. Stone length = the largest of these measurements (max[ax, cor, sag]). Stone width = the smallest of these measurements (min[ax, cor, sag]). Here the stone length = 7.2 mm and stone width = 4.6 mm

Fig. 3

Probability for spontaneous stone passage as a function of stone width, bone window (L300/W1120). (a) Upper ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the prediction short term: 0.92, long term: 0.93. (b) Lower ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.80, long term prediction: 0.83

Fig. 4

Probability for spontaneous stone passage as a function of stone width, soft tissue window (L50/W400). (a) Upper ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.92 long term prediction: 0.93. (b) Lower ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.81, long term prediction: 0.82

Fig. 5

Probability for spontaneous stone passage as a function of stone length, bone window (L300/W1120). (a) Upper ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.89, long term prediction: 0.89. (b) Lower ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.79, long term prediction: 0.83

Fig. 6

Probability for spontaneous stone passage as a function of stone length, soft tissue window (L50/W400). (a) Upper ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.90, long term prediction: 0.91. (b) Lower ureteral stones (univariate logistic regression curves). Error bars showing observed long-term 95% confidence intervals. AUC for the short term prediction: 0.80, long term prediction: 0.82