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Predicting Female Ureteral Length: A Mathematical Model

Bozzini G, Casellato S, Viganò A, Picozzi S and Carmignani

Aim: Ureteral double J stent placement is a common urological procedure. There are many conditions that lead to a stent placement and some of them, mainly in pregnant female patients, have the contraindications of using X-ray. This study has the aim of proposing a mathematical model able to predict ureteral length finding a correlation between different physical data. Materials and methods: Between June 2007 and July 2009, 100 female patients who underwent ureteral stent placement were enrolled in this study. Patients with septic conditions, history or evidence of TCC, congenital and acquired kidney or ureteral malformations, and previous ureteral surgery were not enrolled. Physical data for each patient were obtained (age mean 55.8 yrs range 18-89 SD 15.27, height mean 173 cm. range 160-182 SD 6.31, weight mean 75.33 kg range 62-94 SD 8.81). During the procedure, a previous ureteral retrograde pyelography was performed to individualize the pyeloureteral junction. Ureteral length was calculated using a graduated ureteral catheter (ureteral length obtained between 24 and 27 cm). The length was read in cystoscopy looking at the ureteral orifice while the catheter tip reached the pyeloureteral junction. The collected data were analyzed. Results: A correlation between ureteral length and height of the patients was found. The following mathematical model is able to predict ureteral length starting from the patient’s height: Result: y=0.151712487 (height expressed in cm) ± 0.12; Correlation Coeff: r = 0.973, Residual Sum of Squares: rss=5.285. No correlation was found with patient’s age and weight. Discussion and conclusion: Knowing with a good approximation the length of the ureter to be cannulated gives the possibility to choose in advance the proper one to be used. Patient’s height correlates with her ureteral length. A cost reduction can be obtained avoiding an intraoperative X-ray control. An X-ray free ureteral stentingprocedure can be described (using just ultrasound control) mainly in pregnant women.