Predicting female ureteral length: a mathematical model

Abstract

Aim: Ureteral double J stent placement is a common urological procedure. A stent placement is performed for multiple conditions but some of them are contraindicated, mainly in pregnant female patients, because of X-rays. This work aims to suggest a mathematical model to predict female ureteral length by finding a link among different physical data. Materials and methods: Between June 2007 and July 2009, 100 female patients who had undergone ureteral stent placement were enrolled in the present study with the exception of those with septic conditions, history or evidence of TCC, congenital and acquired kidney or ureteral malformations, and previous ureteral surgery. The physical data of each patient were collected (mean age 55.8 years, range 18–89 SD 15.27, mean height 173 cm, range 160–182 SD 6.31, mean weight 75.33 kg, range 62–94 SD 8.81). A previous ureteral retrograde pyelography was performed during the procedure to individualise the pyeloureteral junction. Ureteral length was estimated through a graduated ureteral catheter with a final result between 24 and 27 cm. The length was read in cystoscopy examining the ureteral orifice while the catheter tip reached the pyeloureteral junction. The collected data were then analysed. Results: A link between the female patients’ ureteral length and height was observed. The following mathematical model can predict female ureteral length starting from the patient’s height: Result: y = 0.151712487 (height expressed in cm) ± 0.12; correlation coefficient: r = 0,973, residual sum of squares: rss = 5.285. No link was found between ureteral length and patients’ age and weight. Conclusions: A good estimation of the length of the ureter to be cannulated enables us to choose in advance the proper one to use. Female patient height correlates with ureteral length. A cost reduction can also be obtained, avoiding an intra-operative X-ray control. An X-ray-free ureteral stenting procedure can be described simply through an ultrasound control mainly in pregnant women. Further studies are needed to obtain a similar mathematical model for male patients.