"stoneless" or Negative Ureteroscopy: A Reality in the Endourologic Routine or Avoidable Source of Frustration? Estimating the Risk Factors for a Negative Ureteroscopy

Introduction: A "Negative" ureteroscopy (URS) is defined as a URS in which no stone is found during the procedure. It may occur when the stone has already been passed spontaneously or when it is located outside the collecting system. The aim of the study was to outline risk factors for Negative-URS. Materials and Methods: We retrospectively analyzed the possible risk factors for Negative-URS from a database of 341 URS cases. In every case where presumptive ureteral stone was not found, a formal nephroscopy as well as a whole collecting system revision was completed. The Negative-URS group was compared with the non-Negative-URS group, in terms of patient and stone characteristics. Results: The database of 341 URS cases included 448 different stone instances, of which 17 (3.8%) were negative and 431 (96.2%) were therapeutic. There was no statistical significant difference between the two groups concerning age, body mass index, stone location in the ureter, stone laterality, and whether the patient was prestented. The stepwise multiple logistic regression revealed three important risk factors, namely CT stone surface area (p < 0.0001), radiopacity of the stone at kidney, ureter, and bladder radiograph (KUB; p = 0.0004), and gender (p = 0.0011) with an area under the curve of 0.91. Women were found to have more possibilities to have a negative procedure by four- to sevenfold than men depending on the model. A nonradio-opaque stone at KUB is more likely to be correlated with a Negative-URS by 9.5- to 11-fold more than a radiopaque stone at KUB. For each increase of 1 U in CT stone surface area, there is an increase of 10%-12% to be non-negative. Conclusions: Female gender, a nonradio-opaque stone at KUB, and a smaller stone surface were statistically significantly different in the Negative-URS population.