The primary purpose of the treatment of urinary system stone disease is to provide minimal morbidity and maximum stone-free rate. The treatment of kidney stones significantly changed in the last 30 years. The treatment options have diversified as percutaneous nephrolithotomy (PNL), shock wave lithotripsy (SWL), and RIRS, which are less invasive than open surgery [11]. The use of RIRS particularly has been increasing in the treatment of upper urinary system stones day by day. Having less complication rates compared to PNL and having higher stone-free rates compared to SWL are the most significant reasons of why this method is frequently used [12, 13]. However, the fact that the flexible ureterorenoscopes and the equipments used in RIRS are expensive and sensitive, it is important to select the appropriate patient. Besides, the results should be predictable in order to meet the expectations of the patients and plan the surgical method [14].
With the development of minimal invasive surgical techniques, scoring systems were produced to predict the success and complication rates. For RIRS, Resorlu-Unsal stone score (RUSS) predicting the stone-free rate was defined by Resorlu et al., for the first time in literature in 2012. In RUSS, the parameters of stone size, stone location and infundibulopelvic angle (IPA), stone number and presence of abnormal anatomy are assessed [7]. In another scoring system, the R.I.R.S. scoring system, the parameters are stone density, IPA, infundibular length (IL), stone length and stone localization [8]. On the other hand, in S.T.O.N.E. (Stone size, Tract length, Obstruction, Number of involved calyces and Essence or stone density) nephrolithometry scoring system, the parameters of stone size, number of involved calyces, tract length, obstruction/hydronephrosis and stone essence are assessed. Different from the others, the T.O.HO. score can be used for both ureter and kidney stones [9]. In all the scoring systems, the stone-free rate is decreased with increasing score.
The T.O.HO. score was validated in a recent study by Polat et al. The modified T.O.HO. score was defined by adding stone volume to the parameters of the T.O.HO. score. In this study, modified T.O.HO. score was shown to predict the RIRS success better than the original version [15].
The T.O.HO score is a simple scoring system defined by Hori et al., in 2020 as a result of the retrospective analysis of 586 patients with kidney and ureter stones who underwent RIRS. It consists of three parameters; stone length (Tallness) (1-5 point), stone localization (Occupied lesion) (1-3 point) and stone density (Houndsfield unit evaluation) (1-3 point). Therefore, the patients are scored between 3 and 11 points. As the score increased, RIRS success decreased. Here, success was defined as having no residue stone in postoperative first month. The stone-free rate was 80.2% [10].
It was concluded in the present study that the T.O.HO. score was easily applicable. It already consists of simple parameters we take into consideration in our clinic practice. All the parameters can easily be assessed through preoperative CT. In this study involving 581 patients, we aimed to assess the findings of Hori et al., and to validate the T.O.HO. score. We revealed that the T.O.HO. score is a stone scoring system that predicts the RIRS success with a high rate of accuracy.
With its some characteristics, the T.O.HO. score has some advantages compared to the other scoring systems. Firstly, it is seen that the predictive quality of the T.O.HO. score is better than S.T.O.N.E score even though it uses fewer parameters than S.T.O.N.E. score in the internal validation carried out by Hori et al., (respectively, AUC=0.833, AUC=0.633). Besides, the IPA assessed in RUSS and R.I.R.S. scoring systems can only be assessed through CT urography, whereas non-contrast CT is sufficient in the assessment of T.O.HO. score parameters.
There are several limitations of the present study. These limitations are that the study were designed retrospectively, the present study reflects the results of a single center and the operations performed by 3 surgeons, and the number of patients with preoperative stent was great. Nevertheless, we think that our study validating the T.O.HO score will contribute to the literature.