Role of Nephrolithometric Scoring Systems in Prediction of PCNL Outcomes in Adult

The incidence of urolithiasis is approximately 5% to 10% in the general population, In an active urologic department, 30% of the surgical working load is known to be related to treatment of renal and ureteral stones (1, 2). Since the original description of stone removal through a percutaneous nephrostomy tract by Fernstrom and Johansson in 1976, percutaneous stone removal has evolved into a highly developed procedure practiced by many urologists (3). Several new techniques and technologies recently have emerged that simplified the procedure, allowed to take on more challenging cases and made it safer and less painful for patients (4).

Nephrolithometric scoring systems have been introduced to overcome limitations for systematic and quantitative assessment of the outcomes of PCNL. Moreover, preoperative patient counselling necessitates the development of an integrated scoring system to assess PCNL complexity for optimal decision-making Nephrolithometric scoring systems include the Guy's Stone Score (5), S.T.O.N. E. (Stone Size, Tract length, Obstruction/hydronephrosis, Number of involved calyces, Essence/Hounsfield units) nephrolithometry scoring system (6), The Clinical Research Office of the Endourology Society (CROES) nomogram (7), and the Seoul National University Renal Stone Complexity (S-ReSC) score (8,9). All these nephrolithometry scoring systems (NLSS) aim for preoperative prediction of stone-free status (SFS) and complications through assessment of the complexity of different cases undergoing PCNL. NLSS do not only consider the imaging criteria of stones and renal anatomy, but also relevant patient characteristics such as body mass index, previous renal surgery, and surgeon experience. The Guy's Stone Score, S.T.O.N.E. nephrolithometry score and CROES nomogram consist of 11 variables, including four shared parameters (stone size, location, number, and staghorn status). Other variables which are considered by these three NLSS are stone density, renal anatomy, tract length, obstruction of renal pelvis, case load/year, prior treatment history, and the presence of spina bifida or spinal injury.

The Guy's Stone score categorises PCNL cases into four grades, increasing in complexity from Grade 1 to Grade 4, depending on patients' past medical history and non-contrast CT (NCCT) (5).

The S.T.O.N.E. nephrolithometry scoring system assesses PCNL complexity by nine different possible scores, ranging from 5 to 13, according to five NCCT-calculated parameters including stone size, tract length, obstruction/ hydronephrosis, number of involved calyces, Essence/ Hounsfield units (6).

the CROES nephrolithometric nomogram predicts treatment success using plain X-ray of the kidneys, ureters and bladder considering the stone burden, count, and location, in addition to case volume and prior stone treatment (7).

The total score to predict the chance of treatment success is the sum of individual scores derived from each predicting variable; the higher the score, the higher the chance of treatment success, while a patient with a low score has a low chance of achieving a SFS (7). On the other hand, the S-ReSC score is calculated by counting the number of sites involved in the renal pelvis and calyces, regardless of stone parameters or renal anatomy. This system assigns a score from 1 to 9 depending mainly on the number of sites involved; the renal pelvis (1), superior and inferior major calyces (2-3), anterior and posterior minor calyces of the superior (4-5), middle (6-7), and inferior calyces (8-9).