Pevis/cortex ratio in pelviureteric junction obstruction.

With the wide spread use of routine obstetric ultrasound, the antenatal hydronephrosis (ANH) is now more commonly detected and it affects 1%-5% of all pregnancies. However, the clinical relevance of varying degree of ANH is not clear. Children diagnosed with ANH on routine obstetric ultrasound undergo serial ultrasonography and renal scan. Till date, there are no comprehensive prospective studies that determine the risk of pathology related to varying degrees of ANH and to predict the outcome of these affected renal units. Furthermore, in English literature there is lack of uniformity not only in the definition of ANH itself but also the standardized protocol as how to definitely diagnose obstruction as well as the criteria to intervene.[1] Ultrasonographic parameters and a well-tempered renal dynamic scan have been used to confirm pelviureteric junction obstruction (PUJO) and to predict the need for intervention in children.[23] Among the ultrasonographic parameters, the anteroposterior diameter and grading of hydronephrosis described by the Society of Fetal Urology are the most commonly used parameters to describe the severity of the disease and to predict the need for intervention.[14] Dewan et al. described the ratio of the depth of calyces to the thickness of the parenchyma (C/P ratio) as a predictor for surgical intervention and stressed that the estimation of pelvic volume is an insensitive marker.[5] Babu and Sai used pelvis-cortex ratio (PC ratio), dividing the maximum anteroposterior pelvic diameter by cortical thickness as a marker to predict success after pyeloplasty. To add further, the authors used the same methodology in cases of ANH to determine whether such parameters could be used as a marker for PUJO and predict the need for subsequent intervention. The authors documented that the PC ratio of less than 8 almost excluded the need for subsequent pyeloplasty, whereas a PC ratio greater than 12 definitely warranted pyeloplasty (P < 0.01). PC ratio equal or greater of 12 as maker of PUJO had a sensitivity of 92% and specificity of almost 100% with a positive predictive value of 100% and a negative predictive value of 98%.[6]

Unfortunately, most of these parameters lacked specificity and failed to stand the test of time.[7] In spite of it being noninvasive and its easy availability at affordable costs, ultrasonography is highly operator dependent. Furthermore, the assessment of pelvic diameter is likely to be affected by the level of hydration and similarly the measurement of cortical thickness will also vary from polar to midpolar region. Furthermore, most of these studies are retrospective and have comparatively smaller number of patients.[56] Because of these reasons, although invasive, a well-tempered renal dynamic scan remains the gold standard in confirming the ureteropelvic junction obstruction (UPJO).[3] The American Academy of Pediatrics laid the criteria to diagnose UPJO, which is based on the shape of wash out curve; t½ greater than 20 min. Lastly, the authors' conclusions[8] are encouraging, more and more prospective studies are needed with larger number of subjects on the same topic with similar reproducible results before it can be uniformly adopted. Till then a combination of serial ultrasound to assess the grade of ANH (more specifically cortical thinning) and a well-tempered renal dynamic scan should remain the main stay to determine when to intervene in these children.