Posterior urethra: Anterior urethra ratio in the evaluation of success following PUV ablation

SummaryIntroductionThere are conflicting reports on the criteria with which to determine success following posterior urethral valve (PUV) ablation. The aims of this study were to assess the value of the posterior urethra: anterior urethra ratio (PAR) in predicting successful PUV ablation.Materials and MethodsAll neonates and infants with confirmed PUV on voiding cystourethrogram (VCUG) were included. Initial PAR was computed by dividing maximum posterior urethral diameter by anterior urethral diameter. Distances were measured by an on-screen distance measurement tool in the Radiology department, to avoid error. Only oblique images with good voiding phases were used for assessment. All patients underwent cystoscopy and PUV ablation using cold knife. Postoperative VCUG and cystoscopy were performed at 3 months follow-up. Success was defined as cystoscopic resolution of obstruction, in addition to biochemical and radiological improvement, and this was compared with PAR findings. An equal number of age-matched control patients who had a normal VCUG (as a part of evaluation of antenatal hydronephrosis) were also analyzed.ResultsA total of 56 patients (median age 15 days, range 3-250 days) were analyzed between 2013 and 2016. The mean PAR was 1.5 (0.42) in controls and 3.42 (0.75) in those with PUV at diagnosis (P = 0.001). In those with successful PUV ablation (n = 51) the mean PAR was 1.8 (0.21), and in those with residual PUV/stricture (n = 5) the mean PAR was 3.16 (0.54). The difference between these two groups was statistically significant (P = 0.0001). Applying the value of mean + 2 SD of successful PUV ablation, an upper limit of PAR >2.2 was proposed to predict failure. Using this cut-off, 4/7 with PAR >2.2 had confirmed failure, while 48/49 with PAR <2.2 had successful resolution (P = 0.001)ConclusionWhenever the posterior urethra is more than 2.2 times the diameter of the anterior urethra (PAR >2.2) on repeat VCUG following a PUV ablation, a cystoscopy check is essential to rule out residual PUV/stricture.758Figure. The posterior urethra: anterior urethra ratio (PAR) was computed by dividing the maximum posterior urethral diameter by the anterior urethral diameter (in mm). Distances were measured by an on-screen distance measurement tool in the Radiology department, to avoid error. a) Normal VCUG - control: PAR = 6.02/4.85 = 1.24; b) PUV at the time of diagnosis: PAR = 12.7/3.3 = 3.84; c) successful PUV ablation: PAR = 5.32/4.62 = 1.15; d) persistent obstruction due to stricture or residual valve: PAR = 7.11/1.94 = 3.66.