Obstructive Index in antenatal unilateral pelviureteric junction obstruction: A novel predictor of failure of conservative management.

BACKGROUND To find the impact of obstructive index (OI) as a predictor of management in antenatal pelviureteric junction obstruction (PUJO). METHODS Records of 135 cases of antenatally detected unilateral PUJO, selected for initial observation were retrospectively analysed. All patients who underwent pyeloplasty on follow up were put in Group A. Those patients who were still on conservative management were put in Group B. Pelvic anteroposterior diameters of the affected [PAPD(A)] and normal kidney [PAPD(N)] of the same patient, along with the cortical thickness of the affected [CT(A)] and normal kidneys [CT(N)] on postnatal ultrasound scan and the T1/2 of the affected [T1/2 (A)] and normal kidneys [T1/2 (N)], the differential renal function (DRF) and shape of curve on diuretic renogram had been noted for each patient at 6 weeks. OI was defined as {PAPD(A) X T1/2 (A)} / {PAPD(N) X T1/2 (N)}. RESULTS The median duration of follow up was 55 months (36 - 110). Median age at surgery was 12 months (4 - 80). Group A had 30 patients with 105 in Group B. On multivariate analysis, OI and shape of curve predicted need for surgery with statistical significance. Median OI in Group A was 18.9 compared to 4.82 in Group B (p<0.001, Mann- Whitney). Using ROC analysis, area under curve for OI was 0.95. A value of 12.2 could predict failure of conservative management with a sensitivity of 93.3% and a specificity of 92.4%. CONCLUSION The OI can reliably predict the need for surgery, at a very early stage, thus avoiding repeated tests and saving time.