symptomatic supravesical obstructive uropathy in a patient with dual functioning kidneys is classically characterized by bilateral hydroureters / hydronephrosis and an empty urinary bladder . this obstruction may be secondary to metastatic abdomino - pelvic and retroperitoneal malignancies , ureteric calculi and retroperitoneal fibrosis [ 25 ] . the evidence for obstruction may be partially or totally absent on ultrasound or computerized tomography , in one or both kidneys [ 68 ] . our recent experience with a uraemic 56-year - old caucasian showing only unilateral moderate right - sided hydronephrosis is presented . a 56-year - old caucasian male patient with a past medical history that included hypertension and coronary artery disease and a recent serum creatinine of 88.4 mol / l , was diagnosed 10 days earlier with urinary tract infection ( uti ) . two days before presentation to us , he developed worsening anorexia , nausea with vomiting and oliguria . his father had prostate cancer and died at age 75 years from colon cancer ; a sister had breast cancer and a maternal uncle had throat cancer . physical examination revealed a blood pressure of 165/89 mmhg , pulse rate of 56/min and respiratory rate of 16/min . he was not dehydrated nor orthostatic . except for trace ankle oedema and bilateral costo - vertebral angle punch tenderness , mol / l , co2 14 mmol / l and potassium 5.5 mmol / l . urinalysis showed 510 wbc per high - power field ( phf ) and 25 rbc phf . alanine aminotransferase ( alt ) , aspartate aminotransferase ( ast ) and total creatine kinase ( ck ) levels were normal . a post - void urinary bladder scan had demonstrated only 60 ml of residual urine . a renal ultrasound showed unilateral moderate right - sided hydronephrosis with suspected mass effect on the inferior urinary bladder . the left kidney appeared normal , measuring 16.2 cm  8.1 cm , with preserved cortical thickness . the next day , with increasing vomiting , serum creatinine 894.6 mol / l , phosphorus 2.6 mmol / l , potassium 6.2 mmol / l and oliguria ( table 1 ) , he started daily haemodialysis . a non - contrast computerized tomography examination , on day 2 , again showed unilateral right - sided hydronephrosis , bilateral nephric stranding and urinary bladder wall thickening suspicious for transitional cell cancer ( figure 1 ) . cystoscopy , on day 3 , revealed a sessile urinary bladder tumour , which was resected . the right ureter was successfully cannulated and a right ureteric stent was placed with prompt urine drainage . the next day , with a strong push from nephrology , the patient consented to a percutaneous left nephrostomy procedure despite the normal appearing left kidney . a percutaneous left nephrostogram revealed a previously unrecognized mild hydronephrosis / hydroureter with obstruction at the ureterovesical junction . the pathology report revealed high - grade urothelial carcinoma , grade 3 of 3 , with invasion of the muscularis propria . a patient with dual functioning kidneys presenting with uraemic symptoms and suspected to have obstructive uropathy must be presumed to necessarily have bilateral renal obstruction [ 610 ] . this is without prejudice to the findings on conventional renal imaging with ultrasound or computerized tomography [ 3,610 ] . there are false negative tests with these imaging modalities , the so - called syndrome of  non - dilated obstructive uropathy or non - dilated obstructive nephropathy [ 610 ] . clinical conditions associated with the absence of hydronephrosis on ultrasound and computerized tomography despite obstructed kidney(s ) include acute early obstruction , the presence of retroperitoneal fibrosis or infiltrative metastatic abdomino - pelvic cancers , dehydration or septic shock and severe oliguria [ 210 ] . our patient was not dehydrated and was not hypotensive but was severely oliguric ( table 1 ) . we note that we did not rule out the presence of retroperitoneal fibrosis in our patient . the classic picture of bilateral hydronephrosis with hydroureters and an empty urinary bladder , in symptomatic uraemia following supravesical obstruction , in patients with dual functioning kidneys , is well acknowledged . however , the presentation of new - onset symptomatic uraemia concurrent with only unilateral hydronephrosis / hydroureter on conventional imaging ( ultrasound , computerized tomography ) should raise the plausibility of non - apparent obstruction of the contra lateral kidney . in such instances , the more sensitive albeit invasive percutaneous nephrostogram of the apparently normal appearing kidney is therapeutic and will lead to greater renal salvage [ 68 ] . we would like to remind practicing providers that symptomatic uraemia presenting in the setting of suspected obstructive uropathy must be assumed to imply bilateral renal obstruction , regardless of the results / interpretations of any form of conventional renal imaging . therefore , necessarily , every attempt to decompress both kidneys must be the rule . this approach would result in early and improved renal salvage . left undiagnosed and therefore untreated , this potentially reversible cause of renal failure can lead to irreversible renal failure if bilateral , , or to significant residual loss of renal function if missed on one side only . we note that we were not able to carry out any split renal functional testing after recovery as the patient 's primary attention at this point was to find out treatment options for his cancer .
bilateral hydronephrosis is classic for supravesical obstructive uropathy causing uraemia with dual functioning kidneys . recently , a patient presented with uraemia and metastatic urinary bladder carcinoma but only unilateral right - sided hydronephrosis . 
 a right ureteral stent was placed retrograde and no further intervention was planned since the left kidney appeared normal , and since the left ureteric orifice was not visualized . 
 we insisted on a left percutaneous nephrostomy which was successful with prompt urine return . 
 a left nephrostogram revealed unrecognized hydroureter / hydronephrosis . 
 following haemodialysis , kidney function normalized at 3 weeks . for symptomatic 
 uraemia from obstruction , an antegrade and/or a retrograde decompression must be attempted bilaterally to improve renal salvage .