MERCAPTO-ACETYLTRIGLYCINE (MAG-3) RENOGRAPHY AND INDIRECT RADIONUCLIDE CYSTOGRAPHY IN POSTERIOR URETHRAL VALVES

Objective To assess dynamic isotope renography with Tc-99m-labelled me rcapto-acetyltriglycine (MAG 3) in conjunction with indirect radionucl eide cystography (IRC) in the follow-up of boys with posterior urethra l valves. Patients and methods Fifty-one boys (95 renal units; mean ag e = 89 months, range 65-118) with previously treated posterior urethra l vales underwent MAG 3 renography followed by IRC. Glomerular filtrat ion rate (GFR) was estimated from the plasma clearance of Cr-51-ethyle nediamine tetra-acetic acid following single intravenous injection. Re nographic parameters noted were renal function based on the quality of renal visualization and background activity as well as renal drainage and the appearance of isotope in meter and bladder. Following the dyn amic 20 min MAG 3 renogram the child was allowed to leave the departme nt and to return when he wished to void. IRC was then performed. Diure tics were not administered. Results Initial drainage from 30 kidneys w as normal, in 36 drainage was delayed and in 25 drainage did not occur during the renogram phase. In four kidneys function was so poor as to preclude assessment. After the IRC, drainage was noted in 17 of 25 un its which had not drained during the renogram, six units did not drain and in two drainage was equivocal due to the presence of vesico-urete ric reflux. The quality of the scan was good or very good in 42 patien ts (mean GFR = 92 ml/min/1.73 m(2) SA) and moderate or poor in nine pa tients (median GFR = 20 ml/min/1.73 m(2) SA) (P < 0.001). A residual u rine was noted following micturition in 35 boys; this was due to incom plete bladder emptying in 14 and to immediate secondary refilling from dilated upper tracts in the remainder. Conclusion IRC in conjunction with traditional dynamic renography using MAG 3 provides valuable addi tional information about upper tract drainage. The necessity for diure sis renography is obviated in the majority of patients. IRC also allow s an excellent non-invasive, physiological assessment of both upper an d lower urinary tract function which is superior to conventional singl e examination techniques. We recommend the use of MAG 3 with IRC in th e routine follow-up of boys with posterior urethral valves.