Breakthrough renal imaging makes diagnosis safer, surer

Washington--When hydronephrosis is diagnosed antenatally in an infant, is pyeloplasty needed? More often than not, the indication is not clear.

"Usually, we get into this somewhat endless loop of ultrasound, diuretic renography, pressure-flow studies, and back and forth until we can figure out what's going on-with little prognosis," said Linda Shortliffe, MD.

In addition, diuretic renography, or renal scanning, exposes children to significant radiation, noted Dr. Shortliffe, professor and chair of the department of urology at the Stanford (CA) University School of Medicine.

MRU techniques have been pioneered at Children's Healthcare of Atlanta (CHOA), Emory University School of Medicine. Their potential to revolutionize renal imaging was clear in a study of MRU follow-up in children with antenatally diagnosed hydronephrosis presented by CHOA urologists at the American Academy of Pediatrics Section on Urology annual meeting here.

Characterization of function

Infants are sedated, catheterized, and administered furosemide (Lasix) 15 minutes before contrast medium is administered. An MR physicist and a radiologist interpret the images and assess renal transit times. Transit times of more than 8 minutes indicate obstruction, whereas times less than 4 minutes indicate no obstruction. Results are equivocal with intermediate times. This is essentially a glomerular filtration rate for a single kidney.

That's very different and more precise information than renal scanning has provided before, which measures the distribution of function of both kidneys in relation to one another, Dr. Kirsch told Urology Times.

Renal maldevelopment, or dysplasia, is usually made with biopsy and histologic study, but MRU reveals details suggestive of the histologic diagnosis. The researchers discovered that renal dysgenesis, a term they used to distinguish it from the histologic diagnosis of dysplasia, was a common finding, occurring in 28% of the infants. Dysgenesis was most common in infants with multicystic dysplastic kidneys (100%) and ectopic ureter (67%). It also occurred in 63% of patients with refluxing megaureter, in 50% of those with obstructed megaureter, in 38% of those with posterior urethral valves, in 13% of those with ureteropelvic junction obstruction, and 10% of those with fetal folds.

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