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Preoperative Decision Making in UPJ Obstruction: Are MAG3 Scans Necessary?
Aron Liaw, MD, Maya Overland, MD, Andrew Phelps, MD, Ronald Cohen, MD, Laurence Baskin, MD.
UCSF, San Francisco, CA, USA.

Background: Ureteropelvic junction obstruction is the most common cause of hydronephrosis in children, and is frequently managed surgically. Typically, a patient will undergo one or more ultrasounds prior to surgery, as well as one or more nuclear renograms (MAG3). MAG3 requires an IV and bladder catheter in young children, however, and can be poorly tolerated. We investigate our series of high grade hydronephrosis to look at preoperative workup of these patients. We hypothesise that the decision for surgery has little correlation with MAG3 findings.
Methods: Ultrasound reports over a 25 year period were reviewed for UPJ obstruction and ‘severe’ or ‘Grade 3’ or ‘Grade 4’ hydronephrosis. Patients identified were reviewed for management, imaging, symptoms, and outcomes. Patients were excluded if they did not have a UPJ obstruction diagnosis or if they had surgery but no preoperative images available. Regression analyses were performed to identify the key factors in preoperative decision making, as well as the relationships between renal function, obstruction status, ultrasound and clinical findings.
Results: 208 patients were identified. Most patients had close to equal renal function, with only 11% of patients having function less than 30%, and no patients showing significant loss of function on serial MAG3 scans. Renal function and T_1/2 did not affect the chance of surgical intervention. The biggest predictor of intervention was renal size (p=0.008). Renal size also independently predicted obstruction status (p=0.001), while renal function was predicted by the presence of parenchymal thinning on ultrasound, as well as the age at diagnosis (p=<0.001). A table of renal lengths by age that correspond to a particular chance of obstruction was constructed. The odds ratios of preoperative imaging and clinical factors determining surgical intervention were plotted on a Forest plot.
Conclusions: In patients with high grade hydronephrosis, we find that most kidneys with UPJ obstruction show close to normal function but are obstructed. Significantly reduced function is rare. There is no statistical correlation between renal function and surgical intervention. Relative renal size on ultrasound is the strongest predictor of both obstruction and of surgical intervention. A postnatal diagnosis and the presence of parenchymal thinning on ultrasound significantly correlate with poorer renal function. We suggest that routine preoperative MAG3 scan is not necessary, and should be used selectively. We find that in most cases, the information in a MAG3 scan can be determined through ultrasound and clinical findings.

	Renal Length Variations from Mean for Age (cm)
Chance of Obstructed Status with UPJ Obstruction			56%	61%	68%	74%	80%
Age		Normal	1 SD	2 SD	3 SD	4 SD	5 SD
0m		4.48	4.79	5.1	5.41	5.72	6.03
2m		5.28	5.94	6.6	7.26	7.92	8.58
6m		6.15	6.82	7.49	8.16	8.83	9.5
10m		6.23	6.86	7.49	8.12	8.75	9.38
1.5y		6.65	7.19	7.73	8.27	8.81	9.35
2.5y		7.36	7.9	8.44	8.98	9.52	10.06
3.5y		7.36	8	8.64	9.28	9.92	10.56
4.5y		7.87	8.37	8.87	9.37	9.87	10.37
5.5y		8.09	8.63	9.17	9.71	10.25	10.79
6.5y		7.83	8.55	9.27	9.99	10.71	11.43
7.5y		8.33	8.84	9.35	9.86	10.37	10.88
8.5y		8.9	9.78	10.66	11.54	12.42	13.3
9.5y		9.2	10.1	11	11.9	12.8	13.7
10.5y		9.17	9.99	10.81	11.63	12.45	13.27
11.5y		9.6	10.24	10.88	11.52	12.16	12.8
12.5y		10.42	11.29	12.16	13.03	13.9	14.77
13.5y		9.8	10.55	11.3	12.05	12.8	13.55
14.5y		10.05	10.67	11.29	11.91	12.53	13.15
15.5y		10.93	11.69	12.45	13.21	13.97	14.73
16.5y		10.04	10.9	11.76	12.62	13.48	14.34

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