The prone position in intravenous urography for study of the upper urinary tract.

Abstract

Listen

Translate article

Intravenous urography is usually carried out with the patient recumbent, in the face-up position. Occasionally, for visualization of anterior and posterior borders of the kidney, oblique-supine and recumbent lateral views are used. An erect anteroposterior projection is sometimes added to the routine to determine mobility of the kidneys, emptying of the renal pelves and the ureters, and possible laxity of the pelvic floor. A recumbent postero-anterior study is not commonly included in intravenous urography, although such a view can in some instances add valuable information. Urine containing the commonly used contrast materials is of higher specific gravity than non-opacified urine because of the relatively high specific gravity of the medium. Thus, 50 per cent Hypaque solution has a specific gravity of 1.32, and 76 per cent Renografin solution has a specific gravity of 1.42. Baumrucker (1) determined urine specific gravities in a series of patients just before and at a fifteen-minute collection after the intravenous injection of Diodrast. In this group urine containing the contrast medium showed an increase in specific gravity ranging from 0.007 to 0.042. Hence, during the course of intravenous urography the specific gravity of the urine varies, depending on its content of the opaque agent. In the absence of mixing, layering of the heavier, opacified urine below the less opacified or non-opacified urine occurs. The upper pole of each kidney is more posteriorly placed than the lower; thus, the superior calyces, being more dependent than the inferior calyces in the supine position, will be more readily opacified by the heavier contrast-containing urine in this position; conversely, in the prone position, the lower group of calyces are more dependent and should be better opacified. Similarly, inasmuch as the ureter cephalad to the pelvic brim lies in a plane anterior to the renal pelvis because of the normal lumbar lordosis, the prone position might afford better visualization of the ureters during intravenous urography. The layering of urine during intravenous urography has been the subject of previous reports. Fey and Truchot (3) in 1936 observed a patient with marked unilateral hydronephrosis due to an aberrant vessel, in whom the erect film demonstrated layering in the dilated calyces. In the discussion of this case, it was suggested that the layering was due to the different specific gravities of the contrast-laden urine and the non-opacified urine. Fey, however, had seen the layering persist for over an hour and he concluded that diffusion would by then have caused complete mixing had the effect been due only to a difference in specific gravity.