Compression Saline Hydration and Furosemide

There is also variation in use of a variety of other maneuvers designed to improve renal collecting system and ureteral distention and opacification. Because abdominal compression has long been successfully used during EU, a number of researchers have advocated its use during CTU (10,12,37-39). During MDCTU, compression is often applied at the time of contrast material injection. Compression excretory-phase images are then obtained through the kidneys, followed by compression release and acquisition of a second series of excretory-phase images performed, at the least, through the middle and distal portions of the ureters.

Although a few studies have suggested that the use of compression is beneficial (27,37,39), only one actually directly compared compression CT images with noncompression CT images (27). The others instead compared compression-CT opacification with opacification obtained during EU performed on the same patients (37,39). In the study that utilized only CT images (27), compression produced only a slight but significant improvement in distention of the renal calices, infundibula, pelves, and proximal ureters when compared with postcompression-release images through these structures; however, there was no significant improvement between compression images and images obtained in a group of patients in whom no compression was ever applied. Further, this study was not designed to determine whether the slight advantage of abdominal compression would improve detection of upper-tract pathology. In fact, a more recent series from the same group has suggested that sensitivity in detecting urinary tract abnormalities is not improved on excretory-phase CT images performed with abdominal compression (40).

As an alternative to using compression for increasing renal collecting system and ureteral distention, several investigators have chosen to hydrate patients orally or with a 100mL (29) or 250mL (13,16,27,28) intravenous bolus of normal (0.9%) saline administered immediately prior to or following contrast material injection. Thus far, only use of the larger intravenous volumes appears to be beneficial to any extent. One study found distal ureteral opacification to be significantly improved when patients received precontrast material injection hydration with 250 mL of saline (compared to a control group) (13). However, there were no opacification advantages in other portions of the urinary tract. Another study found that patients hydrated with 250 mL of saline (administered between contrast material injection and excretory-phase scan acquisition) demonstrated small but significant improvements in upper urinary tract opacification, compared with patients who did not receive saline (27). In comparison, another study did not find hydration with 100 mL of saline to be of any benefit (29).

Finally, it has been suggested that using a small dose of an intravenous diuretic improves urinary tract visualization to the greatest extent. Two groups administered 10 mg of intravenous furosemide three to five minutes before contrast material administration for CTU (11,41). One group found that using furosemide during CTU resulted in near-complete or complete opacification of all 32 imaged renal collecting systems and of 30 imaged ureters, as well as in a more accurate depiction of the pelvicaliceal system (in comparison with CTUs performed with saline hydration) (11). Another group noted that lower and distal ureteral opacification was significantly better in 26 patients who received intravenous furosemide and saline hydration compared with lower and distal ureteral opacification in 35 patients who received saline hydration alone (41). Interestingly, in this study, there was no significant difference in opacification between the patients who received furosemide and saline hydration and another group of 26 patients who received furose-mide alone (without saline hydration).

The use of furosemide has a few potential drawbacks. At most institutions, a physician is responsible for administration of this agent (and must specifically order that this agent be administered to every patient referred for CTU, as well as be directly available whenever a CTU examination is being performed with furosemide). Also, patients become extremely uncomfortable soon after furose-mide administration (due to rapid bladder distention) and they may need to get off the scanner quickly to go to the bathroom before all image acquisition has been completed.

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