The urethra of healthy female dogs can be normally narrowed due to the urethral flexure in retrograde CT urethrography.

Quantitative analysis of urethral size in male dogs by retrograde CT urethrography using a power injector is a recently reported technique. The aim of the current, prospective, analytical study was to apply the same method to six, healthy, intact female Beagle dogs. The proximal (P < .0001) and middle (P = .0010) urethral volumes significantly differed between the empty and distended bladder states, although no significant difference was observed in the distal volume (P = .0971). Unlike male dogs, female dogs showed two patterns of the urethral course: a straight urethra and urethral flexure. The urethral flexure was always related to intrapelvic position of the urinary bladder, and the more caudal the location of the vesicourethral junction beyond the pecten of the pubic bone, the more marked the appearance of the urethral flexure. Analysis of the urethral diameter at five sites (adopted from the previous radiographic study) was performed, and the urethral diameter showed a significant difference between the empty and the distended bladder states at sites 1 (vesicourethral junction, P < .0001), 2 (P < .0001), and 3 (P = .0244). However, there were no significant differences at sites 4 (P = .2516) and 5 (inflatable retention bulb, P = .1260). The urinary bladder may be in part intrapelvically located in clinically healthy female dogs, and urethral flexure and urethral narrowing can result from the intrapelvic location of the bladder. Narrowing of the urethra should be interpreted with caution when the pelvic bladder is identified.

Retrograde CT urethrography using a power injector quantitatively reveals effects of bladder distension on urethral size in healthy male Beagle dogs.

Quantitative analysis of the normal retrograde urethrogram is well reported in radiography, but studies on CT urethrography are lacking. Recently, a method of retrograde CT urethrography using a power injector was described. The purpose of the current, prospective, analytical study was to quantify the urethral size of five, healthy, intact, male Beagle dogs using retrograde CT urethrography and a power injector. With the injection rate of the power injector set at 0.3 mL/s, 1 mL/kg of diluted contrast medium (15 mg I/mL) was injected, and a CT examination was performed. The state of the initial urethrogram taken was defined as "empty bladder." The same procedures were repeated with the injection of an additional 1 mL/kg of diluted contrast medium until the ureteral reflux was seen (distended bladder). There was a significant difference in volumes between the empty and distended bladder, but the membranous urethra showed the least difference (P = .0044) among the three regions (P < .0001 for the prostatic and penile urethra). Urethral diameters at six sites were measured from sagittal images, and the sites of measurements were adopted from the earlier radiographic studies. The most significant difference in the urethral diameters between the empty and distended bladder occurred at the cranial and middle prostatic urethra (P < .0001). The results of this study can be useful for interpreting the results of retrograde CT urethrography. Care must be taken when narrowing is suspected at the prostatic urethra, and if necessary, further distension of the urinary bladder should be tried.