# A New Technique for Computed-Tomography Urethrography in Males: The Clamp Method
## 4 Discussion  
The introduction of contrast in RUG was first done using clamp devices coupled to a syringe (Knutsson clamp, Brodney clamp). These were replaced by the McCallum technique using a Foley catheter, but the drawbacks of this method are that it can cause pain on inflation of the balloon and it is not useful in cases with urethroneatal alterations, nor can anesthetic gel be used or contrast introduced very accurately (risk of balloon leakage) [2,6]. The technical difficulty with performing CT-RUG with a Foley catheter may be the cause. However, there are only 2 studies in which CT-RUG and CT-VCUG were done simultaneously to evaluate anomalies of the posterior urethra [4,11]. The first, by [PERSON] et al. [4], evaluated urethral distraction defects after blunt pelvic trauma in 21 males; the bladder was filled through a suprapublic catheter (with which the patient was fitted) to achieve a full bladder sensation, after which they performed retrograde infusion of contrast (technique not specified) and combined retrograde and voiding CT. In the second study, [PERSON] et al. [11] evaluated posterior urethral structures in 21 males; the bladder was filled with contrast via an infusion system connected to the suprapublic catheter (with which the patient was fitted) and the anterior urethra using a Foley catheter (after inflating the balloon with 2-3 mL of serum in the fossa navicularis), after which they performed the combined retrograde and voiding CT (3 s after the patient started to void). To our knowledge, the present study is the first to evaluate the utility of CT-RUG for stenosis of the anterior urethra (bulbar or penile). It reports an accuracy similar to RSUG and greater than RUG for measuring the length of strictures. In the 2 cases with urethroplasty the CT was also better than the other techniques for visualizing stenosis in the tortuous track of the plasty. The advantage of CT over urethrography is that it can evaluate periurethral structures and locate stenosis with greater anatomical accuracy. The advantage over RSUG is that CT has a complete field of view (FOV), whereas measuring stenotic segments longer than 3 cm means resorting to a panoramic ultrasound image, which may distort the measurement as it is particularly operator-dependent (Figure 4). CT-RUG was performed in two studies in male Beagle dogs [12,13]. In the first both CT-RUG (using an 8 Fr Foley catheter) and CT-VCUG were done in the dogs (\(n=18\)) following urethroplasty of the anterior urethra and it was seen that CT is more accurate than urethrography for anatomical location and evaluation of the anomalies [12]. In the second study (\(n=5\)) CT-RUG was performed using a 6 Fr Foley catheter and a 200 mL syringe connected to a power injector, which made manual injection in the CT room unnecessary, and 3D anatomical images were produced of the male urethra in healthy dogs [13]. In the present study, CT-RUG was done successfully in all the cases; there was no need for manipulation of syringes or the presence of the operator in the room as drip infusion was used for the introduction of contrast. The amount of pain recorded by the patients for catheterization and external compression of the B-Ring was none or very mild. Although the clamp method can be done in cases with urethroneatal alterations ( stenosis, hypospolarias, meatotomy), when the ballooness fine probe is introduced through the anomaly the B-Ring exerts external compression just behind the corona of the glans penis, which is why the 2-4 cm of the distal urethra (inside the glans) is not visualized in the retrograde study, where the distended penile urethra is observed beyond the balanoprepucial sulcus. In the present study, the urethroneatal anomalies were visualized by VCUG, and during micturition contrast was seen to flow through the hypospadic orifice or the meatal stenosis (with prestenotic dilatation). Future studies are needed with CT-VCUG to analyze its capacity to visualize urethroneatal anomalies.