# A New Technique for Computed-Tomography Urethrography in Males: The Clamp Method
## 4 Discussion
Some studies report the usefulness of CT-VCUG for evaluating the bladder and posterior urethra [5,9,10]. [PERSON] et al. [9] in a study of 13 males with traumatic antecedents reported the diagnostic potential of 3D CT-VCUG after intravenous (i.v.) administration of iodinated contrast. [PERSON] et al. [10] described 3D and 4D CT-VCUG after i.v. the contrast in 70 healthy subjects (43 males and 27 females) using 640-slice dynamic volume CT. Two studies using CT-VCUG [5,9] took a mean time of 8.8 and 9 min (range, 4-20 min) and another performing combined retrograde and voiding CT [11] took a mean time of 10 min(range, 6-20 min). The mean time for CT-RUG in our study was 6.1 min (range, 4.7-7.7 min) and it must be remembered that a lot of this time was spent by the nurse performing the clamp method because the CT technique and cystourethral filling with contrast were quick. The method described in the present study may enable future CT-VCUG studies to be done with retrograde bladder filling, as the bottle of contrast is positioned 2 m from the floor, which means there is sufficient pressure for rapid bladder filling and avoids i.v. administration of contrast to performing CT-VCUG. As for the dose of radiation received by the patient, which is one of the main drawbacks of CT, the mean was 4.96 mSv in our patients with 2 sweeps and 3.456 mSv in those with one sweep, whereas the mean effective dose in the CT-VCUG study [10] was 6.585 mSv, which is in line with the International Commission on Radiological Protection requirements. One of the advantages of urethrography over CT-RUG is that it is a dynamic study that allows filling of the urethral alterations to be visualized in real-time. Moreover, the effective mean dose obtained on urethrography was 0.67 mSv, which shows significantly greater irradiation of CT-RUG than with fluoroscopy. This is why CT is not recommended in males of childbearing age and why nine cases with reproductive plans were excluded from the study (because of the risk of gonadal irradiation); it is also why the study patients were aged over 50 years. In our opinion, further studies are necessary to adapt the CT protocol to lower doses of radiation. There is little published on periurethral fistulas, in which the relevance of CT-UG for diagnosis is reflected [5; 14; 15]. [PERSON] et al. [5] performed CT-VCUG in 80 patients (58 males and 22 females) after bladder filling by suprapublic catheter infusion (or retrograde); of the 58 males with posterior urethral structures with fistulas a higher number was visualized by CT (\(n=51\)) than by urethrography (\(n=34\)), such that the fistula detection rate of CT-VCUG was higher than that of urethrography (87.9% vs. 58.6%; \(p=0.015\)). In our study, CT-RUG enabled the fistulous tracts to be visualized in all the cases (\(n=8\)), whereas only five cases were visualized by urethrography. Although CT-VCUG was not done in our study, retrograde filling of the urethra and bladder with a mean of 90 mL of contrast allowed us to visualize fistulas of the bladder and posterior urethra, which shows the diagnostic potential of this technique to detect periurethral fistulas without the patient having to micturate. One of the limitations of the study is the low number of cases (\(n=22\)), though it must be remembered that 12 cases were excluded and that it was difficult to include more cases in a threee-year period because it was not an extended technique. Another limitation is that no surgical correlation was made in all the cases, because except for those with urethral fistulas and some with stenosis of the anterior urethra the rest had no posterior unrological intervention (except dilations). A further limitation is that cases with stenosis of the posterior urethra were not included, because as occurs with VCUG we would have had to perform CT-VCUG in order to visualize adequate distension and evaluate posterior urethral strictures (due to the external sphincter stopping the passage of contrast during micturition).