The functional profile length (FPL) of urethra is generally assumed to reflect the length from the bladder neck (BN) to the sphincter (Sph) just before the bulbous urethra in men. We conducted a study to determine whether FPL actually represents anatomic urethral length (AUL) and to investigate factors that affect the accuracy of FPL.

The distance from the sphincter origin in the urethra to the BN was measured using a flexible urethral cystoscope with ruler (Olympus, Tokyo, Japan) in 43 men undergoing routine urethrocystoscopy for bladder cancer. And this was compared with the FPL measured from the urethral pressure profile (UPP) using Solar urodynamic equipment (Laborie, NH, USA). In the UPP trace, FUL was divided into the first half length, from the point when the pressure rises until the pressure reaches the maximum point, and the second half length, from the maximum point until the pressure is not measured. UPP traces were divided into group A and group B. Group A is a case where the first half of the trace is longer than the second half of the trace, and Group B is a case where the first half of the trace is shorter than the second half of the trace. And then we analyzed the urodynamic test results and medical records to investigate whether there were any factors that showed differences between the two groups.

The average length from the bladder neck to the center of the urethral sphincter measured with urethrocystoscopy was 3.2± 0.9cm, and the average length from the center of the urethral sphincter to the beginning of the urethral sphincter was 1.2± 0.5 cm. In the UPP trace, the length of the first half was 3.8± 1.9 cm and the length of the second half was 5.6 ± 3.2cm. From this, Group A was considered an accurate measurement, and Group B was considered an inaccurate measurement. Among 272 urodynamic reports, 58 reports were excluded. UPP was not performed in 16 cases, FPL measured in the test and FPL in the trace was different in 20 cases, and 22 cases requested after radical prostatectomy. Among a total of 214 reports, 56 reports (26.2%, 56/214) were in group A and 158 reports (73.8%, 158/214) were in group B. In group A, 12 out of 56 patients (21.4%, 12/56) were classified as neuropathic bladder, and in group B, 34 out of 158 (21.5%, 34/158) patients were classified as neuropathic bladder. At the time of examination, 8 cases in group A (14.3%, 8/26), in group B, 20 cases (12.7%, 20/158) had indwelling catheter.

Neuropathic bladder was not a confounding variable for FPL measurements. Also, urological procedure of the urethra was not a confounding variable affecting the accuracy of FPL measurement. No clinical variables showed significant differences between the two groups.

In men with lower urinary tract symptoms, FPL often does not represent the AUL well, especially the length from the beginning of the urethral sphincter to the center of the sphincter. However, the clinical variables confounding the FPL measurements are not clear. Therefore, in order to accurately determine the functional urethral length in men, it is essential to refer to the FPL trace as well as the FPL measurement.