Effect of Prostatic Urethra and Seminal Vesicle Morphometry on Ejaculation

Premature ejaculation (PE) is the most common male sexual dysfunction, affecting approximately 20-30% of men worldwide. Despite its high prevalence, its pathophysiology remains incompletely understood. While neurobiological and psychological factors have been extensively studied, the potential role of anatomical variations in the lower urinary tract

\- specifically the prostatic urethra and seminal vesicles - has received limited attention in the literature.

The seminal vesicles play a key role in ejaculation by contributing approximately 70% of seminal fluid volume. Previous ultrasound-based studies have suggested a possible relationship between seminal vesicle size and PE severity. However, no study to date has investigated prostatic urethral and seminal vesicle morphometry using the superior spatial resolution of multiparametric prostate MRI (mpMRI) in relation to PE.

STUDY DESIGN:

Single-center, prospective, observational cohort study conducted at Başakşehir Çam ve Sakura City Hospital Urology Clinic, Istanbul, Turkey.

PARTICIPANTS:

150 men aged 18-55 years scheduled for clinically indicated mpMRI (elevated PSA or hematospermia) will be enrolled and divided into two cohorts:

* PE Group: Men meeting ISSM criteria for lifelong PE (ejaculation within \~1 minute of vaginal penetration) or acquired PE (ejaculation within \~3 minutes of vaginal penetration), with inability to delay ejaculation and negative personal consequences. * Control Group: Healthy men without PE or any other sexual dysfunction complaint, with good ejaculatory control.

All participants must be in a stable heterosexual monogamous relationship with the same partner for at least 6 months and have normal erectile function (IIEF-15 erectile function domain score ≥26). Men using medications that may affect sexual function (SSRIs, PDE5 inhibitors) or those with hormonal disorders, major psychiatric conditions, or erectile dysfunction will be excluded.

MRI MORPHOMETRIC PARAMETERS:

The following measurements will be obtained from existing mpMRI images by the study urologists, without need for additional radiology support:

* Prostatic urethral length (mm) * Prostatic urethral angulation (degrees) * Prostate posterior-anterior and lateral dimensions (mm) * Seminal vesicle anterior-posterior length (mm) * Seminal vesicle superior-anterior length (mm) * Seminal vesicle size to prostatic urethra size ratio * Prostate size to prostatic urethra size ratio

OUTCOME ASSESSMENTS:

* Premature Ejaculation Diagnostic Tool (PEDT): range 0-20, higher scores indicate greater PE severity * Premature Ejaculation Profile (PEP): assesses ejaculatory control, distress, satisfaction, and interpersonal difficulty * Intravaginal Ejaculation Latency Time (IELT): recorded in seconds, lower values indicate greater PE severity * International Index of Erectile Function (IIEF-15): used to confirm normal erectile function and exclude erectile dysfunction * Serum hormone levels: total testosterone, TSH, prolactin * Demographic data: age, sexual abstinence duration

STATISTICAL ANALYSIS:

Continuous variables will be tested for normality using Shapiro-Wilk and Kolmogorov-Smirnov tests and expressed as mean ± standard deviation or median (min-max) accordingly. Group comparisons will be performed using Student t-test or Mann-Whitney U test for continuous variables and Chi-square or Fisher exact test for categorical variables.

Correlations between mpMRI morphometric parameters and PE severity (PEDT score, IELT) will be assessed using Pearson or Spearman correlation analyses. The primary analysis will use multiple linear regression to identify independent morphometric predictors of PE severity, with age, sexual abstinence duration, and hormone levels included as covariates. Multicollinearity will be assessed using variance inflation factor (VIF) and tolerance values.

Sample size was calculated using G\*Power software (version 3.1.9.7) with medium effect size (f²=0.15), two-sided α=0.05, and 90% power, yielding a minimum of 123 participants. 150 participants will be enrolled to account for potential dropout.

All statistical analyses will be performed using IBM SPSS Statistics (version 30.0.0.0). Statistical significance will be set at p\<0.05 (two-tailed).

No additional procedures beyond the clinically indicated mpMRI are required. The study poses no additional risk to participants.