Urethra is an important access to the urinary tract for urological procedures especially endourological procedures. Therefore, its health including length is of utmost importance in this era of rapid advancements in endourology. A good understanding of the length of the male urethra is crucial, as urologists sometimes rely on the calibration of the male urethra to evaluate the extent of a lesion or obstruction in the urethra [4]. Accurately assessing the normal length is therefore paramount, as it provides an idea of the location within the urethra. The length of the penis has little impact on the ability to access the prostate gland through the urethra, as the resectoscope can be manipulated to navigate around any anatomical structures. However, a longer urethra can make procedures like transurethral resection of the prostate or bladder tumour more challenging if the instrument is significantly shorter than the urethral length and may require specialized techniques or equipment like extra-long resectoscopes. The length of the urethra can therefore be important in planning treatment for medical conditions [4].

Despite its significance, there is limited data on the average length of the urethra in adult males generally and in different populations. With an extensive literature search, there is a scarcity of information on this subject as only two studies have documented urethral length in adult males before. One of the studies was amongst American men [3] while the other was amongst the Indian adult male population [4]. As none exists yet for Africans, this study aimed to provide additional information on this topic by measuring the urethral length in a sample of adult Nigerian males.

Various urethral and penile pathologies can affect the urethral length. Acquired pathologies such as urethral strictures and acquired hypospadias as well as congenital problems like hypospadias, epispadias and micropenis can reduce the available length of the urethra. Likewise, surgery like urethroplasty especially the anastomotic type where a segment of the urethra is excised will reduce the urethral length. Patients with these pathologies were excluded from our study so as not to distort our findings.

Several techniques are available for evaluating urethral length, but none have been established as the definitive standard. The initial approach to measuring urethral length involved direct dissection and measurement by Sir Henry Gray, resulting in a range of 18 to 20 cm. Although this method yields precise measurements, its limitation lies in the fact that it involves cadavers and this direct measurement is not practically feasible. Indirectly, urethral length can be measured using retrograde urethrogram and micturating cystourethrogram but the measurement is usually affected by the degree of magnification as well as the angle at which the X-ray focuses on the urethra. Magnetic Resonance Imaging (MRI) is usually used to evaluate lesions and diseases of the urethra but MR images do not capture the proximal sections of the prostatic urethra and distal penile urethra unless a Foley catheter is utilized for visualization [10]. This method is also expensive. A practical method is the use of a urethral catheter as described in this study. This method was utilized solely in the Indian study while most of the patients in the American study had this method used in their estimation. Alternatively, urethral length was established at the time of flexible cystoscopy upon removal of the cystoscope. The scope was held fixed at the bladder neck with the penis on stretch and the cystoscope was similarly marked with tape at the end of the penis. The cystoscope was then removed and the distance from the mark to the end of the cystoscope was measured in centimetres [3].

Our study of 450 subjects found that the average length of the urethra in adult Nigerian males is 21.3 cm ± 2.59 with a range of 16.5 to 28.0 cm. This is longer than the average urethral length of 17.55 cm reported amongst Indian adult men [4]. This translates to a difference of 3.69 cm in the urethral length between the two races. A possible explanation for this difference may be the age and pathology differences in the study population between these two studies. While the majority of the patients in our study had retention secondary to either benign prostatic enlargement or prostate cancer, the majority of patients in the Indian study were younger than 50 years of age and therefore with a lower incidence of prostatic diseases. Since prostatic enlargement will increase the length of the posterior urethral which also contributes to the total length of the urethra, this could have partially contributed to this difference. However, we do not think that this is sufficient to explain the difference as our data did not show any significant difference in urethral length between younger and older men in this present study. It might therefore mean that there is a racial difference in urethral length.

On the other hand, the urethral length in this study is slightly lower than reported by Kohler et al. [3] among American men where the average length was 22.3 cm which is approximately 1 cm longer than reported in our study. The exact reason for this difference may not be clear but a subtle difference in methodology might be contributory. In the American study, a gentle stretch was applied to the penis on the catheter before measurement on the catheter was undertaken [3]. In addition, subjectiveness like stretching may also distort the findings on measurement. Unlike what they did, we avoided stretching the penis in our patients before measurement because we believe that the stretching of the penis may lead to an overestimation of the urethral length because of the elastic nature of the penile tissue.

The total length of the urethra is made up of individual lengths of the prostatic, membranous, bulbar and penile urethra [1]. The differences in total urethral length may also result from differences in the penile length with corresponding differences in penile length between different races [11]. This study may be another one supporting Rushton’s theory that penis length is greatest in Negroids, smaller in Caucasoids and smallest in Mongoloids [11]. However, the figure documented in the work of Kohler et al. [3] did not support this theory as the length of the urethra was greater than reported in this study made up of the black population. Again, the stretched penile length used in that study might be a factor responsible for this amongst others. Furthermore, the study did not document the racial composition of the study group. These differences may, however, not have any significant clinical implications, but they could be valuable for understanding the anatomical differences between these populations. Further research may be needed to explore the potential factors contributing to these differences and their clinical implications.

From this study, the average usable length of most of the catheters currently in use in the Nigerian market is 30.01 cm. This is the length from the neck of the inflated balloon to the ‘Y’ junction of the catheter. This is at least one and a half times longer than the average length of the urethra obtained in this study. This means there is a need to perhaps customize the catheter and other instruments for our population. The average unused catheter length, i.e., the length between the tip of the penis and the ‘Y’ junction of the catheter, was 8.97 cm in this study. Customised catheters may be desirable to avoid wearing too long a catheter difficult or cumbersome to pack.

Our study did not reveal any significant relationship between the urethral length and age in adult male Nigerians. This further corroborates the findings in the study by Kohler et al. [3] which showed that there is no significant difference in urethral length between adult males of different ages. The growth and development of the male urethra occur primarily during foetal and childhood development [12]. It seems that the length of the urethra is primarily determined by genetic factors and is relatively consistent across individuals of the same race and ethnicity. It appears that once an individual reaches adulthood, the urethra is fully formed and is unlikely to change significantly in length.

Like other studies, there is no statistically significant correlation between urethral length and anthropometric parameters in our study. However, it should be noted that subjects in extremes of height, weight and BMI comprise only a small subset of the patients recruited in this study [3, 4]. The weight and BMI positively correlated while the height negatively with the urethral length but were not statistically significant. Again, the lack of a significant correlation between urethral length and BMI, height, or weight is likely because urethral length is primarily determined by genetic factors. While there may be slight variations in urethral length between individuals, this study has demonstrated that these variations are unlikely to be influenced by external factors such as BMI, height, or weight.

One of the limitations of this study is our inability to correct for varying degrees of intravesical prostatic protrusion as it affects the length of the urethral catheter taken up with urethral catheterization. Recruitment of only patients without prostatic enlargement or measurement of urethral length with a flexible cystoscope are options to overcome this limitation.