Development of nerves and vessels in the penis during the human fetal period.

Introduction: Although nerves and vessels of the penis play important role in erection, there are few studies on their development in human fetus. Therefore, the objective of the present study is to analyze, quantitatively, in the corpora cavernosa and corpus spongiosum, the development of the nerves and vessels in the fetal penis at different gestational ages.

Material and methods: Fifty-six fresh, macroscopically normal human fetuses aged from 13 to 36 weeks post-conception (WPC) were used. Gestational age was determined by the foot length criterion. Penises were immediately fixed in 10% formalin, and routinely processed for paraffin embedding, after which tissue sections from the mid-shaft were obtained. We used immunohistochemical staining to analyze the nerves and vessels in the corpus cavernous and in the corpus spongiosum. These elements were identified and quantified as percentage by using the Image-J software.

Results: The quantitative analysis showed that the percentage of nerves varied from 3.03% to 20.35% in the corpora cavernosa and from 1.89% to 23.88% in the corpus spongiosum. The linear regression analysis indicated that nerves growth (incidence) in the corpora cavernosa and corpus spongiosum correlated significantly and positively with fetal age (r2=0.9421, p<0.0001) and (r2=0.9312, p<0.0001), respectively, during the whole fetal period studied. Also, the quantitative analysis showed that the percentage of vessels varies from 2.96% to 12.86% in the corpora cavernosa and from 3.62% to 14.85% in the corpus spongiosum. The linear regression analysis indicated that vessels growth (appearance) in the corpora cavernosa and corpus spongiosum correlated significantly and positively with fetal age (r2=0.8722, p<0.0001) and (r2=0.8218, p<0.0001), respectively, during the whole fetal period studied. In addition, the linear regression analysis demonstrated a more intense growth rate of nerves in the corpus spongiosum during the 2nd trimester of gestation, when compared with nerves in the corpora cavernosa. In addition, the linear regression analysis demonstrated a more intense growth rate of vessels in the corpus spongiosum when compared with the corpora cavernosa, during the whole fetal period studied.

Conclusions: In the fetal period, the human penis undergoes major developmental changes, notably in the content and distribution of nerves and vessels. We found strong correlation between nerves and vessels growth (amount) with fetal age, both in the corpora cavernosa and corpus spongiosum. There is significant greater proportional number of nerves than vessels during the whole fetal period studied. Also, nerves and vessels grow in a more intense rate than that of the corpora cavernosa and corpus spongiosum areas.