Development and growth of cavernosal sinusoidal endothelia in the external genitalia of human fetuses

Background: There is little information about when and how cavernosal sinusoidal endothelia develop in the external genitalia of fetuses.

Methods: We examined histological sections of erectile tissue in 37 human fetuses (25 males and 12 females) whose gestational age (GA) ranged from 8 to 40 weeks.

Results: The sinusoidal lumen was filled with blood in the glans of the penis and clitoris at a GA of 10 to 11 weeks, and in the corpus spongiosum at a GA of 15 to 16 weeks. The opening of the sinusoids with blood was much delayed in the corpus cavernosum of both sexes. The cross-reactivity of the endothelia with smooth muscle actin (SMA) antibody in the corpus spongiosum penis suggested that the development and growth of endothelia started at a site near the urethra and advanced to more distant site. In the corpus cavernosum, the opening of the lumen tended to occur near the midline septum at a GA of 20 weeks or later. After a GA of 25 weeks, the sinusoidal lumen fused, leading to long or large sinusoids. Simultaneously, the capsule became thick and the smooth muscle-rich midline septum had abundant protrusions that expanded anteriorly. Smooth muscles were rarely evident in interstitial tissues, even at late-term. In contrast, the initial female vestibular bulb corresponded to a belt-like cluster of SMA-positive rosette-like structures that appeared at a GA of 14 weeks.

Conclusion: Fusion between sinusoidal lumens with reconstruction of endothelia may occur as a consequence of shearing stress due to blood flow.