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

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

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.

The sinusoidal lumen was filled with blood in the glans of the penis and clitoris at a GA of 10-11 weeks, and in the corpus spongiosum at a GA of 15-16 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.

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