Neuroanatomical ontogeny of the human fetal penis

Objective To determine the development of the human penis, and hence the cause of congenital anomalies, using an immunohistochemical analysis of fetal penile ontogeny. Materials and methods In 25 human fetal penile specimens (gestational age 8 to 23 weeks) various tissues were localized immunohistochemically using stains for alpha-actin (smooth muscle), cytokeratin 8 and 14 (epithelium) and protein gene-product (PGP) 9.5 (neurons). Results Nerves were identified in the penis with anti-PGP in specimens of all ages, prominent dorsally at the 11 and 1 o'clock positions but also extending around the tunica to the junction of the corpus spongiosum and corpora cavernosa, suggesting that these structures may be injured in procedures which straighten the penis. The nerves continued into the glans on the dorsal aspect, suggesting that glans reduction in feminizing genitoplasties should be performed on the ventral aspect. Smooth muscle was first noted at 10 weeks' gestation, with epithelial differentiation occurring in the earliest specimens studied (8 weeks' gestation). With time, smooth muscle density was highest in the corpus spongiosum, especially between it and the corpora cavernosa. Smooth muscle also developed close to the urethral epithelium. The tunica albuginea showed consistent variations in thickness, with the mid-dorsal 12 o'clock position being the thickest, followed by the 5 and 7 o'clock periurethral positions. Conclusion A better knowledge of penile development and of the relationship of the nerves to the corpora cavernosa is useful in the strategic design of penile straightening procedures and feminizing genitoplasties.