Editing External Genital Anomalies in Boys (section)

== Normal Male External Genitalia ==

* '''Embryology'''
** '''At 9-13 weeks of gestation, dihydrotestosterone (DHT) simulates androgen receptors the'''
**# '''Genital tubercle''' '''to differentiate into penis'''
**# '''Urethral folds to differentiate into the corpus spongiosum/penile shaft'''
**# '''Labioscrotal swellings to differentiate into scrotum'''
**#* '''Also known as genital swellings or labioscrotal folds'''§
**# '''The male develops in a proximal-to-distal manner'''
**# '''As the penis forms from the elongation and enlargement of the phallus, the lateral walls of the urethral groove form from the ventrally located urethral folds, which then fuse in the midline.'''
**# '''The scrotum forms from midline fusion of the labioscrotal swellings as delineated by the scrotal raphe.'''
** '''By the end of the first trimester (12 weeks), the external genitalia are completely masculinized'''
*** '''US sex determination after 13 weeks is accurate in 99-100%''' of cases of gestation without malformed external genitalia
** '''In females and males with abnormalities in testosterone and/or DHT production, 5α-reductase deficiency, or androgen-receptor insufficiency, the'''
**# '''Genital tubercle passively become the clitoris'''
**# '''Urethral folds passively become the''' '''labia minora'''
**# '''Labioscrotal swellings passively become the labia majora'''
* See Table 146-3: Tanner Classification of Sexual Maturity Stages in Boys