The hymenal membrane separates the vaginal lumen from the
urogenital sinus. Secondary to degeneration of the central epithelial cells, the hymen typically ruptures, leaving a thin fold of mucous membrane around the vaginal introitus.
An elective Caesarean section was performed and the newborn was treated early, the surgical act consisting of an excision of the cystic accessory phallic urethra with
urogenital sinus septation and vaginoplasty.
These two cases, similar to the present cases, exhibited a severe phenotype with clitoromegaly, labial fusion, and/or single
urogenital sinus at birth.
The formation of a
urogenital sinus in these animals occurs due absence of an external vaginal ostium (Yalcinkaya et al., 1993; Browne et al., 2006; Glickman et al., 2006).
The complexity of the folds increases towards the
urogenital sinus with the formation of branched villi whose epithelium flattens (Fig.
Affected females are born with enlarged clitoris, fused labioscrotal folds and a
urogenital sinus which may become a phallic urethera.
The 18-day-old pig embryo has a well-defined genital tubercle (Figure 4-3), a swelling on the ventral surface between the umbilical cord and opening of the
urogenital sinus. This will eventually form the male or female external genitalia.
"Embryologically, the vulva, distal vagina, trigone, and urethra are all derived from the
urogenital sinus and contain the highest concentration of estrogen receptors.
The Sonic hedgehog (Shh) gene is expressed in the epithelium of the male
urogenital sinus and is not regulated by testosterone.
The origin of SCEVs has been proposed to be from a possible embryonic remnant.[1] Although the embryologic development of the vagina is controversial, the hymenal ring appears to be derived from the
urogenital sinus.[1,17,18] The greatest controversy exists on the relative contributions of the mullerian ducts and
urogenital sinus to the development of the vagina.
The other two theories are that it is a mild anomaly of a midline abdominal wall closure defect, or that it is a congenital fistula of the primitive
urogenital sinus (3,4).
The cause of hypospadias is not known, it is presumed that affected foetus may secret inadequate quantities of testosterone or that there may be inadequate conversion of testosterone to dihydrotestosterone in target tissues of
urogenital sinus and external genitalia.
