CONGENITAL ANOMALIES
The müllerian ducts first appear between the seventh and eighth weeks of embryonic life as invaginations of the coelomic epithelium overlying the genital folds. These ducts migrate caudally in the developing embryo, cross toward the midline, and fuse to form the anlage of the uterus, cervix, and upper three-quarters of the vagina. The unfused, cranial portions of the müllerian ducts develop into the fallopian tubes. The caudal fused column of cells moves further downward to join the urogenital sinus, which pushes in from the perineal surface. With the sloughing of the internal core of the cell column to form the vagina, the process is completed in 5 to 6 weeks, although full differentiation takes several weeks longer.
The majority of congenital anomalies of the uterus and vagina are caused
by a failure of the müllerian ducts to fuse completely or to develop after
fusion. The most extreme anomaly results from complete lack of union of the
ducts as a result of inhibition in growth at a very early stage. (The HOX genes
have been shown to play key roles in body patterning and organogenesis, and in
particular during genital tract development.) The result of this failure of
fusion in the adult is the complete absence of the uterus and vagina, but with
a normal ovary (because it is derived from a different embryonic source). The
fallopian tube may be well developed or rudimentary. The tube is connected near
the midline to a small bulb of fibrous tissue attached anteriorly to the bladder
peritoneum and posteriorly to the peritoneum of the rectosigmoid. This bulb,
which has its counterpart on the opposite side, represents the abortive attempt
to form a uterus and may occasionally contain an endometrial lining. Because
the vagina is absent, drainage of menstrual flow is impossible, and blood is
retained within the genital tract or must drain into the peritoneal cavity. The
external genitalia and the vaginal vestibule are normally developed,
distinguishing this condition from pseudohermaphroditism. Vaginal atresia is often
unrecognized until the occurrence of amenorrhea after puberty or dyspareunia
after marriage. Above the vestibular dimple, between bladder and rectum, a
potential space filled with loose areolar connective tissue may be found, which
can be opened surgically. The term Mayer-Rokitansky-Küster-Hauser syndrome is
sometimes applied to these cases of vaginal atresia, usually with absent cervix
and uterus.
A less extreme degree of failure in müllerian fusion leads to a double
vagina. In such instances the ducts have fused incompletely and have progressed
independently to maturity. In the perineal view, the longitudinal septum
dividing the vaginal compartments extends outward from the vestibule separating
the two cervices. A longitudinal section through the vagina shows the
appearance of the same anomaly from above, each uterus having its own fallopian
tube and ovary, and each theoretically fertile. The partial septate vagina is a milder degree of congenital malformation, which is caused by a failure of
the core of solid müllerian epithelium to slough completely at its lowermost
portion. The frequent occurrence of vaginal anomalies with other congenital
malformations in the genitourinary tract results from their common embryonic
heritage. The possibility of
associated lesions in the upper urinary tracts should always be investigated.
Incomplete canalization of the müllerian tubercle and sinovaginal bulb
can result in a transverse vaginal septum. These patients will have a
normal-appearing introitus leading to a foreshortened blind vaginal pouch.
After puberty, a large hematocolpos or hematometrium may result from this
outflow obstruction. Partial septa have been reported in women exposed in utero to diethylstilbestrol (DES).
