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DIFFERENTIATION OF THE UROGENITAL SINUS
Saturday, August 16, 2008
Until differentiation of the genital ducts begins, the urogenital sinus appears similar in both sexes during the middle and late embryonic period. For purposes of describing the origin of sinusal derivatives, the sinus can be divided into 3 parts: (1) the vesical part, or the large dilated segment superior to the entrance of the mesonephric ducts; (2) the pelvic part, or the narrowed tubular segment between the level of the mesonephric ducts and the inferior segment; and (3) the phallic part, often referred to as the definitive urogenital sinus (the anteroposteriorly elongated, transversely flattened inferiormost segment) (Fig 4–12). The urogenital membrane temporarily closes the inferior limit of the phallic part. The superior limit of the vesical part becomes delimited by conversion of the once tubular allantois to a thick fibrous cord, the urachus, by about 12 weeks. After differentiation of the vesical part of the sinus to form the epithelium of the urinary bladder, the urachus maintains its continuity between the apex of the bladder and the umbilical cord and is identified postnatally as the median umbilical ligament. Various anomalies of urachal formation can present as urachal fistula, cyst, or sinus, depending on the degree of patency that persists during obliteration of the allantois.
In both sexes, the caudal segments of each mesonephric duct between the urogenital sinus and the level of the ureter of the differentiating metanephric diverticulum (or ureteric bud) become incorporated into the posterocaudal wall of the vesical part (ie, urinary bladder) of the sinus (Fig 4–9 and Fig 4–10). As the dorsal wall of the bladder grows and “absorbs” these caudal segments, the ureters are gradually “drawn” closer to the bladder and eventually open directly and separately into it, dorsolateral to the mesonephric ducts (Fig 4–10 and Fig 4–11). The mesodermal segment of mesonephric duct incorporated into the bladder defines the epithelium of the trigone of the bladder, although this mesodermal epithelium is secondarily replaced by the endodermal epithelium of the sinusal bladder. After formation of the trigone, the remainder of each mesonephric duct (ie, the portion that was cranial to the metanephric diverticulum) is joined to the superior end of the pelvic part of the urogenital sinus. Thereafter, the ducts either degenerate (in females) or undergo differentiation (in males), as already discussed.
The urogenital sinus gives rise to the endodermal epithelium of the urinary bladder, the prostatic and membranous urethra, and most of the spongy (penile) urethra (except the glandular urethra). Outgrowths from its derivatives produce epithelial parts of the prostate and bulbourethral glands (Fig 4–17). The prostatic urethra receives the ejaculatory ducts (derived from the mesonephric ducts) and arises from 2 parts of the urogenital sinus. The portion of this urethral segment superior to the ejaculatory ducts originates from the inferiormost area of the vesical part of the sinus. The lower portion of the prostatic urethra is derived from the pelvic part of the sinus near the entrance of the ducts and including the region of the sinusal tubercle—the latter apparently forming the seminal colliculus. Early in the 12th week, endodermal outgrowths of the prostatic urethra form the prostatic anlage, the prostatic buds, from which the glandular epithelium of the prostate will arise. Differentiation of splanchnic mesoderm contributes other components to the gland (smooth muscle and connective tissue), as is the case also for mesodermal parts of the urinary bladder. The pelvic part of the sinus also gives rise to the epithelium of the membranous urethra, which later yields endodermal buds for the bulbourethral glands. The phallic, or inferior, part of the urogenital sinus proliferates anteriorly as the external genitalia form (during weeks 9–12) and results in incorporation of this phallic part as the endodermal epithelium of the spongy (penile) urethra (the distal glandular urethra is derived from ectoderm; see below).
Female: Urinary Bladder, Urethra, and Vagina
A. DEVELOPMENT
Differentiation of the female sinus is schematically presented in Fig 4–18 and illustrated in Fig 4–12 and Fig 4–19, Fig 4–20 and Fig 4–21. In contrast to sinusal differentiation in the male, the vesical part of the female urogenital sinus forms the epithelium of the urinary bladder and entire urethra. Derivatives of the pelvic part of the sinus include the epithelium of the vagina, the greater vestibular glands, and the hymen. Controversy exists about how the vagina is formed, mainly because of a lack of consensus about the origin and degree of inclusion of its precursory tissues (mesodermal paramesonephric duct, endodermal urogenital sinus, or even mesonephric duct). The most common theory is that 2 endodermal outgrowths, the sinovaginal bulbs, of the dorsal wall of the pelvic part of the urogenital sinus form bilateral to and join with the caudal tip of the uterovaginal primordium (fused paramesonephric ducts) in the area of the sinusal tubercle (Fig 4–19). This cellular mass at the end of the primordium occludes the inferior aspect of the canal, creating an endodermal vaginal plate within the mesodermal wall of the uterovaginal primordium. Eventually, the vaginal segment grows, approaching the vestibule of the vagina. The process of growth has been described either as “down-growth” of the vaginal segment away from the uterine canal and along the urogenital sinus or, more commonly, as “up-growth” of the segment away from the sinus and toward the uterovaginal canal. In either case, the vaginal segment is extended between the paramesonephric-derived cervix and the sinus-derived vestibule (Fig 4–19, Fig 4–20 and Fig 4–21). Near the fifth month, the breakdown of cells centrally in the vaginal plate creates the vaginal lumen, which is delimited peripherally by the remaining cells of the plate as the epithelial lining of the vagina. The solid vaginal fornices become hollow soon after canalization of the vaginal lumen is complete. The upper one-third to four-fifths of the vaginal epithelium has been proposed to arise from the uterovaginal primordium, while the lower two-thirds to one-fifth has been proposed as a contribution from the sinovaginal bulbs.
The fibromuscular wall of the vagina is derived from the uterovaginal primordium. The cavities of the vagina and urogenital sinus are temporarily separated by the thin hymen, which is probably a mixture of tissue derived from the vaginal plate and the remains of the sinusal tubercle. With concurrent differentiation of female external genitalia, inferior closure of the sinus does not occur during the 12th week of development, as it does in the male. Instead, the remainder of the pelvic part and all of the inferior phallic part of the urogenital sinus expand to form the vestibule of the vagina. Presumably, the junctional zone of pigmentation on the labia minora represents the distinction between endodermal derivation from the urogenital sinus (medially) and ectodermal skin (laterally).
B. ANOMALIES OF THE VAGINA
The vagina is derived from interaction between the uterovaginal primordium and the pelvic part of the urogenital sinus (Fig 4–18; see previous section above). The causes of vaginal anomalies are difficult to assess because integration of the uterovaginal primordium and the urogenital sinus in the normal differentiation of the vagina remains a controversial subject. Furthermore, an accurate breakdown of causes of certain anomalous vaginal presentations, as with many anomalies of the external genitalia, would have to include potential moderating factors of endocrine and genetic origin as well.
The incidence of absence of the vagina due to suspected vaginal agenesis is about 0.025%. Agenesis may be due to failure of the uterovaginal primordium to contact the urogenital sinus. The uterus is usually absent (Fig 4–22). Ovarian agenesis is not usually associated with vaginal agenesis. The presence of greater vestibular glands has been reported with presumed vaginal agenesis; their presence emphasizes the complexity of differentiation of the urogenital sinus.
Vaginal atresia, on the other hand, is considered when the lower portion of the vagina consists merely of fibrous tissue while the contiguous superior structures (the uterus, in particular) are well differentiated (perhaps because the primary defect is in the sinusal contribution to the vagina). In müllerian aplasia almost all of the vagina and most of the uterus are absent (Rokitansky-Küster-Hauser syndrome, with a rudimentary uterus of bilateral, solid muscular tissue, was considered virtually the same as this aplasia). Most women with absence of the vagina (and normal external genitalia) are considered to have müllerian aplasia rather than vaginal atresia.
Other somatic anomalies are sometimes associated with müllerian aplasia, suggesting multiple malformation syndrome. Associated vertebral anomalies are much more prevalent than middle ear anomalies, eg, müllerian aplasia associated with Klippel-Feil syndrome (fused cervical vertebrae) is more common than müllerian aplasia associated with Klippel-Feil syndrome plus middle ear anomalies (“conductive deafness”). Winter's syndrome, which is thought to be autosomal recessive, is evidenced by middle ear anomalies (somewhat similar to those in the triad above), renal agenesis or hypoplasia, and vaginal atresia (rather than aplasia of the paramesonephric ducts). Dysgenesis (partial absence) of the vagina and hypoplasia (reduced caliber of the lumen) have also been described.
Transverse vaginal septa (Fig 4–23) are probably not the result of vaginal atresia but rather of incomplete canalization of the vaginal plate or discrete fusion of sinusal and primordial (ductal) derivatives. Alternative explanations are likely since the histologic composition of septa is not consistent. A rare genetic linkage has been demonstrated. A single septum or multiple septa can be present, and the location may vary in upper or lower segments of the lumen. Longitudinal vaginal septa can also occur. A variety of explanations have been advanced, including true duplication of vaginal primordial tissue, anomalous differentiation of the uterovaginal primordium, abnormal variation of the caudal fusion of the müllerian ducts, persistence of vaginal plate epithelium, and anomalous mesodermal proliferation. Septa may be imperforate or perforated. A transverse septum creates the potential for various occlusive manifestations (eg, hydrometrocolpos, hematometra, or hematocolpos, depending on the composition of the trapped fluid). (See Chapter 31.)
Abnormalities of the vagina are often associated with anomalies of the urinary system and the rectum because differentiation of the urogenital sinus is involved in formation of the bladder and urethra as well as the vagina and vestibule. Furthermore, if partitioning of the cloaca into the sinus and anorectal canal is faulty, then associated rectal defects can occur. Compound anomalies may affect the urinary tract or rectum. The urethra may open into the vaginal wall; even a single vesicovaginal cavity has been described. On the other hand, the vagina can open into a persistent urogenital sinus, as in certain forms of female pseudohermaphroditism. Associated rectal abnormalities include vaginorectal fistula, vulvovaginal anus, rectosigmoidal fistula, and vaginosigmoidal cloaca in the absence of the rectum (see also Cloacal Dysgenesis, below).
C. ANOMALIES OF THE HYMEN
The hymen is probably a mixture of tissue derived from remains of the sinusal tubercle and the vaginal plate. Usually, the hymen is patent, or perforate, by puberty, although an imperforate hymen is not rare. The imperforate condition can be a congenital error of lack of central degeneration or a result of inflammatory occlusion after perforation. Obstruction of menstrual flow at puberty may be the first sign (Fig 4–23).
D. CLOACAL DYSGENESIS (INCLUDING PERSISTENCE OF THE UROGENITAL SINUS)
Anomalous partitioning of the cloaca by the abnormal development of the urorectal septum is rare, at least based on reported cases in the literature. As anticipated from a developmental standpoint, the incidence of associated genitourinary anomalies is high. Five types of cloacal or anorectal malformations are summarized in Table 4–3.
Rectocloacal fistula with a persistent cloaca provides a common canal or outlet for the urinary, genital, and intestinal tracts. The distinction between a canal and an outlet is one of depth (deep versus very shallow, respectively) of the persistent lower portion of the cloaca and, thus, the length of the individual urethral and vaginal canals emptying into the cloaca. The inverse relationship between depth (or length) of the cloaca and length of the vaginal and urethral canals is probably a reflection of the time when arrest of formation of the urorectal septum occurs. Although the bladder, the vagina, and the rectum can empty into a common cloaca as just described, other unusual variations of persistent cloaca can also occur.
For example, the vagina and rectum develop, but the urinary bladder does not develop as a separate entity from the cloaca. Instead, the vagina and rectum open separately into a “urinary bladder,” which has ureters entering posterolaterally to the vagina (vaginal orifice is in the “anatomic trigone” of the bladder-like structure). The external orifice from the base of this cloacal “bladder” is a single narrow canal. One explanation for this variant might be that arrest of formation of the urorectal septum occurs much earlier than does the separate development of distal portions of the 3 tracts (urethra, vagina, and anorectum) to a more advanced (but still incomplete) stage before urorectal septal formation ceases. The anomaly is probably rare.
With a rectovaginal fistula, the vestibule may appear anatomically normal but the anus does not appear in the perineum. The defect probably results from anorectal agenesis due to incomplete subdivision of the cloaca (similar agenesis in the male could result in a rectourethral fistula). The development of the anterior aspect of the vagina completes the separation of the urethra from the vagina, so there is not a persistent urogenital sinus. Anorectal agenesis is reputedly the most common type of anorectal malformation, and usually a fistula occurs. Rectovaginal, anovestibular (or rectovestibular; Table 4–3), and anoperineal fistulas account for most anorectal malformations.
In the absence of the anorectal defect (normal anal presentation) but presence of a persistent urogenital sinus with a single external orifice, various irregularities of the urethra and genitalia can appear. The relative positions of urethral and vaginal orifices in the sinus can even change as the child grows. In the discussion of anomalies of the labia majora (see following text), note is made of the association of a persistent urogenital sinus in female pseudohermaphroditism due to congenital adrenal hyperplasia. The vagina opens into the persisting pelvic part of the sinus, which extends with the phallic part of the sinus to the external surface at the urogenital opening. The sinus can be deep and narrow in the neonate, approximating the size of a urethra, or it can be relatively shallow.
Urinary tract disorders associated with persistent urogenital sinus include duplication of the ureters, unilateral ureteral and renal agenesis or atresia, and lack of or abnormal ascent of the kidneys. Variations in the anomalies of derivatives of the urogenital sinus appear to be related in part to the time of arrest of normal differentiation and development of the urogenital sinus, as well as to the impact of other factors associated with abnormal sexual differentiation, such as the variable degrees of response to adrenal androgen in congenital adrenal hyperplasia.
In both sexes, the caudal segments of each mesonephric duct between the urogenital sinus and the level of the ureter of the differentiating metanephric diverticulum (or ureteric bud) become incorporated into the posterocaudal wall of the vesical part (ie, urinary bladder) of the sinus (Fig 4–9 and Fig 4–10). As the dorsal wall of the bladder grows and “absorbs” these caudal segments, the ureters are gradually “drawn” closer to the bladder and eventually open directly and separately into it, dorsolateral to the mesonephric ducts (Fig 4–10 and Fig 4–11). The mesodermal segment of mesonephric duct incorporated into the bladder defines the epithelium of the trigone of the bladder, although this mesodermal epithelium is secondarily replaced by the endodermal epithelium of the sinusal bladder. After formation of the trigone, the remainder of each mesonephric duct (ie, the portion that was cranial to the metanephric diverticulum) is joined to the superior end of the pelvic part of the urogenital sinus. Thereafter, the ducts either degenerate (in females) or undergo differentiation (in males), as already discussed.
The urogenital sinus gives rise to the endodermal epithelium of the urinary bladder, the prostatic and membranous urethra, and most of the spongy (penile) urethra (except the glandular urethra). Outgrowths from its derivatives produce epithelial parts of the prostate and bulbourethral glands (Fig 4–17). The prostatic urethra receives the ejaculatory ducts (derived from the mesonephric ducts) and arises from 2 parts of the urogenital sinus. The portion of this urethral segment superior to the ejaculatory ducts originates from the inferiormost area of the vesical part of the sinus. The lower portion of the prostatic urethra is derived from the pelvic part of the sinus near the entrance of the ducts and including the region of the sinusal tubercle—the latter apparently forming the seminal colliculus. Early in the 12th week, endodermal outgrowths of the prostatic urethra form the prostatic anlage, the prostatic buds, from which the glandular epithelium of the prostate will arise. Differentiation of splanchnic mesoderm contributes other components to the gland (smooth muscle and connective tissue), as is the case also for mesodermal parts of the urinary bladder. The pelvic part of the sinus also gives rise to the epithelium of the membranous urethra, which later yields endodermal buds for the bulbourethral glands. The phallic, or inferior, part of the urogenital sinus proliferates anteriorly as the external genitalia form (during weeks 9–12) and results in incorporation of this phallic part as the endodermal epithelium of the spongy (penile) urethra (the distal glandular urethra is derived from ectoderm; see below).
Female: Urinary Bladder, Urethra, and Vagina
A. DEVELOPMENT
Differentiation of the female sinus is schematically presented in Fig 4–18 and illustrated in Fig 4–12 and Fig 4–19, Fig 4–20 and Fig 4–21. In contrast to sinusal differentiation in the male, the vesical part of the female urogenital sinus forms the epithelium of the urinary bladder and entire urethra. Derivatives of the pelvic part of the sinus include the epithelium of the vagina, the greater vestibular glands, and the hymen. Controversy exists about how the vagina is formed, mainly because of a lack of consensus about the origin and degree of inclusion of its precursory tissues (mesodermal paramesonephric duct, endodermal urogenital sinus, or even mesonephric duct). The most common theory is that 2 endodermal outgrowths, the sinovaginal bulbs, of the dorsal wall of the pelvic part of the urogenital sinus form bilateral to and join with the caudal tip of the uterovaginal primordium (fused paramesonephric ducts) in the area of the sinusal tubercle (Fig 4–19). This cellular mass at the end of the primordium occludes the inferior aspect of the canal, creating an endodermal vaginal plate within the mesodermal wall of the uterovaginal primordium. Eventually, the vaginal segment grows, approaching the vestibule of the vagina. The process of growth has been described either as “down-growth” of the vaginal segment away from the uterine canal and along the urogenital sinus or, more commonly, as “up-growth” of the segment away from the sinus and toward the uterovaginal canal. In either case, the vaginal segment is extended between the paramesonephric-derived cervix and the sinus-derived vestibule (Fig 4–19, Fig 4–20 and Fig 4–21). Near the fifth month, the breakdown of cells centrally in the vaginal plate creates the vaginal lumen, which is delimited peripherally by the remaining cells of the plate as the epithelial lining of the vagina. The solid vaginal fornices become hollow soon after canalization of the vaginal lumen is complete. The upper one-third to four-fifths of the vaginal epithelium has been proposed to arise from the uterovaginal primordium, while the lower two-thirds to one-fifth has been proposed as a contribution from the sinovaginal bulbs.
The fibromuscular wall of the vagina is derived from the uterovaginal primordium. The cavities of the vagina and urogenital sinus are temporarily separated by the thin hymen, which is probably a mixture of tissue derived from the vaginal plate and the remains of the sinusal tubercle. With concurrent differentiation of female external genitalia, inferior closure of the sinus does not occur during the 12th week of development, as it does in the male. Instead, the remainder of the pelvic part and all of the inferior phallic part of the urogenital sinus expand to form the vestibule of the vagina. Presumably, the junctional zone of pigmentation on the labia minora represents the distinction between endodermal derivation from the urogenital sinus (medially) and ectodermal skin (laterally).
B. ANOMALIES OF THE VAGINA
The vagina is derived from interaction between the uterovaginal primordium and the pelvic part of the urogenital sinus (Fig 4–18; see previous section above). The causes of vaginal anomalies are difficult to assess because integration of the uterovaginal primordium and the urogenital sinus in the normal differentiation of the vagina remains a controversial subject. Furthermore, an accurate breakdown of causes of certain anomalous vaginal presentations, as with many anomalies of the external genitalia, would have to include potential moderating factors of endocrine and genetic origin as well.
The incidence of absence of the vagina due to suspected vaginal agenesis is about 0.025%. Agenesis may be due to failure of the uterovaginal primordium to contact the urogenital sinus. The uterus is usually absent (Fig 4–22). Ovarian agenesis is not usually associated with vaginal agenesis. The presence of greater vestibular glands has been reported with presumed vaginal agenesis; their presence emphasizes the complexity of differentiation of the urogenital sinus.
Vaginal atresia, on the other hand, is considered when the lower portion of the vagina consists merely of fibrous tissue while the contiguous superior structures (the uterus, in particular) are well differentiated (perhaps because the primary defect is in the sinusal contribution to the vagina). In müllerian aplasia almost all of the vagina and most of the uterus are absent (Rokitansky-Küster-Hauser syndrome, with a rudimentary uterus of bilateral, solid muscular tissue, was considered virtually the same as this aplasia). Most women with absence of the vagina (and normal external genitalia) are considered to have müllerian aplasia rather than vaginal atresia.
Other somatic anomalies are sometimes associated with müllerian aplasia, suggesting multiple malformation syndrome. Associated vertebral anomalies are much more prevalent than middle ear anomalies, eg, müllerian aplasia associated with Klippel-Feil syndrome (fused cervical vertebrae) is more common than müllerian aplasia associated with Klippel-Feil syndrome plus middle ear anomalies (“conductive deafness”). Winter's syndrome, which is thought to be autosomal recessive, is evidenced by middle ear anomalies (somewhat similar to those in the triad above), renal agenesis or hypoplasia, and vaginal atresia (rather than aplasia of the paramesonephric ducts). Dysgenesis (partial absence) of the vagina and hypoplasia (reduced caliber of the lumen) have also been described.
Transverse vaginal septa (Fig 4–23) are probably not the result of vaginal atresia but rather of incomplete canalization of the vaginal plate or discrete fusion of sinusal and primordial (ductal) derivatives. Alternative explanations are likely since the histologic composition of septa is not consistent. A rare genetic linkage has been demonstrated. A single septum or multiple septa can be present, and the location may vary in upper or lower segments of the lumen. Longitudinal vaginal septa can also occur. A variety of explanations have been advanced, including true duplication of vaginal primordial tissue, anomalous differentiation of the uterovaginal primordium, abnormal variation of the caudal fusion of the müllerian ducts, persistence of vaginal plate epithelium, and anomalous mesodermal proliferation. Septa may be imperforate or perforated. A transverse septum creates the potential for various occlusive manifestations (eg, hydrometrocolpos, hematometra, or hematocolpos, depending on the composition of the trapped fluid). (See Chapter 31.)
Abnormalities of the vagina are often associated with anomalies of the urinary system and the rectum because differentiation of the urogenital sinus is involved in formation of the bladder and urethra as well as the vagina and vestibule. Furthermore, if partitioning of the cloaca into the sinus and anorectal canal is faulty, then associated rectal defects can occur. Compound anomalies may affect the urinary tract or rectum. The urethra may open into the vaginal wall; even a single vesicovaginal cavity has been described. On the other hand, the vagina can open into a persistent urogenital sinus, as in certain forms of female pseudohermaphroditism. Associated rectal abnormalities include vaginorectal fistula, vulvovaginal anus, rectosigmoidal fistula, and vaginosigmoidal cloaca in the absence of the rectum (see also Cloacal Dysgenesis, below).
C. ANOMALIES OF THE HYMEN
The hymen is probably a mixture of tissue derived from remains of the sinusal tubercle and the vaginal plate. Usually, the hymen is patent, or perforate, by puberty, although an imperforate hymen is not rare. The imperforate condition can be a congenital error of lack of central degeneration or a result of inflammatory occlusion after perforation. Obstruction of menstrual flow at puberty may be the first sign (Fig 4–23).
D. CLOACAL DYSGENESIS (INCLUDING PERSISTENCE OF THE UROGENITAL SINUS)
Anomalous partitioning of the cloaca by the abnormal development of the urorectal septum is rare, at least based on reported cases in the literature. As anticipated from a developmental standpoint, the incidence of associated genitourinary anomalies is high. Five types of cloacal or anorectal malformations are summarized in Table 4–3.
Rectocloacal fistula with a persistent cloaca provides a common canal or outlet for the urinary, genital, and intestinal tracts. The distinction between a canal and an outlet is one of depth (deep versus very shallow, respectively) of the persistent lower portion of the cloaca and, thus, the length of the individual urethral and vaginal canals emptying into the cloaca. The inverse relationship between depth (or length) of the cloaca and length of the vaginal and urethral canals is probably a reflection of the time when arrest of formation of the urorectal septum occurs. Although the bladder, the vagina, and the rectum can empty into a common cloaca as just described, other unusual variations of persistent cloaca can also occur.
For example, the vagina and rectum develop, but the urinary bladder does not develop as a separate entity from the cloaca. Instead, the vagina and rectum open separately into a “urinary bladder,” which has ureters entering posterolaterally to the vagina (vaginal orifice is in the “anatomic trigone” of the bladder-like structure). The external orifice from the base of this cloacal “bladder” is a single narrow canal. One explanation for this variant might be that arrest of formation of the urorectal septum occurs much earlier than does the separate development of distal portions of the 3 tracts (urethra, vagina, and anorectum) to a more advanced (but still incomplete) stage before urorectal septal formation ceases. The anomaly is probably rare.
With a rectovaginal fistula, the vestibule may appear anatomically normal but the anus does not appear in the perineum. The defect probably results from anorectal agenesis due to incomplete subdivision of the cloaca (similar agenesis in the male could result in a rectourethral fistula). The development of the anterior aspect of the vagina completes the separation of the urethra from the vagina, so there is not a persistent urogenital sinus. Anorectal agenesis is reputedly the most common type of anorectal malformation, and usually a fistula occurs. Rectovaginal, anovestibular (or rectovestibular; Table 4–3), and anoperineal fistulas account for most anorectal malformations.
In the absence of the anorectal defect (normal anal presentation) but presence of a persistent urogenital sinus with a single external orifice, various irregularities of the urethra and genitalia can appear. The relative positions of urethral and vaginal orifices in the sinus can even change as the child grows. In the discussion of anomalies of the labia majora (see following text), note is made of the association of a persistent urogenital sinus in female pseudohermaphroditism due to congenital adrenal hyperplasia. The vagina opens into the persisting pelvic part of the sinus, which extends with the phallic part of the sinus to the external surface at the urogenital opening. The sinus can be deep and narrow in the neonate, approximating the size of a urethra, or it can be relatively shallow.
Urinary tract disorders associated with persistent urogenital sinus include duplication of the ureters, unilateral ureteral and renal agenesis or atresia, and lack of or abnormal ascent of the kidneys. Variations in the anomalies of derivatives of the urogenital sinus appear to be related in part to the time of arrest of normal differentiation and development of the urogenital sinus, as well as to the impact of other factors associated with abnormal sexual differentiation, such as the variable degrees of response to adrenal androgen in congenital adrenal hyperplasia.
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