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4.1 AMBIGUOUS GENITALIA

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EPIDEMIOLOGY/GENETICS

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Definition Ambiguous genitalia is a term used to describe the clinical situation when examination of the external genitalia does not allow a clear gender assignment. Those conditions where chromosomal sex and phenotypic sex do not correspond are called disorders of sexual development.

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Epidemiology The condition occurs in 1 in 5000 live births.

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Embryology The term ambiguous genitalia can be used for those disorders with abnormally formed genitalia (severe penile hypospadias) to complete sex reversal (Smith-Lemli-Opitz syndrome). The most common etiology of isolated ambiguous genitalia is congenital adrenal hyperplasia (CAH), with masculinization of the female fetus (90% of cases). Other congenital abnormalities are present in up to 40% of infants with genital malformations. Additional etiologies of ambiguous genitalia, especially with associated malformations, are chromosomal abnormalities (trisomies 13 and 18, and triploidy) and over 50 genetic syndromes/associations, including Smith-Lemli Opitz syndrome, velocardiofacial syndrome, Prader-Willi syndrome, VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, limb abnormalities) association, CHARGE (coloboma, heart defect, atresia choanae, retarded growth, genital anomaly, ear abnormality) association, Fraser syndrome, and Cornelia de Lange syndrome.

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Inheritance Patterns Congenital adrenal hyperplasia is autosomal recessive. Recurrence risks for other conditions are dependent on their specific inheritance patterns.

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Teratogens Isotretinoin is teratogenic.

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Prognosis Prognosis depends on the degree of genital malformation and the underlying etiology. The psychological and social implications of gender assignment in these infants require a multidisciplinary team approach.

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SONOGRAPHY

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FREQUENT FINDINGS
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  • Short phallus/clitoromegaly

  • Bifid scrotum/fused labia

  • Abnormal phallic shape

  • Undescended testes in the third trimester

  • Abnormal urinary stream

  • Associated congenital anomalies

    • Urogenital

    • Extragenital

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LESS FREQUENT
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  • Discrepancy between the external and internal fetal gender

    • Presence or absence of the uterus

      • The presence of a uterus results in an increased distance between the bladder and rectum.

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KEY FINDINGS/PITFALLS
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  • Uncertain appearance of external genitalia should prompt a more detailed assessment.

    • Clitoris versus penis

    • Labia versus scrotum

  • Late second- or third-trimester evaluation can look for testicular descent or the uterus.

    • Testicular descent is first noted at 25 weeks’ gestation.

      • Testicular descent occurs in 62% of cases between 28 and 30 weeks’ gestation; 93% of fetuses at 32 weeks’ gestation have descended testes.

        • Visualization of the testes distinguishes XY and XX disorders of sexual development.

      • The presence of a uterus results in an increased distance between the bladder and rectum compared to normal male fetuses.

        • The term uterus measures 32 ± 5 mm in length and 20 mm transversely.

  • Congenital adrenal hyperplasia

    • Hypertrophied adrenal glands

      • In the transverse plane, adrenals are enlarged and are circular rather than triangular.

      • They are first detected at 22 weeks’ gestation.

  • Hypospadias

    • Usually, hypospadias occurs (50%) on the distal penis (first degree).

    • With second-degree hypospadias (30%), the urethral opening is along the penile ...

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