Hypospadias

Basics

DESCRIPTION

Hypospadias is one of the most common congenital anomalies of the male external genitalia. It is characterized by a urethral meatus that opens proximally on the ventral surface of the penis, scrotum, or the perineum. Classification is based on the position of the meatus relative to the penile shaft or surrounding structures (distal, middle, proximal). Although the ventral foreskin is incomplete in the vast majority of cases, the megameatus variant is characterized by an intact foreskin.

EPIDEMIOLOGY

  • 1/200 to 1/300 live male births
  • Concordance rates among twins: 18–77%
  • Megameatus variant: 5% of cases
  • Incidence is likely not increasing over time. Although there have been some data suggesting an increasing incidence over time, the majority of published studies in the U.S. population indicate a stable incidence.

RISK-FACTORS

  • In vitro fertilization
  • Maternal exposures to substances such as pesticides, hormones, phthalates, and phytoestrogens that can act as endocrine disruptors during penile development
  • Associated with maternal preexisting diabetes mellitus, placental insufficiency, and low birth weight
  • More common among Caucasians

GENETICS

  • Likely polygenic
  • Familial clustering: 7% of affected boys have an affected 1st- or 2nd-degree relative.
  • Equally maternally and paternally transmitted
  • Associated with genetic mutations in several genes involved in the androgen pathway and external genitalia development, including homeobox, fibroblast growth factor, and sonic hedgehog genes

ETIOLOGY

  • Due to incomplete fusion of the urethral folds during penile development, which is an androgen-driven process that occurs during weeks 8 to 16 of gestation
  • Likely multifactorial with environmental and genetic interplay
  • Defects in urethral development are usually accompanied by foreskin developmental defects (an incomplete ventral foreskin and dorsal hooded foreskin), except in the megameatus variant

ASSOCIATED-CONDITIONS

  • Usually idiopathic and isolated
  • Less commonly associated with certain chromosomal abnormalities and ~200 syndromes, including disorders of sexual differentiation (DSD)
  • Hypospadias, particularly proximal hypospadias, can be associated with an increased risk of other genitourinary (GU) malformations.
  • The most commonly associated GU malformations include the following:
    • Chordee
    • Cryptorchidism
    • Inguinal hernia

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