KEY NOTES CHAPTER 7: THE TRUNK AND UROGENITAL SYSTEM - Hypospadias. Flashcards
Apart from the 3 characteristic abnormalities, what other findings may be present?
∘ Flattened glans penis ∘ Downward glans tilt ∘ Deviation of the midline penile raphe ∘ Scrotal encroachment onto the penile shaft ∘ Midline scrotal cleft ∘ Penoscrotal transposition.
What is hypospadias?
A congenital condition characterised by:
- Abnormally proximal urethral meatus on the ventral aspect of the penis or scrotum.
- Hooded, ventrally deficient, prepuce (foreskin).
- Ventral curvature of the penis (chordee).
What is ‘Megameatus intact prepuce’ (MIP)?
MIP = variant of hypospadias.
∘ normal foreskin that conceals a glanular or distal shaft hypospadias.
What is the epidemiology of hypospadias?
- 1 in 300 live male births.
- Increased risk of hypospadias in:
∘ +ve FHx (4-10%)
∘ IVF
∘ Placental insufficiency - low birth weight, preterm, maternal obesity, diabetes, hypertension. - 10% associated with inguinal hernias.
- 20% of hypospadias associated with other GU abnormalities:
∘ cryptorchidism: 3% of distal, 10% proximal.
∘ asymptomatic paraurethral sinuses, urethral valves, enlarged prostatic utricle.
What is the aetiology?
• in most cases is unknown.
• Presuming hypospadias is a form of developmental arrest, these factors are implicated:
∘ Defects of testosterone synthesis
∘ Androgen receptor deficiency
∘ Mutations in FGF8 and FGFR2 genes
∘ Increased levels of exogenous (environmental) oestrogens.
How is hypospadias classified?
Duckett’s classification (position of urethral meatus).
Distal (85%) 1 Glanular 2 Subcoronal 3 Distal penile 4 Midshaft
Proximal 5 Proximal penile 6 Penoscrotal 7 Scrotal 8 Perineal.
How do the internal organs develop?
Internal organs
• Embryo is sexually indeterminate until week 6.
• 6th week: gonads arise from genital ridges and differentiate into their male and female forms, in response to arrival of primordial germ cells from yolk sac.
• Internal sex organs form from the mesonephric and paramesonephric ducts:
What does the mesonephric ducts form?
- Aka Wolffian duct.
- Forms majority of male internal sex organs.
• The sex-determining region of the Y chromosome (SRY) induces:
- genital ridge cells to
differentiate into Sertoli cells which secrete Müllerian-inhibiting factor which causes paramesonephric ducts to regress (8th-10th weeks).
- genital ridge mesenchyme to differentiate into Leydig cells which secrete testosterone and stimulates development of:
∘ Mesonephric ducts
∘ Genital tubercle.
• In males, mesonephric ducts give rise to 'SEED': ∘ Seminal vesicles ∘ Epididymis ∘ Ejaculatory ducts ∘ Ductus (vas) deferens.
(Paramesonephric ducts degenerate into appendix testis and prostatic
utricle).
What does the paramesonephric ducts form?
• Aka Müllerian duct.
• In females, paramesonephric ducts persist and develop into:
∘ Fallopian tubes
∘ Uterus
∘ Cervix
∘ Upper vagina.
- The lower vagina is initially occluded by the vaginal plate.
- This elongates during 3rd-5th months and subsequently canalises to form inferior vaginal lumen.
(Without Y chromosome and SRY, Sertoli cells, Müllerian-inhibiting factor, Leydig cells and androgen production are not formed and mesonephric ducts degenerate).
How do the external organs develop?
• Before 11th week, external genitalia are sexually indistinct.
• At 11th week, the external genitalia consist of:
∘ Central urethral groove (endoderm)
∘ Urethral folds either side of the urethral groove
∘ Labioscrotal swellings either side of the urethral folds
∘ Genital tubercle anteriorly.
• Male or female differentiation depends upon androgen receptor signalling.
How does the male external genitalia develop?
- Genital tubercle forms the penis.
- Urethral groove grows distally down genital tubercle (but not to tip of penis).
- Distal glanular urethra is formed by ectodermal ingrowth from the glans penis, evidenced by stratified squamous epithelium in fossa navicularis.
- Urethral folds fuse (proximal-to-distal) over urethral groove, forming a tubed urethra.
• Embryonic penis initially exhibits a ventral curvature.
∘ Chordee may therefore be due to arrest of penis development at this stage.
- Labioscrotal swellings fuse to form the scrotum.
- Testes descend into scrotum, with aid of the gubernaculum, around 7th month.
How does the female external genitalia develop?
• Genital tubercle forms the clitoris.
• Urethral groove does not extend into genital tubercle.
• Urethral folds do not fuse over urethral groove. Instead, they form:
∘ Labia minora
∘ Prepuce of the clitoris.
• Labioscrotal swellings become labia majora.
Describe the anatomy of the penis.
Root
Body
Glans
What does the root of the penis consist of?
- Bulb of the penis centrally.
- Continues as corpus spongiosum in the body.
- Penetrated by the spongy urethra and paired bulbourethral arteries. - Crura (each side of the bulb).
- Continues as corpus cavernosum in the body.
- Attached to ischiopubic rami.
- The deep arteries of the penis enter each crus to run in corpora cavernosa. - Bulbospongiosus and ischiocavernosus muscles.
What does the body of the penis consist of?
∘ Two adjacent corpora cavernosa (dorsal).
∘ Single corpus spongiosum (ventral), containing spongy urethra.
• These three cylinders of tissue are enclosed by tunica albuginea -> deep fascia of penis (Buck’s fascia)
∘ Paired dorsal arteries of the penis, a dorsal vein and dorsal nerves are contained within
Buck’s fascia.
• Subcutaneous connective tissue contains abundant smooth muscle fibres (dartos fascia - continuous with Colles’ fascia of perineum).
