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Anatomy > Embryology > Flashcards

Embryology Flashcards

1
Q

Incidence of ambiguous genitalia/disorders of sex development

A

1 in 4000

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2
Q

Causes of DSD

A

Either virilisation of a chromosomal XX female (46 XX DSD),
or undermasculinisation of a chromosomal XY (46 XY DSD)

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3
Q

Causes of female karyotype (46 XX DSD)

A
  • CAH (most common cause of DSD)
  • Exposure in utero to increased maternal circulating androgens (exogenous or endogenous), or placental aromatase deficiency (converts androgens, which are increased during pregnancy, to oestrogen)
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4
Q

Causes of male karyotype (46 XY DSD)

A

Disorders of androgen synthesis (e.g. 5-alpha reductase deficiency)
PAIS
Global defects in testicular function caused by mutations relating to gonadal development
- e.g. Swyer syndrome (partial gonadal dysgenesis)
PAIS (Partial androgen insensitivity syndrome)

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5
Q

CAH (cause, presentation, main issues)

A

21-hydroxylase deficiency
Presents in the newborn period with prenatal virilization without palpable gonads

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6
Q

45 X/46 XY mosaicism DSD

A
  • second most common category of DSD (after CAH 46,XX)
  • phenotype variable, most commonly hypospadias, descended (but infertile) testis on the R side and streak gonad on the left.
    = mixed gonadal dysgenesis
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7
Q

PAIS vs CAIS

A

Androgen insensitivity syndrome = androgen receptor or associated transcription factor gene mutations.
PAIS = (46,XY DSD) microphallus, or severe hypospadias and undescended testes
CAIS (46,XY) = typical female external genitalia, absent mullerian structures, high likelihood of a female gender identity

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8
Q

Management of DSD (principles)

A
  • Accurate diagnosis to guide rx and predict clinical and gender outcomes
  • Exclude life-threatening adrenal crisis in infants with salt-wasting CAH (newborn screening identifies most before this develops)
    – If not treated - vomiting, diarrhoea, hypotension and hypovolaemic shock can occur (typically day 10-20 of life)
  • Psychosocial - anxiety from parents, especially while awaiting dx.
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9
Q

DSD Evaluation - history

A

Fhx of conditions of DSD, e.g. CAH, PAIS, consanguinity
Maternal medications during pregnancy
- progestogens cause virilization and cypoterone causes undervirilization
- Virilization in the mother during pregnancy (e.g. unrx CAH, androgen producing tumour, placental aromatase deficiency).

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10
Q

Evaluation of DSD - examination

A
  • Size of phallus or clitoris (and presence of erectile tissue assessed on palpation)
  • Position of the urethral meatus (on phallus or perineum)
  • Presence of vaginal orifice
  • Presence of palpable gonads within the inguinal canal or genital folds
  • Fusion of the genital folds
  • Colour and rugosity of vaginal folds -> hyperpigmentation suggests CAH (incr production of melanocyte stimulating hormone). Rugosity suggests androgen exposure
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11
Q

5 Prader stages of DSD

A
  1. Isolated clitoromegaly
  2. Narrow vestibule with separate vaginal and urethral opening
  3. Single urogenital sinus/labia majora partially fused
  4. Micropenis
  5. Isolated crypto-orchidism (undescended testes)
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12
Q

Evaluation DSD - Investigations

A

FISH and full karyotype (XX or XY)
17 OHP (for CAH)
Urea and electrolytes
AMH
USS of pelvis
EUA with vaginoscopy and cystoscopy

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13
Q

DSD - management

A
  1. Rx salt wasting crisis (CAH are at risk of electrolyte imbalance and hypoglycemia)
  2. Gender assignment
    –> don’t assign a gender and hep parents to work through this
    –> once diagnosis found, discuss with the parents the gender the child will be raised under - usually based on anatomy and future reproductive and sexual potential
  3. Gonadectomy in those at risk of developing malignancy (esp if being raised female)
    –> dysgenic gonads (30% risk malignancy)
    –> PAIS
    –> defects in testosterone biosynthesis
  4. Feminizing genital surgery (timing is debate)
    –> Reduction of clitoral size (may result in alteration in sensation)
    –> Opening of the vaginal canal (allows passage of menstrual blood and intercourse)
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14
Q

CAH - inheritance, cause,

A
  1. Autosomal recessive
  2. Enzyme deficiency 21-hydroxylase in corticosteroid pathway (90% of cases)
    –> no production of cortisol or aldosterone (salt wasting)
    –> second most common deficiency is 11 beta-hydroxylase
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15
Q

CAH - pathophysiology

A
  • Reduced production of cortisol
  • ACTH is increased due to less negative feedback from cortisol
  • Increased ACT -> hypertrophy of adrenal glands
  • Increased levels of 17-OHP (hydroprogesterone) -> androgen synthesis
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16
Q

CAH - diagnosis

A

Raised 17-OHP
IF equivocal, synacthen test is done (= give ACTH, then cortisol and 17-OHP levels are measured)

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17
Q

CAH - presentation and management

A
  • If both cortisol and corticosterone are deficient then the baby is at risk of a salt wasting crisis
    -> needs immediate rx with hydrocortisone and fludrocortisone to prevent hyponatraemia, hypoglycaemia and hyperkalaemia
  • In female infant there can be varying degrees of virilization
    –> vagina can join the posterior wall of the urethra causing a low or high defect
  • In late onset CAH, virilization may occur at puberty and presentation is similar to PCOS
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18
Q

CAIS and PAIS - inheritance, karyotype

A

CAIS = more common than PAIS
X-linked inheritance in most cases
XY, testes present

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19
Q

CAIS pathophysiology

A
  • There is normal testicular function of androgens
  • Abnormal androgen receptors
  • Virilization of the external genitalia is incomplete or absent because it is dependent on androgen receptor activity
  • As the testes produce AMH, the mullein structures regress
  • The fallopian tubes, uterus and upper 2/3 of the vagina are absent
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20
Q

CAIS/PAIS presentation

A

CAIS - genitalia have a normal female appearance = the most common cause of primary amenorrhoea. Pubic and axillary hair are absent.
PAIS - varying degrees of virilization ranging from defects in spermatogenesis and isolated hypospadias at birth. The gonads are usually completely undescended. They may be located in the inguinal canal and first presentation may be of a phenotypically normal female with bilateral inguinal hernias. During puberty, some degree of virilization occurs in PAIS, but not in CAIS.

21
Q

CAIS/PAIS - diagnosis

A
  • FISH and karyotype (46,XY)
  • Normal rise in testosterone levels after HCG stimulation test (in the presence of ambiguous genitalia or female external genitalia
22
Q

CAIS/PAIS - Management

A
  1. Psychological support
  2. Gonadectomy and oestrogen replacement
    (in PAIS, gonadectomy should be done before puberty if the child is raised female otherwise virilization will occur)
  3. Explanation re no menstruation/ability to carry a pregnancy
  4. Vaginal dilation and sometimes surgery
23
Q

5 Alpha Reductase Deficiency - karyotype, risk factor

A

Rare and increases with consanguinity
46,XY

24
Q

5 Alpha Reductase Deficiency - pathophysiology

A
  • At least 5 types
  • All lack the enzyme that converts testosterone into DHT (needed for virilization of male external genitalia)
  • Genitalia may be ambiguous or female at birth
  • Virilization occurs during puberty
25
Q

5 Alpha Reductase Deficiency - Ix

A
  • HCG stimulation results in normal testosterone but decreased DHT
  • Can measure 5 alpha reductase levels in genital skin fibroblasts
26
Q

Management

A
  • Child raised as female, then gonadectomy should be performed before puberty to avoid virilization
  • In male phenotype, surgery may be needed to correct hypospadias
  • Psychosexual and genetic counselling
27
Q

Swyer syndrome (XY gonadal dysgenesis)

A
  • 46,XY
  • Defect in SRY gene on Y chromosome
  • Testes are not properly formed => no AMH or testosterone produced
    -> default is female external genitalia. The mullerian ducts are not suppressed and so go on and form a uterus and fallopian tubes.
  • Have streak nonfunctioning gonads in the abdomen
  • Generally not suspected until puberty when no secondary sex chx form and periods don’t start (no hormonal stimuli).
    –> sometimes have sparse pubic hair due to limited androgens from adrenals
28
Q

XY Gonadal dysgenesis (Swyer syndrome) - Management

A
  • Oestrogen and progesterone for secondary sexual development
  • Gonadectomy to reduce risk of malignancy
29
Q

MRKH syndrome (Mayer-Rokitansky-Kuster-Hauser)

A

XX gonadal/mullerian dysgenesis. 46,XX
Autosomal dominant with incomplete penetrance and variable expressivity.
= Defect in the formation of uterus, fallopian tubes and upper 1/3 of vagina from a defect in differentiation of the paramesonesphric or mullerian ducts.
Normally not detected until puberty and is a cause of primary amenorrhoea.
Girls will have secondary sexual chx as normal ovaries producing hormones

30
Q

MRKH1

A

(80%)
- only the structures developing from the mullerian duct are affected

30
Q

MRKH2

A

(20%)
- the structures developing from the mullerian duct are affected as well as malformations in other systems such as skeletal and renal

30
Q

MRKH - Investigations

A

Pelvic USS
Karyotype

30
Q

MRKH - Rx

A

Surgery to lengthen vagina.
Psychological support.
Fertility can be through a surrogate as have oocytes that can be collected.
Uterine transplantation.

31
Q

Congenital uterine and vaginal anomalies - incidence & cause

A

Incidence between 0.5-6%
Uterine anomalies are the result of abnormal development of the mullerian ducts during embryogenesis

31
Q

Congenital uterine and vaginal anomalies

A

Hx:
- Primary amenorrhoea with or without cyclical pain (obstructed menstruation)
–> imperforate hymen, transverse vaginal septum, vaginal or cervical agenesis, uterine agenesis
- Dysmenorrhoea (non communicating obstructed horn)
- Dyspareunia (vaginal septum)
- Sub fertility
- Recurrent miscarriages
- Obstetric complications (obstructed labour, malposition)
In most cases there are no sx or hx of note

32
Q

Congenital uterine and vaginal anomalies - examination

A
  • Shorted vagina, septum visualised
  • Bulky enlarged uterus
  • Absent cx or blind ended vagina
  • Double vagina and cervices
  • Imperforate hymen with a bluish bulge behind the
33
Q

Uterine and vaginal congenital anomalies

A
  • Pelvic and renal USS
  • HSG
  • MRI
  • Laparoscopy and hysteroscopy
34
Q

Imperforate hymen - management

A

Surgical excision and drainage

35
Q

Low transverse vaginal septum - management

A

Surgical excision

36
Q

Cervical agenesis - management

A

Perform an anastomosis between the vagina and the uterus so that blood can drain during menstruation (similar to trachelectomy)

37
Q

Non communicating rudimentary horn with functioning endometrium

A

-> cyclical pain
- Excision of the horn either laparoscopically or open
- Can give GnRH analogues pre-surgery to suppress symptoms and thin the endometrium

38
Q

Septate or subseptate uterus - management

A

Resect hysteroscopically if recurrent miscarriages/seeking fertility rx

39
Q

Bicornuate uterus - management

A

Can resect septum hysteroscopically if needed for fertility (generally not needed)

40
Q

Uterine didelphus associated with

A

50% associated with renal anomalies (usually missing R kidney)

41
Q

Vaginal agenesis (cause, management)

A
  • Occurs due to MKRH or AIS syndrome
  • Dilators can be used to lengthen and stretch vaginal tissue
  • Surgical procedures
42
Q

Sex determination (chromosomal, morphological)

A

At conception, when either an X or Y containing sperm fertilizes an ovum.
Morphological differentiation at week 7 when undifferentiated gonad becomes a testes or an ovary.

43
Q

Internal genitalia development

A

Week 5: thickening in the medial side of each mesonephros.
Week 6: primordial germ cells migrate from yolk sac to gonadal ridge. The paramesonephric ducts lie lateral to the mesonephric ducts and eventually become the internal female sex organs.
XX: gonad develops into an ovary (does not yet produce hormones). In the absence of testosterone and AMH, mesonephric ducts regress and paramesonephric ducts become the fallopian tubes, uterus and upper vagina.
- Cranial ends form the tubes, ducts then fuse caudally to eventually become uterus and upper vagina.
XY: SRY gene is responsible for differentiation of the gonad into a testes.
- Week 8: testes produce testosterone and AMH
- Testosterone drives formation of male genitalia
- AMH suppresses development of mullerian ducts

44
Q

External genitalia Embryology

A
  • Forms from the genital tubercle, urogenital folds and labioscrotal swelling
  • Undifferentiated until week 9
  • Default development is female
  • In the absence of a hormonal stimulus, the genital tubercle becomes the clitoris, labioscrotal folds form the labia majora and the urogenital sinus forms the vestibule and lower part of the vagina.
  • In the male embryo: external genitalia is virilized under the stimulation of DHT (potent derivative of testosterone) -> genital tubercle becomes penis, labioscrotal swellings fuse to form the scrotum. Urogenital folds fuse along ventral surface of penis to form urethra.
  • The fetus is identifiable as male or female by 12th week of gestation

Anatomy (2 decks)

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