ARPKD: AR; PKHD1; presents in infants; Potter sequence if severe Extrarenal (ARPKD): Congenital hepatic fibrosis → portal HTN, splenomegaly
Hypospadias vs Epispadias
Embryologic defect in each, location of opening, and which is associated with bladder exstrophy?
Answer
Hypospadias (common): Urethral folds fail to fuse → opening on VENTRAL (inferior) surface → glanular > subcoronal > midshaft. Do NOT circumcise (foreskin used for repair). Epispadias (rare): Abnormal positioning of genital tubercle → opening on DORSAL (superior) surface. Associated with bladder exstrophy. Mnemonic: "Epi" = "E" on top; "Hypo" = below
Cryptorchidism
Path, timing of orchidopexy, and complications if untreated?
Answer
Path: Testes fail to descend through inguinal canal (guided by gubernaculum); processus vaginalis may persist → communicating hydrocele or hernia Treatment: Orchidopexy by 6 months (no later than 12 mo) If untreated: • Seminoma (↑ risk, even after surgery) • Infertility (heat-sensitive spermatogenesis) • Testicular torsion, inguinal hernia Labs: ↓ inhibin B + normal testosterone (Sertoli damage before Leydig)
21-Hydroxylase Deficiency
Classic triad, BP, electrolytes, screening marker, and treatment?
Embryology, why it's more common in females, and classic symptom pattern in girls?
Answer
Embryology: Incomplete absorption of mesonephric duct → ureteric bud implants too low (outside trigone) More common in ♀: mesonephric remnant drains into Müllerian derivatives (vagina/cervix/urethra); in ♂ it drains into Wolffian derivatives (vas, seminal vesicle) Classic ♀ symptom:Continuous dribbling/wetting PLUS normal voiding — because the ectopic ureter drains below the external urethral sphincter Assoc: Duplicated collecting system (upper-pole ureter is usually the ectopic one — Weigert-Meyer rule)
Posterior Urethral Valves
Who gets it, path, most common cause of bladder outlet obstruction, and diagnostic imaging?
Answer
Who: Boys only; most common cause of bladder outlet obstruction in male infants Path: Abnormal folds in prostatic urethra block urine outflow → bilateral hydroureter → hydronephrosis → renal damage; severe cases → oligohydramnios + Potter sequence Dx: Prenatal US (dilated bladder with "keyhole sign" + bilateral hydronephrosis) → VCUG confirms (voiding cystourethrogram) Tx: Endoscopic valve ablation
Gartner's Duct Cyst / Prostatic Utricle
What are these remnants, and which duct gives rise to each?
Answer
Gartner's duct cyst (♀):Wolffian duct remnant in the lateral vaginal wall or broad ligament — typically asymptomatic, occasionally dyspareunia or mass
Prostatic utricle (♂):Müllerian duct remnant in males; small midline blind pouch in the prostate (homolog of uterus/upper vagina). Usually asymptomatic; occasionally infected → utricular abscess
Also: Appendix testis = Müllerian remnant at upper pole of testis
Step 1-Style MCQs: Select the best answer for each question. Your choice locks in immediately and the explanation reveals automatically. Green = correct, Red = incorrect.
Question 1 of 6 — Potter Sequence
A 32-week male neonate is delivered by emergency C-section after a prenatal ultrasound at 22 weeks showed severe oligohydramnios and absence of visible kidneys. On exam he has flattened facial features, low-set ears, limb positioning deformities, and profound respiratory distress. He dies within 3 hours of birth despite aggressive ventilatory support. Which of the following best explains the immediate cause of death in this infant?
AAcute renal failure with uremia and hyperkalemia
BPulmonary hypoplasia from inadequate amniotic fluid during lung development
CCardiac tamponade from congenital cardiomyopathy
DIntracranial hemorrhage from coagulopathy
ERespiratory distress syndrome from surfactant deficiency
B — Pulmonary hypoplasia. The cause of death in Potter sequence is pulmonary hypoplasia, not renal failure. Fetal urine produces most of the amniotic fluid in the second trimester — without kidneys, oligohydramnios develops. Amniotic fluid is essential for lung canalization and alveolar expansion during weeks 16–26. Without it, the lungs fail to mature → immediate respiratory failure at birth. Mnemonic "POTTER" includes Pulmonary hypoplasia first because it's the lethal feature. Choice E (RDS) is a different surfactant-related issue seen in premature babies with normal lung development.
Question 2 of 6 — Horseshoe Kidney
A 14-year-old girl with short stature, webbed neck, a wide "shield" chest, and primary amenorrhea is found on abdominal imaging to have a horseshoe kidney. Her karyotype is 45,X. Which developmental event best explains the kidney malformation?
AFailure of the pronephros to regress at the end of week 4
BAbnormal ureteric bud bifurcation resulting in duplicate collecting systems
CMidline fusion of the metanephric blastemas followed by arrested ascent at the inferior mesenteric artery
DIncomplete absorption of the mesonephric duct into the urinary bladder
EPersistence of the urachus between the bladder dome and the umbilicus
C — Midline fusion blocked at the IMA. In a horseshoe kidney, the inferior poles of both metanephric blastemas fuse across the midline during initial kidney formation. As the kidneys ascend, the fused inferior portion catches on the IMA, fixing the kidney at approximately L3–L4. Horseshoe kidney is strongly associated with Turner syndrome (45,X) and is also seen in trisomy 18. Incomplete mesonephric duct absorption (D) causes ectopic ureter; urachal persistence (E) causes urachal fistula or cyst.
Question 3 of 6 — 21-Hydroxylase Deficiency
A 2-week-old phenotypically female infant presents with vomiting, poor feeding, and lethargy. Exam shows ambiguous genitalia with clitoromegaly and rugated labia. Labs: Na⁺ 124 mEq/L, K⁺ 6.8 mEq/L, glucose 48 mg/dL, BP 60/35 mmHg. Newborn screen shows markedly elevated 17-hydroxyprogesterone. What is the most appropriate immediate treatment?
ADexamethasone alone
BSpironolactone + potassium binder
CIV fluids + hydrocortisone + fludrocortisone
DLeuprolide + flutamide
ECorrective genitoplasty
C — IV fluids + hydrocortisone + fludrocortisone. This is classic 21-hydroxylase deficiency with salt-wasting crisis. The enzyme block shunts substrate to androgens (virilization of XX) and reduces both cortisol AND aldosterone. Hyponatremia + hyperkalemia + hypotension + hypoglycemia reflect mineralocorticoid and glucocorticoid deficiency. Emergency management: volume resuscitation + hydrocortisone (glucocorticoid, also some mineralocorticoid activity) + fludrocortisone (mineralocorticoid). 17-OH-progesterone is the screening marker. Genitoplasty (E) is elective and delayed.
Question 4 of 6 — Complete Androgen Insensitivity
A 16-year-old phenotypically female adolescent presents with primary amenorrhea. She is tall with normal breast development (Tanner V), scant axillary and pubic hair (Tanner II), and a blind-ending vagina on pelvic exam. Imaging reveals absence of the uterus and ovaries, with bilateral intra-abdominal testes. Serum testosterone is 650 ng/dL (high normal for adult male), LH is elevated, and estradiol is elevated. Karyotype is 46,XY. Which of the following best explains her phenotype?
ADeficient 5α-reductase activity in peripheral tissues
BSertoli cell failure to secrete Müllerian inhibiting substance (MIS)
CDefective androgen receptor preventing normal testosterone signaling
DAbsence of the SRY gene due to translocation
E21-hydroxylase deficiency with chronic ACTH stimulation
C — Defective androgen receptor. Classic complete androgen insensitivity syndrome (CAIS). The testes form normally (SRY present), Sertoli cells secrete MIS → no Müllerian derivatives (no uterus, no upper vagina). Leydig cells secrete testosterone, but tissues can't respond → no Wolffian derivatives AND no external virilization → phenotypically female. Testosterone is aromatized to estradiol in the periphery → breast development at puberty. Scant pubic/axillary hair because hair follicles also can't respond to androgens. 5α-reductase deficiency (A) would produce a different pattern with ambiguous genitalia at birth that virilizes at puberty.
Question 5 of 6 — Cryptorchidism Management
A 9-month-old boy is noted during a well-child visit to have a left testis that cannot be palpated in the scrotum or along the inguinal canal. Pediatric urology ultrasound identifies the testis in the abdomen. Which of the following is the most important reason to proceed with orchidopexy now rather than wait until adolescence?
AThe testis is unlikely to descend spontaneously and will require lifelong hormone therapy
BEarly repair reduces the risk of infertility and testicular germ cell malignancy (seminoma)
CThe testis produces no testosterone until it is moved into the scrotum
DUndescended testes always cause severe pain and inguinal hernias by age 2
EDelay beyond 1 year always causes testicular torsion
B — Early repair ↓ infertility and seminoma risk. Spermatogenesis is heat-sensitive; the scrotum maintains testicular temperature ~2°C below core body temp. Undescended testes undergo progressive germ cell loss in the first two years of life, so orchidopexy is recommended by 6 months (no later than 12 months). Even after repair, risk of seminoma remains elevated — but earlier surgery lowers that risk and permits easier surveillance. Testosterone (C) is still produced by undescended testes (Leydig cells intact). Torsion risk is increased but not universal (E).
Question 6 of 6 — Hypospadias
A newborn boy is noted on exam to have an abnormal urethral opening on the ventral (underside) surface of the penile shaft, approximately halfway between the glans and the scrotum. The foreskin is dorsally hooded. He is otherwise healthy with no other congenital anomalies. Which of the following embryologic events explains this finding?
AFailure of labioscrotal swellings to fuse
BFailure of the urethral (urogenital) folds to fuse along the ventral aspect of the penis
CAbnormal dorsal positioning of the genital tubercle with bladder exstrophy
DFailure of the processus vaginalis to obliterate
EPersistence of the allantois between bladder and umbilicus
B — Failure of urethral folds to fuse ventrally. This is classic hypospadias. Normally, DHT drives the urethral (urogenital) folds to fuse along the ventral midline, enclosing the urethral groove to create the penile urethra. When fusion is incomplete, the urethra opens on the ventral surface — anywhere from glanular (most common) to penoscrotal (more severe). Do NOT circumcise an infant with hypospadias — the foreskin is used in the surgical repair (urethroplasty, usually by 6–12 months). Dorsal positioning with bladder exstrophy (C) describes epispadias, a distinct and less common anomaly. Labioscrotal fusion failure (A) → bifid scrotum.
Ordering Drills: Arrange each sequence of steps in the correct physiologic or pathologic order. Drag items to reorder. Click "Check Order" to verify, or "Show Answer" to reveal the correct sequence.
Male Sexual Differentiation — SRY to External Genitalia
Trace the hormonal and anatomic cascade from the Y chromosome to a phenotypic male.
Leydig cells secrete testosterone → stabilize Wolffian ducts (SEED)
Order the steps of testicular descent, and how failure produces cryptorchidism & hydrocele.
Testis descends through the inguinal canal into scrotum (~wk 28)
Testis develops in the posterior abdominal wall (retroperitoneal)
Processus vaginalis obliterates after descent (partial remnant = tunica vaginalis)
Processus vaginalis (peritoneal outpouching) forms ahead of the testis
Gubernaculum tethers inferior pole of testis to labioscrotal swelling
Failure at any step → cryptorchidism; patent PV → communicating hydrocele / indirect hernia
Testis develops in the posterior abdominal wall (retroperitoneal)
Gubernaculum tethers inferior pole of testis to labioscrotal swelling
Processus vaginalis (peritoneal outpouching) forms ahead of the testis
Testis descends through the inguinal canal into scrotum (~wk 28)
Processus vaginalis obliterates after descent (partial remnant = tunica vaginalis)
Failure at any step → cryptorchidism; patent PV → communicating hydrocele / indirect hernia
Vignette MCQs: Clinical scenarios testing disease recognition and mechanisms. Select your best answer and the explanation appears automatically.
Vignette 1 of 4 — 5α-Reductase Deficiency
A 13-year-old "girl" who was raised female since birth now presents with deepening voice, growth of a phallus, and appearance of testes in the labioscrotal folds. Karyotype is 46,XY. Serum testosterone is elevated for age; DHT is low. The T:DHT ratio is markedly increased. Pelvic imaging shows no uterus, no ovaries, and intra-abdominal testes with normal epididymides and vasa deferentia.
AComplete androgen insensitivity syndrome
B5α-reductase deficiency
C21-hydroxylase deficiency
DKlinefelter syndrome
ESwyer syndrome (pure XY gonadal dysgenesis)
B — 5α-reductase deficiency. Buzzwords: 46 XY, normal internal male structures (epididymis/vas), female/ambiguous external genitalia at birth, virilization at puberty, ↑ T:DHT ratio. Testosterone maintains Wolffian (internal) structures — those are normal. DHT masculinizes external genitalia — those cannot develop without DHT until the testosterone surge at puberty drives virilization directly. CAIS (A) would have NO Wolffian structures (receptor doesn't work) and breasts (aromatization).
Vignette 2 of 4 — Ectopic Ureter
A 5-year-old girl has had continuous dribbling/wetting since birth despite otherwise normal daytime voiding. Bedwetting persists nightly. Renal ultrasound shows a duplicated collecting system on the left. VCUG is unremarkable. MR urography demonstrates a ureter draining from the upper pole of the left kidney into the vestibule of the vagina, below the external urethral sphincter.
APosterior urethral valves
BVesicoureteral reflux
CEctopic ureter
DUreterocele
EUrethral diverticulum
C — Ectopic ureter. Buzzwords: continuous dribbling + normal voiding, girl, duplicated collecting system, draining below external sphincter. Incomplete absorption of the mesonephric duct → ureteric bud implants abnormally low. In girls, the ectopic ureter can drain into the vagina, vestibule, or distal urethra (all below the sphincter) → constant leak. The otherwise-normal bladder and sphincter provide normal voiding. Weigert-Meyer rule: in a duplex system, the upper-pole ureter is the ectopic one (drains ectopically/low); the lower-pole ureter refluxes. Posterior urethral valves (A) affects boys only.
Vignette 3 of 4 — ADPKD
A 44-year-old man with a strong family history of hypertension and renal failure is found to have BP 168/104 mmHg. Urinalysis shows 2+ blood without infection. Abdominal exam is notable for bilateral palpable flank masses. Renal ultrasound demonstrates multiple cysts of varying sizes in both kidneys, with several cysts also in the liver. He suddenly develops the "worst headache of his life" and is admitted.
AMulticystic dysplastic kidney (MCDK)
BARPKD (autosomal recessive)
CADPKD (autosomal dominant) with ruptured berry aneurysm
DMedullary sponge kidney
ESimple bilateral renal cysts
C — ADPKD + subarachnoid hemorrhage. Buzzwords: family history, hypertension, bilateral cystic kidneys, hepatic cysts, "worst headache of life". ADPKD is caused by mutations in PKD1 (chr 16) or PKD2; presents in adulthood. Associated with berry aneurysms (Circle of Willis → SAH), mitral valve prolapse, hepatic/pancreatic cysts, and diverticulosis. ARPKD (B) presents in infancy with Potter sequence and hepatic fibrosis. MCDK (A) is unilateral, sporadic, and NOT inherited.
Vignette 4 of 4 — Klinefelter Syndrome
A 17-year-old tall, thin male presents with bilateral gynecomastia, small firm testes, and learning difficulties. Puberty started late and is incompletely developed. He reports a friend's comment that he has a "eunuchoid" body habitus. Serum testosterone is low-normal, LH and FSH are markedly elevated, and estradiol is increased. Semen analysis shows azoospermia. Karyotype confirms 47,XXY.
ATurner syndrome
BKallmann syndrome
CKlinefelter syndrome
DComplete androgen insensitivity
E5α-reductase deficiency
C — Klinefelter syndrome (47 XXY). Buzzwords: tall, eunuchoid, gynecomastia, small firm testes, ↑ LH/FSH, ↑ estradiol, azoospermia. Seminiferous tubules degenerate → ↓inhibin, ↑FSH; Leydig cells also dysfunction → ↓T, ↑LH. Peripheral aromatization of testosterone → ↑estradiol → gynecomastia. Risk of breast cancer and extragonadal germ cell tumors is elevated. Testosterone replacement is standard treatment. Turner syndrome (A) is 45,X and female.
Step 1 Traps: Common false statements that appear plausible but are incorrect. Choose the correct answer to reveal the trap explanation.
Trap 1 of 7
In complete androgen insensitivity syndrome (CAIS), patients have a uterus and fallopian tubes because Müllerian ducts require androgens to regress.
Müllerian ducts are regressed by MIS/AMH from Sertoli cells — this is INDEPENDENT of the androgen receptor. In CAIS, Sertoli cells are still functional and secrete MIS → Müllerian ducts regress normally. CAIS patients therefore have NO uterus and NO upper vagina (blind-ending vagina). It's the WOLFFIAN derivatives (testosterone-dependent) that are absent in CAIS.
Trap 2 of 7
A horseshoe kidney typically gets stuck in the pelvis because the inferior mesenteric artery (IMA) blocks its ascent.
A horseshoe kidney is blocked by the IMA, but it sits at about the L3–L4 level, not in the pelvis. Pelvic kidney is a different anomaly — a unilateral kidney that fails to ascend at all. Don't conflate. Horseshoe kidney is classically associated with Turner syndrome (45,X) and trisomy 18.
Trap 3 of 7
All forms of congenital adrenal hyperplasia (CAH) cause salt-wasting and hypotension.
Only 21-hydroxylase deficiency (95% of CAH) causes salt-wasting and hypotension. 11β-OH deficiency and 17α-OH deficiency both cause HYPERTENSION and hypokalemia (from mineralocorticoid buildup — 11-deoxycorticosterone in 11β, and the full mineralocorticoid pathway in 17α). Mnemonic: "11 and 17 → HTN; 21 → hypoTN." 17α also blocks ALL sex steroid synthesis → XY has female phenotype and XX has no 2° sex characteristics.
Trap 4 of 7
Potter sequence babies die from renal failure shortly after birth because their kidneys cannot excrete waste.
The cause of death is pulmonary hypoplasia, not renal failure. Fetal kidneys produce amniotic fluid in T2; without them → oligohydramnios → lungs fail to mature → respiratory failure immediately after birth. Dialysis doesn't work because the lungs cannot oxygenate. The P in POTTER stands for "Pulmonary hypoplasia" — the killer.
Trap 5 of 7
Testosterone is responsible for masculinizing the external genitalia during fetal development.
Easily missed distinction. DHT (not testosterone) masculinizes the EXTERNAL genitalia. Testosterone maintains the INTERNAL Wolffian duct derivatives (epididymis, vas deferens, seminal vesicles). That's why in 5α-reductase deficiency (can't make DHT), a 46 XY has female-looking external genitalia but normal internal male structures. DHT = external; Testosterone = internal.
Trap 6 of 7
Orchidopexy should be delayed until at least puberty to allow testicular maturation before surgical intervention.
Orchidopexy for cryptorchidism should be performed by 6 months of age (no later than 12 months). Waiting until puberty massively ↑ risks of infertility (heat damage to germ cells) and seminoma. Contrast with complete AIS, where gonadectomy IS delayed until after puberty — but for a different reason (testes drive feminization through aromatization to estradiol).
Trap 7 of 7
The trigone of the bladder is derived from the urogenital sinus (endoderm), just like the rest of the bladder.
The trigone is MESODERMAL — derived from absorbed mesonephric (Wolffian) ducts during weeks 5–6. The rest of the bladder (dome, walls) is endodermal (from urogenital sinus). This mixed-origin bladder explains why the trigone is smooth and triangular (unlike the rugated bladder walls). The same process forms the openings of the ureters and urethra at the three corners of the trigone.
Reference Tables: Quick-lookup tables for urogenital developmental anomalies, DSDs, and enzyme defects. Print-friendly format.
Disorders of Sexual Differentiation — Differential Grid
Condition
Karyotype
Internal
External
Testosterone
Key Feature
Complete AIS
46 XY
No uterus; testes intra-abdominal
Female, blind vagina
↑ T, ↑ LH, ↑ estradiol
Defective androgen receptor; breasts at puberty
5α-reductase def
46 XY
Normal Wolffian (epididymis, vas)
Ambiguous/female at birth → virilizes at puberty
Normal T, ↓ DHT, ↑ T:DHT ratio
"Penis at 12" — Dominican "guevedoces"
21-OH def (CAH)
46 XX
Normal female internal
Virilized/ambiguous
↑ adrenal androgens, ↑ 17-OH-prog
Salt wasting, hypoTN, hypoNa, hyperK
11β-OH def
46 XX
Normal female internal
Virilized
↑ adrenal androgens, ↑ 11-deoxycortico.
HTN (not salt-wasting)
17α-OH def
XX or XY
XY: no Wolffian derivatives
Female phenotype in both; no 2° sex char.
↓ sex hormones, ↑ mineralocorticoids
HTN + hypoK + NO puberty
Klinefelter (XXY)
47 XXY
Internal male
Tall, eunuchoid, gynecomastia, small testes
↓ T, ↑ LH/FSH, ↑ E2
Azoospermia; aromatization
Turner (45 XO)
45 XO
Streak ovaries, normal uterus
Short, webbed neck, shield chest
↓ estrogen, ↑ LH/FSH
Horseshoe kidney, coarctation, BAV
Swyer (pure XY dysgenesis)
46 XY
Normal Müllerian (no MIS); streak gonads
Female
↓ T (streak gonads)
Has uterus — can carry pregnancy with donor egg; gonadectomy recommended (gonadoblastoma risk)
Male vs Female Homologous Structures — Quick Reference
Embryonic Origin
Male Derivative
Female Derivative
Genital tubercle
Glans/shaft of penis
Clitoris
Urogenital (urethral) folds
Penile urethra (fuse)
Labia minora (unfused)
Labioscrotal swellings
Scrotum (fuse; raphe)
Labia majora (unfused)
Gonad
Testis
Ovary
Gubernaculum
Gubernaculum testis (cord)
Round lig. of uterus + ovarian ligament
Urogenital sinus (prostate)
Prostate gland
Skene's (paraurethral) glands
Bulbourethral
Cowper's glands
Bartholin's (greater vestibular) glands
Müllerian remnant
Prostatic utricle, appendix testis
Uterus + upper 2/3 vagina (persists)
Wolffian remnant
SEED (Seminal, Epididymis, Ejac. duct, vas Deferens) + trigone
Gartner's duct cyst, trigone
Memory aid: Wolffian = "Will develop" with testosterone (♂); Müllerian = "Mama, don't need T" (default ♀)
High-Yield Testing Notes: Key patterns to recognize on exams. Badges indicate trap concepts, buzzword clusters, and testing-focused insights.
TESTING Metanephric Blastema vs Ureteric Bud — Who Makes What
Common Step 1 distinction: the metanephric blastema (mesoderm) forms the NEPHRON (Bowman's, PCT, LOH, DCT), while the ureteric bud (an outgrowth of the Wolffian duct) forms the COLLECTING SYSTEM (collecting ducts, calyces, pelvis, ureter). Reciprocal induction between the two is essential — defects produce MCDK. Memorize which structures come from which source: if glomerulus/nephron → blastema; if collecting plumbing → bud.
TRAP The Potter Sequence COD Trap
Students often assume death in Potter sequence is from renal failure. It's actually from pulmonary hypoplasia → respiratory failure. Fetal urine makes amniotic fluid, which is required for lung maturation in weeks 16–26. Without kidneys → no amniotic fluid → lungs can't develop. This is the #1 testable fact for bilateral renal agenesis / bilateral MCDK / ARPKD → always check: "what kills the baby?" → pulmonary.
Vignette cluster: short stature + webbed neck + primary amenorrhea + bicuspid aortic valve/coarctation + horseshoe kidney → Turner syndrome (45 XO). Second cluster: clenched fist with overlapping fingers + rocker-bottom feet + micrognathia + horseshoe kidney → Trisomy 18 (Edwards). The kidney is caught at L3–L4 by the IMA — don't say "pelvis," that's a different anomaly (pelvic kidney).
TESTING CAH — 21 vs 11β vs 17α
Three enzyme deficiencies, three different pictures. 21-OH (95%): virilization + hypoTN + salt wasting (hypoNa, hyperK). 11β-OH: virilization + HTN (excess 11-deoxycorticosterone). 17α-OH: no sex steroids (XY = female phenotype; XX = no 2° sex char.) + HTN. Mnemonic: "11 & 17 → HTN; 21 → hypoTN." Also: "17 hits sex; 11 & 21 virilize." The screening lab for 21-OH is 17-OH-progesterone — tested in every newborn screen in the US.
TRAP AIS vs 5α-Reductase — Key Differences at Puberty
Both are 46 XY with female-appearing external genitalia. Differentiate by (1) Internal structures: AIS has NO Wolffian derivatives (no receptor); 5α-reductase has intact Wolffian (T works — just no DHT). (2) Puberty: AIS develops BREASTS (aromatization) but no virilization; 5α-red VIRILIZES dramatically ("penis at 12") — no breasts. (3) Hormones: AIS = ↑T, ↑LH, ↑E2; 5α-red = normal T, ↑ T:DHT ratio. Gonadectomy timing: AIS after puberty (for feminization); 5α-red may preserve gonads if raised male.
BUZZWORD Ectopic Ureter — "Continuous Dribbling + Normal Voiding"
A school-age girl with constant wetness DESPITE normal voiding → ectopic ureter draining below the external urethral sphincter. Image-wise, look for duplex collecting system (Weigert-Meyer: upper-pole ureter ectopic, lower-pole ureter refluxes). Path: failed mesonephric duct absorption → ureteric bud implanted too low. Boys rarely have this picture because male ectopic ureters drain into the Wolffian derivatives (vas, seminal vesicle) — above the sphincter.
TESTING DHT vs T — Internal vs External
Highly tested: Testosterone maintains INTERNAL structures (Wolffian: SEED → Seminal vesicle, Epididymis, Ejaculatory duct, vas Deferens). DHT masculinizes EXTERNAL structures (penis, scrotum, prostate). This is why 5α-reductase deficiency produces normal INTERNAL male anatomy with FEMALE external genitalia. It also explains DHT-targeted drugs: finasteride (5α-reductase inhibitor) treats BPH and androgenetic alopecia (external DHT effects) while preserving internal testosterone-dependent functions.
Clinical Correlates: Review key disease profiles and clinical connections. Click "Show" to reveal comparison details.
Developmental Kidney Anomalies
ADPKD vs ARPKD vs MCDK — Key Distinguishing Features
All three produce cystic kidneys but differ in genetics, timing, and associations.
ARPKD (autosomal recessive):PKHD1; infantile; may cause Potter sequence in utero; classic: bilateral enlarged kidneys + congenital hepatic fibrosis → portal HTN/splenomegaly.
MCDK (sporadic, not inherited):failed ureteric bud ↔ metanephric blastema interaction during initial kidney formation; usually unilateral (asymptomatic); bilateral = Potter sequence.
Feature
ADPKD
ARPKD
MCDK
Genetics
AD; PKD1/PKD2
AR; PKHD1
Sporadic
Age
Adults
Infancy
Prenatal
Extrarenal
Berry aneurysm, MVP, liver cysts
Hepatic fibrosis
VACTERL assoc.
Prognosis
CKD by 60
Often fatal in infancy
Unilat OK; bilat → Potter
Disorders of Sexual Differentiation
The 46 XY with "Female" Phenotype — CAIS vs 5α-Red vs Swyer
Three distinct entities all featuring 46 XY karyotype with discordant phenotype:
Complete AIS: Defective androgen receptor. Female external appearance, breasts at puberty (aromatization), no uterus (MIS intact), blind vagina. ↑T, ↑LH, ↑E2.
5α-reductase deficiency: Can't make DHT. Female/ambiguous at birth, dramatic virilization at puberty ("penis at 12"), has internal male anatomy (Wolffian derivatives present). Normal T, ↑ T:DHT ratio.
Swyer syndrome (pure XY gonadal dysgenesis): SRY failure or downstream defect → streak gonads → no MIS and no T. Has a uterus — can carry pregnancy via donor egg + hormonal support. Presents as "tall female with primary amenorrhea." Gonadectomy required (gonadoblastoma risk).
USMLE Clue Words:
• "Tall female with primary amenorrhea + breasts + no pubic hair" → CAIS
• "Raised female, virilizes at puberty" / "penis at 12" → 5α-reductase deficiency
• "Female with primary amenorrhea + has a uterus + streak gonads" → Swyer
• Gonadectomy timing: AIS after puberty (for feminization); Swyer → immediate (gonadoblastoma); Cryptorchidism → orchidopexy before 12 months (seminoma risk)
Congenital Adrenal Hyperplasia
21-OH vs 11β-OH vs 17α-OH — Sex Hormones + BP Triangulation
Three CAH enzyme deficiencies tested as BP + virilization patterns:
21-hydroxylase deficiency (95%): Loss of cortisol + aldosterone → salt wasting, hypoTN, hypoNa, hyperK. Androgen shunt → XX virilization. ↑ 17-OH-progesterone on screen. Tx: hydrocortisone + fludrocortisone.
11β-hydroxylase deficiency: Loss of cortisol; 11-deoxycorticosterone accumulates → weak mineralocorticoid → HTN + hypoK. Androgens also shunted → virilization. Tx: hydrocortisone.
17α-hydroxylase deficiency: Loss of ALL sex hormones + cortisol. Mineralocorticoid pathway preserved → HTN + hypoK. XY → female phenotype (no T); XX → normal female but no 2° sex development at puberty. Tx: hydrocortisone + sex steroid replacement.
Memory aids:
• "11 & 17 → HTN; 21 → hypoTN"
• "17 hits sex steroids; 11 & 21 cause virilization"
• Screening lab for 21-OH: 17-hydroxyprogesterone (mandatory US newborn screen)
• GFR = Salty, Sweet, Sexy: Glomerulosa (aldosterone) · Fasciculata (cortisol) · Reticularis (androgens)
Urogenital Derivatives + Boards
Wolffian vs Müllerian — Which Hormone Controls Which?
The most testable concept in urogenital embryology:
Wolffian (mesonephric) duct → SEED: Requires testosterone to persist. In ♂ → Seminal vesicles, Epididymis, Ejaculatory duct, Ductus (vas) deferens (+ trigone). In ♀ (no T) → degenerates (remnant = Gartner's duct cyst).
Müllerian (paramesonephric) duct → Female internal tract: Persists by DEFAULT. Regressed by MIS/AMH from Sertoli cells. In ♀ → fallopian tubes, uterus, cervix, upper 2/3 vagina. In ♂ → degenerates (remnants = prostatic utricle, appendix testis).
External genitalia: Controlled by DHT (5α-reductase-converted T). No DHT = default female (clitoris, labia). DHT present = male (penis, scrotum, prostate).
What this explains on Step 1:
• CAIS (46 XY): No T signal → no Wolffian derivatives. But MIS works → no Müllerian. Result: no internal genitalia either way + female external.
• 5α-reductase deficiency: T works → Wolffian present. MIS works → no Müllerian. But no DHT → female external at birth. At puberty, T alone (high dose) partially masculinizes externals.
• Swyer syndrome: No SRY → no Sertoli → no MIS → Müllerian persists (uterus). No T → no Wolffian. Female external by default. Can carry a pregnancy!
• Müllerian agenesis (46 XX, MRKH): ↓ Müllerian formation → no uterus/upper vagina, but normal ovaries. Primary amenorrhea with normal 2° sex char.