Ambiguous Genitalia (Disorders of Sex Development)

Embryology

• The SRY gene (sex-determining region of the Y chromosome, located on the short arm) acts as the genetic switch that initiates gonadal differentiation toward the male phenotype
• Sertoli cells secrete Mullerian-Inhibiting Substance (MIS / AMH), causing regression of the Mullerian duct (which would form the uterus, fallopian tubes, upper vagina)
• Testosterone from Leydig cells virilizes the Wolffian ducts into vas deferens, epididymis, seminal vesicles
• Dihydrotestosterone (DHT) (converted from testosterone by 5α-reductase) virilizes the external genitalia
• In the absence of SRY, MIS is not produced, Mullerian structures are preserved, and the female phenotype is the default

Classification

1. 46,XX DSD (Overvirilized Female / Female Pseudohermaphroditism)

• Most common overall cause of ambiguous genitalia
• Ovaries present, no testes
• Congenital Adrenal Hyperplasia (CAH) is the most common cause (90% due to 21-hydroxylase deficiency)
  • Also: 11-hydroxylase deficiency, 3β-hydroxysteroid dehydrogenase deficiency
  • Excess adrenal androgens virilize the female fetus
  • Karyotype 46,XX; prone to salt-wasting crisis (requires cortisol + fludrocortisone replacement)
• Other causes: maternal androgen-secreting tumor, exogenous androgens

2. 46,XY DSD (Undervirilized Male / Male Pseudohermaphroditism)

• Testes present, but deficient masculinization of external genitalia
• Causes include:
  • Androgen insensitivity syndrome (AIS / testicular feminization) - defective androgen receptors; testes may be found incidentally during herniorrhaphy in a phenotypic female
  • 5α-reductase deficiency - cannot convert testosterone to DHT; phenotypic female at birth but virilizes at puberty
  • Testosterone biosynthesis disorders (enzymatic defects)
  • Testicular regression syndrome
  • Absence/mutation of SRY

3. True Hermaphroditism (Ovotesticular DSD)

• Rarest form
• Both ovarian and testicular tissue present (ovary on one side, testis on the other, or ovotestis)
• Majority have 46,XX karyotype
• Both the testis and testicular portion of ovotestis should be removed

4. Mixed Gonadal Dysgenesis

• Dysgenetic gonads + retained Mullerian structures
• Typical karyotype is mosaic: 45,XO / 46,XY
• High risk of gonadoblastoma in dysgenetic gonads
• Associated with features of Turner syndrome

Clinical Findings Suspicious for DSD (Harriet Lane)

• Apparent female with clitoromegaly (length >1 cm or width >6 mm at term)
• Inguinal or labial mass
• Posterior labial/scrotal fusion
• Micropenis (stretched penile length <2.5 SD below mean for age; full-term mean = 3.5 ± 0.4 cm)
• Nonpalpable gonads in an apparent male
• Hypospadias with undescended testis or scrotal separation
• Discordance between prenatal karyotype and genital appearance

Note: A patient with bilaterally impalpable testes + hypospadias should be considered to have a DSD until proven otherwise, even without obvious ambiguity. The incidence of DSD in this group is ~30% overall, rising to ~50% with impalpable testes (Campbell Walsh Urology).

Evaluation - A Medical and Psychosocial Emergency

Physical Examination

Laboratory Investigations

Imaging

• Pelvic ultrasonography: Assess Mullerian anatomy, gonads, adrenal glands; rule out ovotestis cyst
• Retrograde contrast injection (genitogram): Defines urogenital sinus anatomy, entry of urethra and vagina - necessary before any surgery
• MRI: Detailed anatomic evaluation

Diagnostic Algorithm Based on Initial Findings

Ambiguous Genitalia
        |
  ┌─────┴─────┐
Gonads         Gonads NOT
palpable       palpable
  |                 |
46,XY DSD      Karyotype + 17-OHP
(undervirilized       |
   male)       ┌─────┴──────┐
              46,XX        46,XY
              + elevated    DSD (gonadal
              17-OHP        dysgenesis,
              → CAH         AIS, etc.)

Management

Sex Assignment

• Assign sex of rearing based on: precise diagnosis, anatomical status, functional potential of genitalia, and reproductive tract
• A definitive diagnosis is achievable in virtually all 46,XX DSD but in <50% of 46,XY DSD
• Laparoscopy/laparotomy + gonadal biopsy may be needed if diagnosis cannot be made from initial workup (removal of gonads deferred until pathology confirmed)

Medical

• CAH (46,XX): Glucocorticoid replacement (cortisol) to suppress adrenal androgens; mineralocorticoid (fludrocortisone) if salt-wasting
• AIS: Gonadectomy after puberty (to allow feminizing puberty from peripheral estrogen conversion), then hormone replacement
• 5α-reductase deficiency: Many patients virilize at puberty and may prefer male gender role
• Mixed gonadal dysgenesis: Gonadectomy due to high risk of gonadoblastoma

Surgical

• Goals: functional external genitalia consistent with gender assignment, preservation of fertility potential, elimination of malignancy risk
• Timing and type of surgery are individualized and increasingly defer to patient autonomy
• Clitoroplasty/vaginoplasty for virilized females
• Hypospadias repair + orchiopexy for undervirilized males
• Testes in AIS / male pseudohermaphroditism should be resected due to malignant degeneration risk

Key Points Summary

• Ambiguous genitalia is a neonatal emergency - do not delay sex assignment without full evaluation
• The most common cause is CAH (21-hydroxylase deficiency) in a 46,XX female
• Never announce sex at birth until evaluation is complete
• Involve the family in all discussions and decisions
• The modern approach favors delaying irreversible surgery when possible, with input from the patient

A 2025 Nature Reviews Disease Primers review (PMID 40744924) provides a current comprehensive overview of differences of sex development.

• Schwartz's Principles of Surgery, 11th Ed.
• Campbell Walsh Wein Urology (Chapter 48: Evaluation and Management of the Newborn with Ambiguous Genitalia)
• The Harriet Lane Handbook, 23rd Ed. (Johns Hopkins Hospital)