A 19-year-old unmarried girl from Mumbai presents with primary amenorrhea. She has never menstruated. On examination, she is 162 cm tall, weighs 48 kg (BMI 18.3), and appears well-developed. Breast development is Tanner stage 5, pubic hair is Tanner stage 5, and axillary hair is present. External genitalia appear normal on inspection. Pelvic examination reveals a blind-ending vaginal pouch; the cervix, uterus, and ovaries are not palpable. Abdominal ultrasound shows no uterus or fallopian tubes, but bilateral ovaries with normal follicles are visualized. Serum FSH is 6.8 mIU/mL, LH is 7.2 mIU/mL, and estradiol is 45 pg/mL (normal follicular phase). Karyotype is 46,XX. What is the most likely diagnosis?

Explanation

## Clinical Analysis This patient presents with **primary amenorrhea** (never menstruated) with normal secondary sexual characteristics but absent uterus, fallopian tubes, and upper vagina. ### Key Diagnostic Features **Key Point:** The combination of **46,XX karyotype + normal ovarian function (normal FSH/LH/estradiol) + absent uterus, fallopian tubes, and upper vagina + blind-ending vaginal pouch** is pathognomonic for **Müllerian agenesis (MRKH syndrome)**. ### Differential Diagnosis Table | Feature | MRKH | AIS | Gonadal Dysgenesis | TFS | |---------|------|-----|-------------------|-----| | **Karyotype** | 46,XX | 46,XY | 45,X or mosaic | 46,XY | | **Gonads** | Normal ovaries | Testes | Streak gonads | Testes | | **FSH/LH** | Normal | Normal/low | Elevated | Normal/low | | **Estradiol** | Normal | Low | Low | Low | | **External genitalia** | Female | Female | Female | Female | | **Uterus** | Absent | Absent | Absent | Absent | | **Vagina** | Blind pouch | Short/absent | Blind pouch | Short/absent | | **Pubic/axillary hair** | Present | Absent/sparse | Absent/sparse | Absent/sparse | ### Why Müllerian Agenesis (MRKH)? 1. **46,XX karyotype** — Rules out androgen insensitivity syndrome (46,XY) and testicular feminization (46,XY). 2. **Normal secondary sexual characteristics** — Breast and pubic hair development at Tanner stage 5 indicates normal estrogen production and androgen responsiveness. 3. **Normal ovarian function** — FSH, LH, and estradiol are all in normal range, confirming functional ovaries. 4. **Absent Müllerian structures** — No uterus, fallopian tubes, or upper vagina; only a blind-ending vaginal pouch. This is the hallmark of Müllerian agenesis. 5. **Normal external genitalia** — Excludes androgen insensitivity (which presents with absent pubic/axillary hair and female external genitalia with 46,XY karyotype). **High-Yield:** **MRKH syndrome** is the second most common cause of primary amenorrhea (after gonadal dysgenesis) and is characterized by congenital absence of the uterus and upper 2/3 of the vagina in 46,XX individuals with normal ovarian function and normal secondary sexual development. **Mnemonic:** **MRKH = Müllerian agenesis = Mayer–Rokitansky–Küster–Hauser** — remember the four eponymous physicians. ### Embryologic Basis ```mermaid flowchart TD A[Müllerian ducts]:::outcome --> B{Normal development?}:::decision B -->|Yes| C[Fallopian tubes, uterus, upper vagina]:::outcome B -->|No| D[Müllerian agenesis]:::outcome D --> E[Absent uterus + tubes + upper vagina]:::outcome E --> F[Primary amenorrhea + blind vaginal pouch]:::outcome A --> G[Ovaries develop from mesonephros - independent of Müllerian ducts]:::outcome G --> H[Normal ovarian function preserved]:::outcome ``` **Clinical Pearl:** Patients with MRKH syndrome have **normal fertility potential via assisted reproductive technologies** (oocyte retrieval and embryo transfer to a surrogate or uterine transplant). They require counseling about sexual function and reproductive options. ### Management - **Diagnosis confirmation:** Pelvic MRI or ultrasound (as done here). - **Associated anomalies:** Screen for renal and skeletal abnormalities (present in ~30% of MRKH cases). - **Counseling:** Discuss sexual function, fertility options (surrogacy, uterine transplant). - **Psychological support:** Address impact of infertility diagnosis in a young woman.