A 16-year-old girl presents with primary amenorrhea. She has normal secondary sexual characteristics, normal height, and a normal external genitalia examination. On pelvic examination, the uterus is absent. What is the investigation of choice to confirm the diagnosis?

Explanation

## Clinical Scenario Analysis This patient presents with: - Primary amenorrhea (no menarche by age 16) - Normal secondary sexual characteristics (normal FSH/LH signalling) - Normal height and external genitalia - Absent uterus on clinical examination This clinical picture is classic for **Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome, MRKH)** — a congenital absence or underdevelopment of the uterus and upper 2/3 of the vagina. ## Investigation of Choice **Key Point:** **Pelvic ultrasound** is the **investigation of choice** (first-line investigation) for confirming the diagnosis of Müllerian agenesis / MRKH syndrome. It is non-invasive, widely available, cost-effective, and can readily confirm the absence of the uterus while also visualizing the ovaries and kidneys. According to standard OBG textbooks (Shaw's Gynaecology, Dutta's Textbook of Gynaecology), **pelvic ultrasound** is the recommended initial investigation in the workup of primary amenorrhea with suspected Müllerian anomalies. ## Investigation Hierarchy | Investigation | Role | Limitation | |---|---|---| | **Pelvic ultrasound** | **First-line / Investigation of choice**; confirms absent uterus, visualizes ovaries and kidneys | Limited soft-tissue definition compared to MRI | | **MRI pelvis** | Gold standard for characterization; superior soft-tissue resolution; detects full spectrum of Müllerian anomalies and associated renal/spinal defects | High cost; reserved for complex cases or pre-surgical planning | | **Hysterosalpingography** | Requires patent cervix; not useful if uterus absent | Invasive; cannot assess upper vagina or renal system | | **Diagnostic laparoscopy** | Invasive; surgical | Unnecessary when imaging is diagnostic | ## Why Pelvic Ultrasound Is Correct **High-Yield:** Pelvic ultrasound provides: 1. Confirmation of absent/hypoplastic uterus 2. Visualization of ovaries (normal in MRKH — ovarian function is intact) 3. Assessment of kidneys (renal anomalies occur in 30–40% of MRKH cases) 4. Non-invasive, readily available, and cost-effective **Clinical Pearl:** While MRI pelvis is the **gold standard** for detailed characterization of Müllerian anomalies and pre-surgical planning, **pelvic ultrasound is the investigation of choice** for initial confirmation of the diagnosis. MRI is reserved for cases where ultrasound findings are inconclusive or when detailed anatomical mapping is required before surgical intervention. In NEET PG and standard Indian OBG curricula (Dutta, Shaw), pelvic ultrasound is consistently cited as the first-line investigation of choice for primary amenorrhea workup. ## Associated Findings in MRKH **Mnemonic: MRKH Associations** - **M**üllerian agenesis (uterus/upper vagina absent) - **R**enal anomalies (30–40%: unilateral agenesis, ectopia, dysplasia) - **K**yphoscoliosis or skeletal defects (10–15%) - **H**earing loss (rare; Rokitansky syndrome variant) Ovarian function is **normal** (normal FSH/LH axis); secondary sexual characteristics develop normally, as seen in this patient. *(Reference: Dutta's Textbook of Gynaecology, 9th ed.; Shaw's Textbook of Gynaecology, 17th ed.)*