## Clinical Context: Anatomical Causes of Primary Amenorrhea with Normal Pelvic Ultrasound This patient has **primary amenorrhea with normal secondary sexual characteristics, normal external genitalia, and a normal pelvic ultrasound showing a uterus and ovaries** — the key discriminating feature is the **presence of a normal uterus on imaging**. ### Why Müllerian Agenesis Is the EXCEPT Answer **Key Point:** Müllerian agenesis (MRKH syndrome — Mayer-Rokitansky-Küster-Hauser syndrome) is characterized by **congenital absence or severe hypoplasia of the uterus and upper vagina** due to failure of müllerian duct development. The uterus is **absent or rudimentary**, not normal. In this clinical scenario: - The pelvic ultrasound shows a **normal uterus and ovaries** - Müllerian agenesis would produce an **absent or rudimentary uterus** — directly contradicting the imaging findings - Therefore, Müllerian agenesis **cannot be the cause** in this patient ### Analysis of All Options | Diagnosis | Uterus on Ultrasound | Cause of Primary Amenorrhea? | Compatible with Stem? | |---|---|---|---| | **Asherman's syndrome** | Present (normal) | Typically secondary, but rare congenital forms exist; outflow obstruction | Compatible (uterus present) | | **Transverse vaginal septum** | Present (normal) | Yes — outflow obstruction | ✅ Compatible | | **Müllerian agenesis (MRKH)** | **Absent/rudimentary** | Yes — but uterus absent | ❌ **Contradicts normal ultrasound** | | **Cervical stenosis** | Present (normal) | Yes — outflow obstruction | ✅ Compatible | ### Why the Other Options Are Compatible - **Transverse vaginal septum**: Incomplete resorption of the urogenital sinus results in a membrane obstructing menstrual outflow. The uterus and ovaries are normal above the obstruction (Williams Gynecology). - **Cervical stenosis**: Congenital or acquired narrowing of the cervical canal obstructs outflow; uterus is present and normal on imaging. - **Asherman's syndrome**: While classically a cause of secondary amenorrhea, the question asks about recognized causes in the context of a normal uterus being present — the uterus is present in Asherman's, making it structurally compatible with the imaging finding, even if it is an atypical cause of primary amenorrhea. **High-Yield (Harrison's / Williams Obstetrics):** MRKH syndrome is the **most common cause of primary amenorrhea with normal secondary sexual characteristics**, but it is defined by **absence of the uterus** — a finding that directly contradicts the normal pelvic ultrasound in this stem. **Clinical Pearl:** When a primary amenorrhea question specifies a **normal uterus on ultrasound**, Müllerian agenesis is automatically excluded. The differential then shifts to outflow tract obstructions (vaginal septum, cervical stenosis, imperforate hymen) and intrauterine pathology (Asherman's).
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.