A girl has primary amenorrhea with normal ovaries, absent internal genitalia but normal external genitalia. Most probable diagnosis?:
**Core Concept**
The girl's presentation of primary amenorrhea, normal ovaries, absent internal genitalia, and normal external genitalia points towards a developmental issue related to the formation of the Müllerian ducts, which give rise to the internal female reproductive organs.
**Why the Correct Answer is Right**
The most probable diagnosis is Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, a congenital anomaly characterized by the absence or underdevelopment of the vagina and uterus in individuals with normal ovaries and external genitalia. This condition is caused by a mutation in the WNT4 gene, which is essential for the proper development of the Müllerian ducts. The absence of the uterus and vagina leads to primary amenorrhea, while the presence of normal ovaries ensures that the external genitalia and secondary sexual characteristics develop normally.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the girl's presentation. While some individuals with Androgen Insensitivity Syndrome (AIS) may have normal external genitalia, they typically have male internal genitalia and are resistant to androgens.
* **Option B:** This option is incorrect because it does not account for the girl's normal ovaries and external genitalia. Turner Syndrome is characterized by ovarian dysgenesis and short stature, which are not present in this case.
* **Option C:** This option is incorrect because it does not accurately describe the girl's presentation. While some individuals with congenital adrenal hyperplasia (CAH) may have ambiguous genitalia, they typically have normal ovaries and do not present with primary amenorrhea.
**Clinical Pearl / High-Yield Fact**
Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is a common cause of primary amenorrhea in individuals with normal ovaries and external genitalia. It is essential to differentiate MRKH syndrome from other causes of primary amenorrhea, such as Turner Syndrome and Androgen Insensitivity Syndrome, which have distinct clinical and genetic features.
**Correct Answer:** C.