Primary Amenorrhea with Normal Secondary Sexual Characteristics
The most likely diagnosis is testicular feminization (androgen insensitivity syndrome), option C. 1, 2
Clinical Reasoning
This 17-year-old presents with the classic triad that points to androgen insensitivity syndrome:
- Primary amenorrhea (never had menses) 2
- Normal breast development (Tanner stage V) indicating adequate estrogen 1, 2
- Normal pubic hair development (Tanner stage V) 1
Why Testicular Feminization (Androgen Insensitivity Syndrome)?
In complete androgen insensitivity syndrome (CAIS), patients have:
- 46,XY karyotype with functioning testes that produce testosterone, which is aromatized to estrogen, explaining the normal breast development 1, 2
- Absent or blind-ending vagina and absent uterus due to anti-Müllerian hormone from testes, causing primary amenorrhea 1, 3
- Normal female external genitalia and breast development from peripheral estrogen conversion 1, 2
- Pubic and axillary hair that may be present (though sometimes sparse) from adrenal androgens 1
The key distinguishing feature is normal secondary sexual characteristics with primary amenorrhea, which indicates adequate estrogen production but absent uterus. 1, 2
Why Not the Other Options?
Hypogonadotropic Hypogonadism (Option A)
- Would present with absent or incomplete breast development due to low estrogen 4, 5
- This patient has Tanner stage V breast development, ruling this out 1, 2
Transverse Vaginal Septum (Option B)
- Would present with cyclic pelvic pain from obstructed menstrual flow (cryptomenorrhea) 1
- Patient has no symptoms of obstruction and likely has absent uterus on examination 1
- This is the most common cause when uterus is present, but clinical picture suggests absent uterus 1
Gonadal Agenesis (Option D)
- Would result in hypergonadotropic hypogonadism with absent or poor breast development 5, 2
- Patient's normal breast development indicates functioning gonads producing estrogen 1, 2
Diagnostic Confirmation
The workup should include:
- Pelvic ultrasound or MRI to confirm absent uterus and identify gonads 5, 3, 2
- Karyotype analysis to confirm 46,XY 1, 2
- Testosterone levels (typically in male range) and FSH/LH (normal to low-normal) 2
Critical Management Considerations
- Gonadectomy is recommended after completion of puberty due to 25-30% risk of malignancy in undescended testes 2
- Estrogen replacement therapy after gonadectomy to prevent osteoporosis and maintain bone health 4, 5
- Psychological counseling and support regarding diagnosis, fertility implications, and gender identity 2
- Vaginal dilation therapy may be needed for sexual function 2