**Question:** Investigation of choice in a 55 years old post menopausal woman who has presented with postmenopausal bleeding:

A. Transvaginal ultrasound
B. Serum estradiol level
C. Hormone replacement therapy
D. Serum progesterone level

**Correct Answer:** A. Transvaginal ultrasound

**Core Concept:** Postmenopausal bleeding in a postmenopausal woman requires a comprehensive diagnostic workup to rule out underlying malignancies.

**Why the Correct Answer is Right:** In postmenopausal women with postmenopausal bleeding, a transvaginal ultrasound is the initial investigation of choice due to several reasons:

1. **Transvaginal ultrasound**: It allows for a detailed assessment of the endometrial thickness, morphology, and vascularity, which can provide significant insights into the nature of the endometrial changes. A thickened endometrium (> 4-5 mm), irregular endometrial morphology, or abnormal vascularity can suggest an underlying endometrial pathology such as endometrial hyperplasia or cancer.
2. **Safety and non-invasive nature**: Transvaginal ultrasound is a non-invasive procedure, which is crucial when considering the safety aspect in a vulnerable postmenopausal woman.
3. **Accuracy and cost-effectiveness**: Transvaginal ultrasound is a reliable and cost-effective screening tool that can help guide further management decisions.

**Why Each Wrong Option is Incorrect:**

**Option B (Serum estradiol level):**
Estradiol levels are useful in evaluating menopausal symptoms and assessing ovarian function, but they do not provide direct information regarding the endometrial pathology that leads to postmenopausal bleeding.

**Option C (Hormone replacement therapy):**
Hormone replacement therapy is a therapeutic approach for menopausal symptoms, not an investigation for postmenopausal bleeding.

**Option D (Serum progesterone level):**
Serum progesterone levels are essential in evaluating menopausal symptoms and reproductive function, but they do not directly provide information regarding the cause of postmenopausal bleeding.

**Option A (Transvaginal ultrasound):**
While transvaginal ultrasound is a valuable investigation in evaluating postmenopausal bleeding, it is not the only investigation. Other investigations may be required based on the ultrasound findings, such as endometrial biopsy or endometrial sampling (e.g., Pipelle or Pipelle endometrial sampling) if the ultrasound is suggestive of atypical endometrial pathology.

**Core Concept:** Transvaginal ultrasound is a valuable tool in evaluating postmenopausal bleeding and can guide further management decisions. However, additional investigations may be necessary in certain cases to confirm or rule out endometrial pathology.

**Clinical Pearls:**
1. **Transvaginal ultrasound**: It is the initial step in evaluating postmenopausal bleeding due to its non-invasive nature and ability to assess endometrial thickness, morphology, and blood flow to the uterus.