**Core Concept:** Post-menopausal bleeding is a common clinical presentation seen in women after menopause. It can be due to various causes including hormonal imbalances, uterine pathology, and endometrial hyperplasia/cancer. A thorough clinical examination, pap smear, and imaging studies help to narrow down the diagnosis.

**Why the Correct Answer is Right:** In this case, the patient presents with post-menopausal bleeding, and her pelvic examination and pap smear are unremarkable. The ultrasound reveals atrophic ovaries, which is a typical finding in post-menopausal women, and endometrial thickness of 1 mm, which is consistent with atrophic endometrium. The absence of other comorbidities further supports the diagnosis.

Given these findings, the most probable diagnosis is **Endometrial Atrophy**. This is a condition characterized by the thinning and atrophy of the endometrium due to the lack of estrogen stimulation during menopause. As a result, the endometrial thickness decreases, making it difficult to differentiate from post-menopausal bleeding caused by endometrial cancer.

**Why Each Wrong Option is Incorrect:**

A. **Endometrial Hyperplasia:** This condition involves the overgrowth of endometrial tissue, which is different from atrophy. The endometrial thickness would not be as low as in atrophic endometrium.

B. **Endometrial Cancer:** Although post-menopausal bleeding may be caused by endometrial cancer, the absence of other comorbidities and the endometrial thickness being 1 mm in this case makes cancer less likely compared to endometrial atrophy.

C. **Hormonal imbalance:** While hormonal imbalances can lead to post-menopausal bleeding, the patient's age and normal pap smear eliminate this as a primary cause in this case.

D. **Ovarian cyst:** As the patient is post-menopausal and has atrophic ovaries, ovarian cysts are less likely to be the cause of post-menopausal bleeding as compared to endometrial atrophy.

**Clinical Pearl:** In post-menopausal women, the most common cause of post-menopausal bleeding is endometrial atrophy due to the lack of estrogen stimulation. While other factors like hormonal imbalances, ovarian cysts, and endometrial cancer can be considered, the given clinical scenario favors endometrial atrophy due to the patient's age, normal pap smear, and normal-appearing ovaries on ultrasound.