Answer:
The trans-vaginal US examination does not reveal any polyp in this patient with post menopausal bleeding. The endometrium (E) is thickened. The HSG demonstrates the polyp (P) in the endometrial cavity

Discussion:
Hysterosonography
Hysterosonography is superior to endovaginal US in the evaluation of the endometrial thickness in patients with post-menopausal bleeding. By hysterosonography one can differentiate sub-endometrial lesions from endometrial lesions. It is an excellent procedure to demonstrate changes related to tamoxifen therapy on the endometrium.
Women with postmenopausal vaginal bleeding are diagnosed by HSG to have polyps and sub-endometrial fibroids. A small percentage of women are diagnosed with endometrial cancer. An endometrial thickness of 4 or 5 mm or less almost completely excludes endometrial carcinoma. HSG has been shown to be useful for evaluating the endometrium, particularly in patients with PMB. Even when the endometrial thickness is 5 mm or less, HSG is accurate in identifying an anatomic cause of the bleeding in some cases.

Endometrial Polyps
In the general population, endometrial polyps are composed of three components: (a) stroma of dense fibrous tissue, (b) thick-walled vascular channels, and (c) endometrial glands. The incidence of endometrial polyps is higher in women treated with tamoxifen than in untreated women: 8%–36% versus 0%–10%. Although these polyps may cause abnormal uterine bleeding, most women are asymptomatic.
"Tamoxifen" induced polyps are larger and are differentiated from the ordinary type by the proliferative process seen as cystic glandular dilatation, and aberrant epithelial differentiation or metaplasia. If periglandular stromal condensation seen, it may be a form of müllerian adenosarcoma. Extensive stromal fibrosis within the polyp may make resection difficult at hysteroscopy.