Why do uterine polyps form

Overview

Uterine polyps, also called endometrial polyps, are growths that develop from the inner lining of the uterus (endometrium). These finger-like projections extend into the uterine cavity and vary in size from a few millimeters to several centimeters. First systematically described in medical literature in the 19th century, their clinical significance became clearer with the development of hysteroscopy in the 1970s, which allowed direct visualization. The prevalence increases with age, particularly during perimenopause (ages 40-50), though they can occur at any reproductive age. Historically considered mostly benign, modern studies since the 1990s have revealed their association with abnormal uterine bleeding in 25-30% of cases and their potential for malignant transformation. Diagnostic advances including transvaginal ultrasound (developed in the 1980s) and saline infusion sonohysterography (1990s) have improved detection rates from approximately 70% to over 90% in contemporary practice.

How It Works

Uterine polyps form through localized hyperplasia of endometrial tissue, where glandular and stromal components proliferate abnormally. The primary mechanism involves hormonal influences, particularly estrogen stimulation without adequate progesterone opposition. Estrogen promotes endometrial cell growth and proliferation, while progesterone typically inhibits growth and promotes differentiation. When this balance is disrupted—such as during perimenopause when ovulation becomes irregular—focal areas of endometrium may continue growing unchecked. At the cellular level, polyps develop from the basal layer of the endometrium and contain fibrous stroma, thick-walled blood vessels, and endometrial glands. They often have a stalk (pedunculated) but can be broad-based (sessile). The vascular supply comes from a single feeding vessel, making them prone to bleeding. Genetic factors also contribute, with studies showing monoclonal origin in many polyps and associations with chromosomal rearrangements. Additional mechanisms include local growth factor imbalances (particularly involving insulin-like growth factors) and inflammatory mediators that stimulate angiogenesis and tissue proliferation.

Why It Matters

Uterine polyps matter clinically because they represent the most common intracavitary uterine abnormality, accounting for approximately 25% of abnormal uterine bleeding cases in premenopausal women and up to 33% in postmenopausal women. Their significance extends beyond bleeding symptoms to fertility implications—polyps are found in 15-25% of infertile women and their removal improves pregnancy rates by 40-80% in some studies. For postmenopausal women, polyps carry particular importance as they may harbor malignancy in 1.5-4.8% of cases, necessitating careful evaluation. The economic impact is substantial, with diagnostic and treatment costs for symptomatic polyps estimated in the thousands per case in healthcare systems. Furthermore, polyps serve as markers for endometrial health, with their presence sometimes indicating underlying hormonal imbalances or increased cancer risk that requires broader medical management beyond simple removal.