Endometrial polyp

Endometrial polyps are benign nodular protrusions of the endometrial surface, and one of the entities included in a differential of endometrial thickening. Endometrial polyps can either be sessile or pedunculated. They can often be suggested on ultrasound or MRI studies but may require sonohysterography or direct visualization for confirmation.

Epidemiology

The prevalence of endometrial polyps increases with age and ranges from 8-35% ⁸. Endometrial polyps are frequently seen in patients receiving tamoxifen. Other risk factors include foreign bodies, multiparity, chronic cervicitis and estrogen secretion.

Clinical presentation

Most polyps are asymptomatic although they can be a common cause of postmenopausal bleeding (can account for ~30% of cases ⁵). In premenopausal women, they may cause intermenstrual bleeding, metrorrhagia, and infertility.

Pathology

Polyps can be histologically characterized as localized hyperplastic overgrowths of glands and stroma. They consist of irregularly-distributed endometrial glands and stroma and generally consist of three components: 

• a stroma of focally or diffusely dense fibrous or smooth muscle tissue

• thick-walled vessels

• endometrial glands 

~2.5% (range 0.8-4.8%) of endometrial polyps are premalignant or malignant ⁹.

An adenomyomatous endometrial polyp is a pedunculated variant comprising of smooth muscle tissue in addition to the usual endometrial glands and stroma.

Location

• there is a predilection towards the fundal and cornual regions within the uterus

• they can be multiple in ~20% of cases

• rarely protrude into the endocervical canal or through the cervical os

Radiographic features

Hysterosalpingography (HSG)

Polyps may be seen as pedunculated or sessile filling defects within the uterine cavity. This is not a preferred method for evaluation compared with the other modalities.

Ultrasound

The best time of examination for endometrial polyp is postmenstrual. 

• ​usually solitary homogeneous and echogenic lesion

• interrupted mucosa sign ¹⁰: the endometrial polyp focally interrupts the normal mucosal contour of the uterine cavity

• it is rarely hypoechoic or heterogeneous

• a stalk to the polyp may either be thin (i.e. pedunculated) or broad-based

• the bright edge sign ¹¹: the appearance of one or two well-defined short echogenic linear echoes at the polyp borders which are perpendicular to the ultrasound beam

• may appear isoechoic as a focal non-specific thickened endometrium, without visualization of a discrete mass

• can rarely appear as diffuse endometrial thickening as the endometrial polyp fills the endometrial cavity, mimicking endometrial hyperplasia

• rarely cystic spaces could be seen corresponding to dilated glands filled with proteinaceous fluid within the polyp ³

• may be surrounded by endometrial fluid

Color Doppler

• feeding artery sign: a single feeding vessel may be seen extending to the polyp on color Doppler imaging ⁷

  • visualization of a vascular pedicle is 76% sensitive and 95% specific for endometrial polyps ⁷

3D ultrasound

• 3D ultrasound may be useful to help delineate the borders of a polyp

Sonohysterography 

Although not always necessary for a diagnosis, polyps are well-characterized on sonohysterography and appear as echogenic, smooth, intracavitary masses outlined by the fluid. The typical appearance of an endometrial polyp at sonohysterography is a well-defined, homogeneous, polypoid lesion that is isoechoic to the endometrium with preservation of the endometrial-myometrial interface ⁵. There is usually a well-defined vascular pedicle within the stalk.

MRI

Signal characteristics include:

• T1: often isointense signal to endometrium

• T2: endometrial polyps are often seen as hypointense intracavitary masses surrounded by hyperintense fluid and endometrium

• T1 C+ (Gd): can show either homogeneous or heterogeneous enhancement

Treatment and prognosis

Most polyps are benign and may be treated with a polypectomy, if symptomatic.

Complications

• prolapse: prolapsed endometrial polyp

• a very small percentage (0.5-3%) of polyps may contain endometrial carcinoma ⁴

Differential diagnosis

Entities that can potentially mimic an endometrial polyp include:

• uterine leiomyoma: especially if submucosal and pedunculated, although most leiomyomas tend to be hypoechoic on ultrasound and demonstrate hypointense signal on MRI

• foci of endometrial hyperplasia

• endometrial carcinoma

• intrauterine blood clot

For hyperechoic content within the endometrium also consider:

• intrauterine blood clot

• retained products of conception

See also

• cervical polyp

• tubal polyp