Introduction

Endometrial polyps are benign tumors within the endometrial mucosa consisting of a stromal axis surrounded by cylindrical epithelium containing variable quantities of glands and blood vessels. Although they may be found as an incidental finding, endometrial polyps are often associated with clinical symptoms such as abnormal vaginal bleeding and infertility .

Endometrial polyps can appear as a single or multiple growths, sessile or pedunculate, and of variable dimensions and color according to the degree of vascularization. The reported prevalence of endometrial polyps widely varies and ranges from 7.8% to 34.9%, depending upon the definition of a polyp, diagnostic method used, the population studied, and it appears to increase with age .

Classification

From the histological viewpoint, the following types of endometrial polyps can be distinguished:

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  Hyperplastic polyps . Arising from the basal endometrial layer, which is sensitive to estrogen, they are the result of the estrogen stimulation not balanced by the effect of progestin. They can be associated with diffuse endometrial hyperplasia (EH) and can have fewer localized atypical areas, particularly in postmenopausal age.

  
  
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  Atrophic polyps . Typical of postmenopausal age, they are generally regressive alterations of functional or hyperplastic polyps.

  
  
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  Functional polyps . They show glandular alterations similar to those of the surrounding endometrium, as they respond to the hormonal stimuli of the menstrual cycle.

  
  
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  Adenomyomatous polyps . They are characterized by varying amounts of smooth muscle cells and fibrous tissue. The “atypical” forms are characterized by the concomitant presence of benign endometrial glands and stroma with structural atypia consisting mainly of smooth muscle, and in which the likelihood of association with endometrial cancer transformation is about 9%.

  
  
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  Pseudopolyps . Small sessile lesions whose structure is identical to the surrounding endometrium; they are detected only in the secretory phase of the menstrual cycle, and then disappear with the menstrual flow.

Classification

From the histological viewpoint, the following types of endometrial polyps can be distinguished:

• –
  

  Hyperplastic polyps . Arising from the basal endometrial layer, which is sensitive to estrogen, they are the result of the estrogen stimulation not balanced by the effect of progestin. They can be associated with diffuse endometrial hyperplasia (EH) and can have fewer localized atypical areas, particularly in postmenopausal age.

  
  
• –
  

  Atrophic polyps . Typical of postmenopausal age, they are generally regressive alterations of functional or hyperplastic polyps.

  
  
• –
  

  Functional polyps . They show glandular alterations similar to those of the surrounding endometrium, as they respond to the hormonal stimuli of the menstrual cycle.

  
  
• –
  

  Adenomyomatous polyps . They are characterized by varying amounts of smooth muscle cells and fibrous tissue. The “atypical” forms are characterized by the concomitant presence of benign endometrial glands and stroma with structural atypia consisting mainly of smooth muscle, and in which the likelihood of association with endometrial cancer transformation is about 9%.

  
  
• –
  

  Pseudopolyps . Small sessile lesions whose structure is identical to the surrounding endometrium; they are detected only in the secretory phase of the menstrual cycle, and then disappear with the menstrual flow.

Etiopathogenesis

The exact cause of polyps is unknown, probably due to many causative factors. Numerous hypotheses for the onset of endometrial polyps have been suggested and they include the following:

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  Genetic and familial hereditary factors : clusters of anomalies in chromosomes 6 and 12 that may alter the proliferative process, resulting in endometrial overgrowth and polyp formation . Indeed, familial adenomatous polyposis, diabetes, and hypertension may have a role.

  
  
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  Inflammatory factors : women with polyps demonstrate alterations in endometrial levels of matrix metalloproteinases and cytokines compared with control subjects; these changes could produce the pathologic processes or they could be the result of the pathology development .

  
  
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  Endocrine factors : main example is a condition of imbalanced hyperestrogenism (obesity, polycystic ovary syndrome, late menopause, estrogen secreting gonadal stromal tumors, and chronic liver disease) .

  
  
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  Iatrogenic factors : as unbalanced estrogen therapy (toremifene or tamoxifen therapy for breast cancer).

Clinical appearance

Although endometrial polyps may be totally asymptomatic, frequently, they are found to be associated with one or many symptoms, as follows:

• 1.
  

  Abnormal Uterine Bleeding (AUB) : It is the most common presenting symptom for endometrial polyp both premenopausal and postmenopausal age, occurring in approximately 68% of cases . However, it may present as intermenstrual spotting and/or postcoital spotting (particularly in cases of coexisting cervical polyps).

  
  
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  The presence of endometrial polyps in a significant proportion of patients with AUB is because of the patient’s hyperestrogenic state at the onset of symptoms, and is not itself a direct cause of these symptoms. Instead, endometrial polyps may directly account for bleeding, particularly where their mass and/or number occupy much of the volume of the uterine cavity, causing an ulceration of the endometrium.

  
  
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  In postmenopausal patients, AUB can be highly variable related to the number, size, and vascularity of the lesions, and is usually associated with an increased risk of malignancy in a polypoid lesion.

  
  
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  Infertility : Endometrial polyps are found in 15–25% of infertile women, although the causal relationship remains uncertain . There are underlying etiological patterns that might have an adverse impact on female fertility, and most of them are still being studied. Hypotheses include mechanical obstruction hindering ostium function and affecting sperm migration and biochemical effects of polyps on implantation or embryo development . Women treated with gonadotropins for infertility are exposed to a higher level of estrogens, which predispose them to the development of endometrial polyps . Numerous studies have shown an increased pregnancy rate secondary to a polypectomy (15–24%). However, the lack of randomized trials does not allow for a definitive conclusion on the potential role of polypectomies in increasing pregnancy rates.

  
  
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  Rare symptoms : Pain of variable intensity, related to reflex contractions of the uterus, can rarely occur; the contractions can displace the lesion progressively toward the cervix and can cause, in some instances, its complete expulsion. Large polyps can also present with necrosis, which can result in a vaginal serosanguinous discharge having an unpleasant odor.

Malignant transformation

Most endometrial polyps are benign; however, they may become hyperplastic, with malignant transformation developing in 0–12.9% of polyps in case series reported to date . The risk of malignancy associated with endometrial polyps is highest in postmenopausal symptomatic women. The reported incidence of carcinoma confined to endometrial polyps varies from 0% to 4.8%. The risk of malignancy in premenopausal women has been significantly correlated with increasing age and menopausal status, polyps with a size >1.5 cm, hypertension, and tamoxifen use . Ultrasonography may aid in the diagnosis of neoplastic change within endometrial polyps: the variation in range is dependent on the endometrial thickness used as the requirement for further investigation by more invasive methods .

Diagnosis

Transvaginal sonography

An endometrial polyp appears in two-thirds of cases with a focal, hyperechoic, and well-defined thickening of the endometrium, at times associated with multiple areas of hypoechogenicity. Occasionally, the polyp may appear delineated by a thin hypoechoic stripe.

The polyp may also appear as a no-specific endometrial thickening or focal mass within the endometrial cavity: such sonographic findings are not specific to polyps, and other endometrial abnormalities such as submucosal fibroids may have the same features ( Fig. 1 ).

2D transvaginal ultrasound: the sagittal view allows to identify a profile showing an endometrial trilinear pattern (periovulatory) interrupted by a focal thickening, oval, of about 13.7 × 5.8 mm, suggestive of an endometrial polyp.

Transvaginal sonography (TVS) is best performed in premenopausal women before 10th day of the cycle, when the endometrium is at its thinnest, to minimize the risk of false-positive and false-negative findings . Indeed, Doppler fluximetry, especially at childbearing age, is often capable of identifying the vascular axis of the polyp. Finally, 3D US is an innovative imaging technique with the ability to generate multiplanar reconstructed images through the uterus and its external contours. The coronal view is the most useful scan plan, allowing more accurate visualization between the endometrium and myometrium at the fundus and cornual angles ( Fig. 2 ).

On 2D imaging (left), the hyperechoic endometrial area (arrow) suspect for polyp is shown. On 3D reconstruction of the coronal plane, the size of the polyp (arrow) and its location in the uterine cavity are demonstrated.