(1)
Department of Fetal Medicine and Obstetric & Gynecological Ultrasound, Manipal Hospital, Bangalore, Karnataka, India
Endometrium is the mucous membrane that lines the inside of the uterus. It has a cell-rich connective tissue that surrounds the endometrial glands. It is composed of two layers: the superficial functional layer and the deeper basal layer. In each menstrual cycle, the superficial functional layer of the endometrium is shed and reconstituted from the underlying basal layer. Its thickness, morphology and vascularity change throughout the menstrual cycle in women of reproductive age.
4.1 Evaluation of Endometrium
The evaluation of the endometrium should be systematic, and reporting should be standardised. The IETA (International Endometrial Tumor Analysis group) statement is a consensus statement that has been published by a panel of experts (IETA consensus group) for terms, definitions and measurements for describing and reporting the endometrium and its pathologies.
The evaluation of the endometrium and uterine cavity can be done both by TAS and TVS. The TVS route is considered ideal for evaluating the endometrium. However, TAS may help, particularly in the presence of fibroids, an enlarged uterus or a mid-positioned (axially placed) uterus. Transrectal ultrasound scan should be considered if TVS is not possible due to any condition like vaginismus. It is best to do both a TAS and a TVS scan, because very often they complement each other.
The uterus is scanned (on 2D) in the sagittal plane from one cornu to the other and in the transverse plane from the cervix to the fundus. This gives us a good overall view of the uterus in the sagittal and transverse sections. 3D is useful for visualisation of the coronal section of the uterus which provides better information of the uterine cavity and EMJ (endomyometrial junction). Once the overview is done on ultrasound, the magnification should be increased focusing on the area of interest, i.e. the endometrium.
Generally the endometrium is easy to visualise. However, it may be difficult to study the endometrium in a mid-positioned uterus, because structures that lie perpendicular to the ultrasound beam are clearly visible but structures lying parallel to it are not. In such cases, one can place the probe in the anterior or posterior fornix and push on the cervix to retrovert or antevert the uterus further, to try and make the endometrium more perpendicular to the beam. TAS in such cases may provide better resolution. If visualisation is suboptimal, then that must be mentioned in the report. Saline or gel instillation (sonohysterogram) may help in better evaluation of the endometrium in cases where assessment is difficult or in those with an intracavitary pathology.
The endometrium is measured in a sagittal plane. The measurement is taken perpendicular to the endometrial midline, where the endometrium is thickest, excluding the hypoechoic adjoining myometrium. Two-layer thickness is measured and reported in millimetres (rounded off to 1 decimal point). If there is intracavitary fluid, then a single-layer thickness is measured where it is thickest, and it should be mentioned in the report that it is a single-layer thickness, or one can add the thickness of the endometrium of the opposite wall and report a two-layer thickness. When the endometrium cannot be visualised clearly, as is sometimes the case with a mid-positioned uterus, it should be reported as nonmeasurable.
When an intracavitary pathology is present, the total endometrial thickness including the lesion should be recorded. If an intracavitary myoma is clearly identified, then it should not be included in the measurement of endometrial thickness. Intracavitary lesions should be measured in millimetres in three perpendicular dimensions (as explained in Chap. 2). This helps calculate the volume of the lesion.
The amount of intracavitary fluid can be measured in three perpendicular dimensions to assess the volume. The IETA recommendation is that intracavitary fluid should be defined by its largest measurement in the sagittal plane.
Fig. 4.1
(a, b) Endometrium is measured in the midsagittal section of the uterus perpendicular to the endometrial midline, excluding the hypoechoic adjoining myometrium. The measurement is most accurate when the ultrasound beam is perpendicular to the endometrial stripe
Fig. 4.2
Measuring the endometrium in the presence of intracavitary fluid. (a) A single-layer thickness is measured and reported as such, or (b) one may measure the endometrial thickness of the opposite walls and add the two for reporting
Fig. 4.3
(a, b) In a mid-positioned uterus, the endometrium is difficult to measure and assess, as the ultrasound beam lies parallel to the endometrial stripe
Fig. 4.4
Intracavitary pathologies like polyps should be measured in three perpendicular dimensions so that their volume can be calculated. Arrow shows a hyperechoic line between the polyp and the endometrium
Fig. 4.5
Intracavitary fluid measured (a) in three perpendicular dimensions to obtain volume or (b) as the largest measurement in the sagittal plane (IETA recommendation)
This includes the assessment of the endometrial echogenicity, the endometrial midline and the endomyometrial junction (EMJ).
The echogenicity of the endometrium is compared with that of the myometrium. It could be hyperechoic, isoechoic or hypoechoic.
The endometrial echogenicity is considered uniform, if the endometrium is homogeneous with symmetrical anterior and posterior walls. The echogenicity is termed non-uniform, if the endometrium appears heterogeneous, asymmetrical or cystic.
The endometrial midline is the interface between the opposing surfaces of the two endometrial walls. It is defined as ‘linear’ if it is straight and hyperechogenic; ‘non-linear’ if it is waved and hyperechogenic; and ‘irregular’ or ‘not defined’ in the absence of any distinct midline echoes.
The EMJ is basically the outer margin of the endometrium. It could be described as regular, irregular, interrupted or not defined.
When an intracavitary lesion is present, a bright line is generally seen at the interface between the lesion and the endometrial walls, particularly if the lesion is smooth walled. If any lesion is seen within the cavity, its morphology should be described, i.e. its margins, echogenicity and vascularity.
Intracavitary lesions are better visualised in the presence of fluid in the endometrial cavity (including sonohysterogram). The lesion is defined as ‘extended’ if the endometrial abnormality involves 25 % or more of the endometrial surface, and as localised if less than 25 % of the endometrial surface is involved. Localised lesions are defined as ‘pedunculated’, if their maximum transverse diameter is less than the diameter of its base, and ‘sessile’ if their maximum transverse diameter is more than the diameter of its base.
In the presence of fluid in the endometrial cavity (including sonohysterogram), the endometrial outline (i.e. the endometrial surface facing the uterine cavity) is defined as ‘smooth’ if it appears regular; as having endometrial folds if there are multiple thickened ‘undulating’ areas with a regular profile; as ‘polypoid’ if there are deep indentations; or as ‘irregular’ if the surface is cauliflower-like or sharply toothed (‘spiky’).
Fig. 4.6
The endometrial midline: (a) linear, (b) non-linear, (c) not defined. The endometrium in (c) is hyperechoic and thick
Fig. 4.7
Endomyometrial junction 2D and 3D coronal view: (a) and (b) regular, (c) and (d) irregular, (e) and (f) not defined
Fig. 4.8
Endometrial outline: (a) regular, (b) polypoidal, (c) irregular
Doppler (Fig. 4.9)
For Doppler evaluation of the endometrium, the colour/power Doppler box should include the endometrium with the surrounding myometrium. Magnification is important and the Doppler setting should be optimised to ensure maximal sensitivity for blood flow (details in the section on Doppler in Chap. 2).
Vascularity is assessed subjectively by the use of colour score from 1 to 4, 1 being no colour and 4 being maximal colour (details in the section on Doppler in Chap. 2). Spectral wave forms can also be used to measure RI and PI of lesions in some cases.
The vascular pattern in the endometrium is reported with respect to the presence or absence of ‘dominant’ vessels. A ‘dominant’ vessel is defined as a distinct vessel crossing the EMJ. This may show branching within the endometrium. ‘Dominant’ vessels could be a single vessel (feeder vessel or pedicle artery sign) or could be multiple having either a ‘focal origin’ at the EMJ or a ‘multifocal origin’. Other vascular patterns include scattered vessels in the endometrium, without origin at EMJ and circular flow (e.g., submucous fibroid).
Fig. 4.9
Vascular pattern in endometrium. (a) Dominant single vessel with origin at EMJ – endometrial polyp. (b) Multiple vessels with focal origin at EMJ – focal endometrial carcinoma. (c) Multifocal origin at EMJ – endometrial hyperplasia. (d) Scattered vessels without origin at EMJ – invasive endometrial carcinoma. (e) Multifocal origin at EMJ – normal secretory endometrium (note the similarity in pattern with endometrial hyperplasia in (c)). (f) Same case as (e) flow with 3D glass body display, showing arcuate vessels, radial vessels (short arrow) and spiral arteries (long arrow) in a normal secretory endometrium
4.2 Normal Endometrium
Endometrial thickness, morphology and vascularity change throughout the menstrual cycle in women in the reproductive age group. In addition, the endometrium appears different in women prior to menarche and after menopause.
Most often the endometrial types seen and reported on ultrasound are menstruating, proliferative, early secretory, secretory and hyperechoic.
4.2.1 Endometrium in Paediatric Age Group (Fig. 4.10)
The endometrium appears as a thin echogenic line, and a small percentage of neonates have minimal fluid collection within the endometrial cavity. At the onset of puberty, the endometrium gradually increases in thickness and becomes like that of an adult.
Fig. 4.10
Thin echogenic endometrium measuring 1 mm, in a premenarchal girl
4.2.2 Endometrium in Reproductive Age Group (Figs. 4.11 and 4.12)
Endometrial changes during the menstrual cycle, parallel cyclical ovarian changes.
Menstrual phase (Day 1–6 of menstrual cycle*):
During menstruation, the endometrium appears hyperechoic and complex. By the end of menstruation, the endometrium is thin, about 1–4 mm in thickness. Baseline scans in women on the treatment for infertility are done on Day 2 or 3 of the menstrual cycle. No subendometrial flow is seen at this time.
Proliferative phase or follicular phase (Day 6–14 of menstrual cycle*):
The endometrium gradually increases in thickness from 5 mm to about 10–12 mm. At the time of administrating the hCG injection in women undergoing follicular imaging for infertility, the endometrial thickness should be at least 6 mm, and the results are best when the thickness is 8 mm. The proliferative phase endometrium is typically seen as a three-layer endometrium with an echogenic basal layer, a hypoechoic inner functional layer and an echogenic midline at the interphase of the two layers. Minimal intracavitary fluid may be seen in the preovulatory phase. The vascularity of the endometrium gradually increases to a maximum, just prior to ovulation.
Secretory phase or luteal phase (Day 14–28 of menstrual cycle*):
The endometrial thickness may decrease minimally at ovulation, but after that it increases gradually in thickness (7–15 mm). The endometrium also becomes hyperechoic starting from the periphery towards the centre. This increased echogenicity is believed to be due to stromal oedema and the presence of mucus and glycogen in the glands. This stromal oedema is also responsible for the increased echogenicity of the myometrium beyond it due to acoustic enhancement.
Endometrium in the Post-partum Period
The endometrium following delivery is less than 2 cm. Some amount of fluid, blood products and echogenic debris, including a small amount of gas, are normal in the first week after delivery and may be seen up to 3 weeks post-partum.
Fig. 4.11
Endometrium in different phases of menstrual cycle. (a) Menstruating endometrium, (b) proliferative endometrium, (c) early secretory endometrium, (d) secretory endometrium
Fig. 4.12
Normal post-partum endometrium. (a) Post-partum second week – fluid, debris and minimal gas shadows seen in the endometrial cavity. Single-layer thickness of the endometrium was 4.4 mm. (b, c) Uterus – on post-partum Day 18 with (b) single-layer endometrial thickness of 3.5 mm. This can be wrongly interpreted as being much thicker (marked in the image) because of isoechoic endometrium and prominent arcuate vessels wrongly interpreted as the EMJ. (c) Arcuate vessels seen on Doppler
4.2.3 Endometrium in Postmenopausal Women (Fig. 4.13)
The normal postmenopausal endometrium is thin, homogeneous and echogenic. In postmenopausal women, simple measurement of the endometrial thickness is useful in assessing the risk for endometrial cancer (unlike in premenopausal women). An endometrial thickness of 4 mm or less decreases the likelihood for endometrial cancer by a factor of 10, in a postmenopausal woman.
Fig. 4.13
Thin echogenic endometrium measuring 2 mm, in a postmenopausal lady
4.3 Endometrial Polyps
Endometrial polyps are frequently diagnosed in both symptomatic and asymptomatic women. They are growths arising from the endometrial lining of the uterus and may be associated with hyperplasia. Though most are benign, some may show malignancy within.
Polyps could cause intermenstrual spotting and infertility/subfertility. Polyps that cause abnormal uterine bleeding are more likely to be polyps with atypical hyperplasia.
Ultrasound Features of Endometrial Polyps (Figs. 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 4.21, 4.22, 4.23, 4.24, 4.25, 4.26, 4.27, 4.28, 4.29, 4.30 and 4.31)
A polyp typically appears as a circumscribed hyperechoic area within the endometrial cavity and, therefore, is better seen in a proliferative endometrium. The polyp is measured in three perpendicular dimensions.
Very often, a fine hyperechoic line is seen around the polyp along the interphase between the polyp and the surrounding endometrium (similar to the central line in a proliferative endometrium). This hyperechoic line is seen to be discontinuous at the site of entry of the feeder vessel into the polyp. The presence of this hyperechoic line often helps in delineating a polyp on 2D, in a hyperechoic or secretory endometrium.
Sometimes these polyps show tiny cystic spaces within. The cystic spaces relate to dilated endometrial glands within the polyp. In postmenopausal women with a thick endometrium, a focal area with small cystic areas within should raise the possibility of an endometrial polyp. Polyps in patients on tamoxifen also show cystic spaces.
At times they are fleshy and large, and these could be adenomyomatous polyps.
On Doppler, a dominant vessel (‘feeder vessel’/‘pedicle artery sign’) is seen approaching the polyp from the adjoining myometrium across the EMJ. This vessel may show branching within the polyp. This feeder vessel is very helpful in making a diagnosis of polyps and also in identifying the site of origin of the polyp within the endometrial cavity. The average RI for feeder vessels of polyps is about 0.6.
One may not see the feeder vessel of a polyp. This could happen if the Doppler settings are not proper or the direction of flow in the vessel is perpendicular to the ultrasound beam. In the latter case, angulating the probe could help. Sometimes the vessel is better seen on TAS than TVS because the direction of flow on TVS may be perpendicular, but on TAS it may be parallel, enabling visualisation of the vessel.
These polyps are often visualised well on 3D rendered coronal images of the uterine cavity.
Polyps could be multiple, each with its individual feeder vessel.
Some of these polyps may have a long pedicle, and though they may originate higher up, they may be seen much lower down, often in the cervical canal.
When there is fluid in the endometrial cavity, either blood or at sonohysterogram, polyps are well visualised. They are seen as echogenic, smooth-surfaced, intracavitary masses. Their site of origin is also well seen. The polyp may be broad based or sessile.
Sometimes, one is able to see the rounded, blunt lower margins of a polyp in the endometrial cavity, especially if there is some minimal fluid below it, which helps in differentiating it from a thickened endometrium.
Some polyps show hyperplastic endometrium, and in rare cases they could be malignant. One must consider the possibility of malignancy in a polyp especially if they are fleshy and heterogeneous, and a Doppler study of the feeder vessel shows a low RI of 0.42 or below.
Sometimes clots within the endometrial cavity can mimic a polyp. However, neither feeder vessel nor flow will be seen in these clots. One must be aware of the artefact caused by menstrual flow of blood in the endometrial cavity. This could even produce a tracing like that of a venous flow on pulse wave Doppler. However, no arterial flow will ever be seen in the case of a clot. In addition, menstrual flow is seen along the periphery of clots, unlike polyps where vascular flow is seen within the tissue of the polyp. Also, if one applies pressure with the probe, in cases with menstrual flow artefacts, a reversal of flow direction may be noticed (blue to red or vice versa).
In cases with clots appearing like polyps, the clots may be dislodged or missing either when a repeat scan is done after the patient has been asked to strain or if the scan is repeated after a day or two.
As mentioned earlier, the best time to evaluate the endometrium for polyps is the proliferative phase (Day 9–12 of menstrual cycle). The polyp stands out clearly in the triple line pattern of the proliferative endometrium. In all other types of endometrium, a polyp may not be clearly seen since it is isoechoic with the rest of the endometrium. In such cases, the hyperechoic line around the polyp and the feeder vessel may help in diagnosis.
A thick endometrium diagnosed on greyscale ultrasound sometimes turns out to be a polyp on Doppler (on visualisation of the feeder vessel) or at surgery
A mid-positioned uterus often results in suboptimal evaluation of the endometrium on TVS, and therefore a polyp can be missed. In some of these cases, it may be better visualised on TAS instead.
Polyps, particularly small ones, can be left unattended unless they are symptomatic. Hysteroscopy is the method of choice for management. It is important to note that often a polyp presenting as a thickened endometrium is missed on regular D&C, and there is scanty endometrium on curettage. This is because the curette has missed the polyp and gone around it curetting the surrounding thin endometrium. The referring gynecologist is surprised that the ultrasound report mentioned a thick endometrium and there were hardly any curettings!
Fig. 4.14
Hyperechoic small polyp in a proliferative endometrium
Fig. 4.15
Hyperechoic polyp clearly visualised in a proliferative endometrium. The hyperechoic line surrounding the polyp is discontinuous at the site of entry of the feeder vessel (arrow) which is seen on (a) greyscale and (b) Doppler
Fig. 4.16
Polyp in a secretory endometrium. Hyperechoic line (arrows) between polyp and endometrium helps delineate and diagnose the polyp (a) on 2D greyscale and (b) on 3D
Fig. 4.17
(a, b) 67-year-old postmenopausal lady with an endometrial thickness of 17.8 mm. (a) Polyp with tiny cystic spaces. (b) Feeder vessels supplying the polyp, (c, d) 70-year-old postmenopausal lady with ET of 26 mm. (c) TAS – a, single prominent feeder vessel crossing the EMJ and branching within the thickened endometrium raises a high possibility of an endometrial polyp; (d) TVS – flow seen in the endometrium in more than one vessel (PRF 0.3), but despite repeated attempts, the origin of flow across the EMJ is not seen. With TVS alone, it was not possible to see the feeder vessel from the EMJ probably because it is perpendicular to the ultrasound beam at its origin. To improve accuracy of diagnosis, doing both TAS and TVS routinely is therefore ideal
Fig. 4.18
Patient on tamoxifen for carcinoma breast. (a) Shows a polyp and cystic spaces (small white arrows) in the endometrium. (b) Shows the feeder vessel of the polyp
Fig. 4.19
Adenomyomatous polyp. (a) Seen on greyscale. (b) Showing Doppler flow. (c) Seen at hysteroscopy
Fig. 4.20
Pedicle artery sign: A dominant feeder vessel is seen approaching the polyp across the EMJ
Fig. 4.21
(a) Thickened isoechoic endometrium with a hyperechoic line (arrow) raising a suspicion of a polyp. (b) A single feeder vessel with branching, suggestive of an endometrial polyp. (c) Glass body rendering of the polyp with feeder vessel. Branching of the feeder vessel within the polyp is well seen. (d) Spectral Doppler flow of feeder vessel. HPE: polyp with complex hyperplasia without atypia
Fig. 4.22
Endometrial polyp well seen on 3D rendered coronal image view of the endometrial cavity. In this case, there was minimal fluid in the endometrial cavity, and therefore the polyp is well delineated
Fig. 4.23
Two endometrial polyps showing cystic spaces seen distinctly. (a) A narrow anechoic wedge seen between the two (arrow) on greyscale. (b) Each polyp has its own feeder vessel arising from the anterior uterine wall. (c) 3D rendered image showing the two polyps
Fig. 4.24
Endometrial polyp seen arising from the upper corpus of the uterus and presenting as a fleshy, large (42.7 cm3) polyp with multiple cystic spaces protruding out of the cervix . The external os diameter was 1.8 cm. Polyp seen (a) on greyscale and (b) on Doppler. (c) Lower margins of the polyp are well seen on GSV. (d) The polyp shows high vascularity with low resistance flows. One of the causes for such flows (high colour score and low RI) can be superadded infection. HPE: endometrial polyp with cystic hyperplasia
Fig. 4.25
Blood in the endometrial cavity enhancing delineation of two endometrial polyps (a) on 2D with Doppler and (b) on 3D
Fig. 4.26
(a) Hyperechoic, 4.4 cm long polyp seen filling the endometrial cavity. (b) Lower rounded end of polyp (arrow) is visualised which helps in differentiating it from other causes of thickened endometrium. (c) The feeder vessel of the polyp is seen approaching it from the anterior wall of the uterus. HPE: simple hyperplasia
Fig. 4.27
Large, fleshy polyp with a thick feeder vessel showing low RI. HPE: endometrioid adenocarcinoma arising in an adenomyomatous polyp
Fig. 4.28
(a) Hyperechoic clot filling the endometrial cavity in a menstruating patient complaining of menorrhagia, which can raise a suspicion of a fleshy endometrial polyp. (b) Flow seen on colour Doppler is the menstrual flow. This raises a false suspicion of flow within an endometrial polyp. (c) Empty uterine cavity noted the next day, confirming the diagnosis of a clot in the endometrial cavity the previous day
Fig. 4.29
Thickened endometrium with hyperechoic scattered foci within. (a) TAS – shows feeder vessel. (b) TVS – shows the rounded lower end of polyp. HPE: adenomyomatous polyp
Fig. 4.30
Hypoechoic polyp with a feeder vessel approaching it from the uterine fundus on (a) Doppler and (b) 3D with glass body rendering
Fig. 4.31
(a) Polyp with cystic hyperplasia. (b, c) Feeder vessel is difficult to trace. This happens in polyps that are primarily cystic with minimal stroma
Summary: Endometrial Polyps
Endometrial polyps are commonly seen in both symptomatic and asymptomatic women. They may present with intermenstrual spotting or subfertility.
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