Ultrasound signs of a normal uterus

Echographic characteristics of the normal anatomical structure of the uterus

Ultrasound is begun by studying the location of the uterus, which is of great importance in carrying out invasive procedures.

The position of the uterus. With transabdominal ultrasound, longitudinal scanning can diagnose the displacement of the uterus along the sagittal axis based on the angle of inclination between the body and the cervix: with hyperanteflexion, the angle decreases, with retroflection, the magnitude of this angle with respect to the bladder exceeds 180 °. A study in the cross section allows one to identify the deviation of the uterus to the left or to the right.

With transvaginal ultrasound scanning, the definition of the uterine topography presents certain difficulties, which is associated with a decrease in the area of the projection of ultrasonic waves. Consequently, depending on the position of the uterus in the cavity of the small pelvis, various departments of the pelvis are sequentially examined; detection of the uterine fundus testifies to the retroflexion of the uterus, the cervix uteri - to anteflexia.

In the anteroposterior section with transvaginal ultrasound, the condition of the cervix is determined: the direction of the axis of the cervical canal, the state of the endocervix and the internal pharynx.

The cervical canal is very easily visualized and defined as an extension of the endometrium. Endocervix is represented on the echogram with a linear echo with a high level of sound absorption. The ultrasound picture depends on the quantity and quality of cervical mucus and varies depending on the phase of the menstrual cycle: from a thin echogenic structure to a very pronounced hypoechoic cavity, especially in the preovulatory period.

In some cases, at a certain distance from the endocervix, closer to the external yaw are located cystic thin-walled rounded cavities reaching 20-30 mm in diameter (Ovulae Nabothi). In close proximity along the cervical can identify the fluid structures of various sizes, according to most researchers, are endocervical glands, enlarged due to obstruction.

Normally, the size and shape of the uterus vary widely, depending on the parity and condition of the reproductive system. To the childbearing period the uterus on the echogram represents the formation of a pear-shaped form, its length reaches 6 cm, the anteroposterior size is 4 cm.

In women giving birth, all the sizes of the uterus are increased by 0.7-1.2 cm. In postmenopause, the size of the uterus decreases.

Assessment of the state of myometrium. In the myometrium, 3 zones are distinguished.

The internal (hypoechoic) zone is the most vascularized part of the myometrium surrounding the echogenic endometrium. The middle (echogenic) zone is separated from the outer layer of myometrium by the blood vessels.

An important indicator is the so-called middle uterine echo (M-echo), which represents the reflection of ultrasonic waves from the endometrium and the walls of the uterine cavity. Its shape, contours, internal structure and anteroposterior size are evaluated - a parameter representing the greatest diagnostic value in pathological conditions of the endometrium. In interpreting this criterion it is necessary to take into account the patient's age, the phase of the menstrual cycle in women of reproductive age, in the presence of uterine bleeding - its duration, individual characteristics.

Isolate 4 degrees, corresponding to the ultrasound picture, characterizing the physiological processes in the endometrium:

• Degree 0. The median structure of the uterus appears as a linear echo with a high acoustic density; is determined in the early proliferative phase of the menstrual cycle and indicates a low content of estrogens in the body.
• Degree 1. The linear M-echo is surrounded by an echopositive rim, caused by edema of the stroma of the mucous membrane of the uterine cavity; is determined in the late follicular phase: under the influence of estrogens, there is a sharp increase in the size of the tubular glands with a thickening of the endometrium.
• Degree 2 is characterized by an increase in the echogenicity of the distal M-echo zone (directly adjacent to the endometrium). Usually this type of echogram happens in the preovulatory period and reflects the completion of maturation of the dominant follicle, coinciding with an increase in the content of progesterone.
• Degree 3. The middle M-echo is defined as a homogeneous pronounced hyperechoic structure and corresponds to the secretory phase of the ovarian-menstrual cycle; The ultrasound picture is explained by the increased concentration of glycogen in the endometrial glands caused by the action of progesterone

A simpler interpretation of the echogram according to the phases of the menstrual cycle is suggested by Timor-Trisch and Rottem (1991). During menstruation, the endometrium is represented by a thin interrupted echogenic line, dense hypoechoic structures (blood clots) are visualized in the uterine cavity. In the proliferative phase of the menstrual cycle, the thickness of the endometrium, which is isoechoic with respect to the myometrium, is 4-8 mm. In the perivascular period of the endometrium, a three-line echo can be represented. In the secretory phase of the menstrual cycle, the thickness of the echogenic endometrium ranges from 8 to 14 mm.

After menopause, the endometrium is usually thin (less than 10 mm in anteroposterior section). Atrophic endometrium is characterized on an echogram with a thickness of less than 5 mm. In post-menopause, the M-echo can be visualized in a transabdominal study in 27-30% of cases, while in the transvaginal study it is 97-100%. Sometimes a small amount of liquid (2-3 ml) can be detected in the uterine cavity.

The main vessels of the small pelvis, accessible visualization using transvaginal ultrasound and used in the diagnosis of uterine pathology, - uterine arteries and veins, as well as vessels of the endometrium. Uterine vessels are usually easily visualized at the level of the internal pharynx, closer to the lateral walls of the uterus. Dopplerometric blood flow studies in these vessels allow us to evaluate the perfusion of the uterus.

Numerous studies have shown changes in the blood flow velocity curves in the uterine artery as a function of the menstrual cycle: a marked decrease in the pulsation index and the resistance index in the luteal phase. There is no consensus on the changes in the blood flow in the uterine artery in the period of the period. However, in order to correctly interpret the data of the blood flow study, the circadian rhythm of the pulsation index in the uterine artery in the period of the period is worth noting: the pulsation index is reliably lower in the morning than in the evening (it rises during the day).

Available for visualization with transvaginal ultrasound and color Doppler imaging intra- and subendometric vessels of the endometrium. Establishing the presence or absence of blood flow is the simplest study, which nevertheless gives the most valuable information about the state of the endometrium. Thus, the absence of blood flow in subendometric vessels Zaidi et al. (1995) explain the failure in embryo transfer during in vitro fertilization.

The depth of the vascular penetration of the endometrium is assessed for the greater part of the endometrium with pulsating vessels. In the presence of a three-layered endometrium (a period of the period of the cerebral period), to evaluate the degree of vascular penetration of the uterus, the classification of Applebaum (1993) according to the zones is used:

• Zone 1 - the vessels permeate the outer hypoechoic layer of the myometrium surrounding the endometrium, but do not penetrate the hyperechoic outer layer of the endometrium.
• Zone 2 - the vessels penetrate the hyperechoic outer layer of the endometrium.
• Zone 3 - the vessels penetrate the hypoechogenic interior of the endometrium.
• Zone 4 - the vessels reach the cavity of the endometrium.