UTERINE ULTRASOUND IMAGING


Pelvic sonography can be performed using two approaches.

  • The transabdominal approach requires the patient to have a filled urinary bladder.

  • The transvaginal approach is performed on patients with an empty urinary bladder.

Regardless of the approach, a number of characteristics are noted during the examination. These include the following:

  • Size measured in three dimensions (consider age and parity)

  • Echogenicity of myometrium

  • Uterine shape

  • Orientation (anteverted, retroverted)

  • Location (midline, deviated to the right or left)

  • Borders (smooth or irregular)

  • Location and echogenicity of masses

  • Endometrial layer (size and echogenicity)

  • Presence of fluid, masses, air, or foreign bodies within endometrial cavity

METHODS

THE TRANSABDOMINAL APPROACH

Allows for a more global view of the pelvis. This is especially helpful when performing an examination for an enlarged uterus or pelvic mass. When performing transabdominal imaging, the transducer is usually of low to medium range of frequencies. The highest frequency transducer, which provides optimal penetration of tissue, is used.

THE TRANSVAGINAL APPROACH

When using the transvaginal approach, the transducer is at a higher frequency, which allows for better resolution of the endometrial cavity and ovaries but at a loss of penetration. Also, the field-of-view is more limited with the transvaginal probe.

Transabdominal and transvaginal imaging methods complement each other. Transabdominal imaging should be performed routinely and transvaginal imaging when necessary to supplement an examination to avoid diagnostic errors.

Some contraindications for using transvaginal scanning include patients who are virgins or unconscious, who have psychological problems, who are under the influence of controlled substances, or obstetrical patients who might have a placenta previa.

BASICS

NORMAL SONOGRAPHY OF THE UTERUS

  • Divided into fundus, corpus, isthmus, and cervix

  • Size and contour (shape) vary with age, hormonal status, and parity.

  • Mean measurements for nulliparous female is 8 × 5 × 4 cm (length × width × Anterior and Posterior (AP) diameter)

  • Parity may increase each dimension by more than 1 cm.

LAYERS OF THE UTERUS

  • Perimetrium: not visualized

  • Myometrium: homogeneous, midlevel echoes

  • Endometrium:

  • Midline endometrial stripe represents interface between two endometrial layers; appears as thin echogenic line.

  • Thickness and echogenicity vary with phase of menstrual cycle and age.

THE VAGINA

  • Midlevel echoes similar to the myometrium

  • Midline echogenic stripe represents interface between the walls of the vagina.

MEASUREMENT OF THE ENDOMETRIUM

  • Endometrium measured on midline sagittal plane of the uterus in A/P dimension

  • Both anterior and posterior layers of endometrium included in measurement

  • Outer hypoechoic layer represents the inner layer of myometrium and not included in measurement

  • May see acoustic enhancement posterior to endometrial layer

The Menstrual Cycle—Sonographic Appearances of Endometrium

Menstrual Phase

  • Variable appearance

  • Endometrial cavity may contain menstrual contents that may appear anechoic, complex, or echogenic.

  • May see thin, broken echogenic midline stripe

Proliferative Phase

  • Functional layers are hypoechoic.

  • 4–8 mm in AP diameter

Late Proliferative/Periovulatory Phase

  • Triple-layer appearance: central echogenic line, adjacent thicker hypoechoic functional layers, and outer echogenic basal layers

  • 6–10 mm in AP diameter

Secretory Phase

  • 7–14 mm in AP diameter

  • Thickened hyperechoic endometrium

Postmenopausal Endometrium—Asymptomatic Female

  • Thin echogenic line

  • Approximately less than 5 mm in A/P diameter

Uterine Location and Positions

  • Located in midline or deviated to right or left side

  • Anteverted (most common position) and/or anteflexed

  • Retroverted and/or retroflexed

  • Overdistended urinary bladder may deviate uterus to either side.

Common Congenital Variations Seen on Ultrasound

Septate/Subseptate Uterus (Most Common)

  • Partial or complete failure of resorption of median septum

  • Partial or complete duplication of uterine cavities without duplication of uterine horns

  • Can visualize two endometrial echoes

  • Endometrial echoes closely related and separated by thin fibrous septum

  • Outline of uterus appears normal.

Bicornuate Uterus

  • Duplicationofuterinehornsandsometimescervix

  • Bilobed uterine cavity seen

  • Can visualize two endometrial echoes and sometimes endocervical echoes

  • Endometrial echoes widely separated

  • Deep indentation (greater than 10 mm) on fundal contour of uterus

Uterine Didelphys

  • Complete duplication of uterus, cervix, and vagina

  • Can visualize two endometrial echoes

  • Endometrial echoes widely separated

  • Can visualize two endocervical echoes

  • May have hypoechoic fibrous bands of tissue connecting both uteri

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