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
