General discussion of the principles of ultrasonagraphy are found in Chap.295. Transabdominal and transvaginal imaging are complementary studies in evaluating the female pelvis. Transabdominal sonography gives a good overview of the pelvis but requires a full urinary bladder. When the bladder is full, it acts as an acoustic window to the pelvis for transabdominal scanning. If empty, retrograde filling of the bladder with 300 to 500 mL of saline, with careful avoidance of introducing air, may be necessary to obtain adequate visualization. In contrast, transvaginal sonography is performed with an empty bladder, which is more comfortable for the patient. Transabdominal scanning of the pelvis is usually performed with lower-frequency transducers (3 to 3.5 MHz) that provide a larger field of view and deeper penetration but with lower resolution. Transvaginal images generally provide better resolution with a smaller field of view, since the transducer is placed closer to the area of interest and utilizes a higher-frequency probe (5 to 7.5 MHz). The standard transabdominal views are longitudinal and transverse and the orientation of the pelvic anatomy is relatively simple (Fig 109-1 and Fig 109-2). Standard transvaginal views are sagittal and coronal; however, orientation of pelvic anatomy is initially more difficult (Fig 109-3). Identifying the anatomy of the uterus before searching for other pelvic structures may assist in obtaining transvaginal images.
FIG. 109-1. Normal longitudinal pelvic anatomy. The uterus (left) and the vagina (right) are seen posterior to the anechoic bladder on a transabdominal longitudinal view. The cervix lies immediately posterior to the angle (deepest part) of the bladder.
FIG. 109-2. Normal transverse pelvic anatomy. The uterus is seen posterior to the bladder on a transabdominal scan in the transverse plane. The margins of the uterus are marked by plus signs and the arrow points to the endometrial stripe.
FIG. 109-3. Normal uterus. The midline endometrial stripe is seen at both ends of the uterus on a transvaginal sagittal view. The posterior uterine wall is clearly seen. The tip of the ultrasound probe is very close to the anterior wall of the uterus on this view.
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