Diagnostic Gynecologic Procedures

34.1 Saline Infusion Sonohysterography

Description and Clinical Features

A saline infusion sonohysterogram (SIS), or more simply called a sonohysterogram (SHG), is a procedure in which the uterus is scanned during and immediately after instillation of saline into the uterine cavity. By outlining the inner surface of the endometrium, this procedure enhances the ability of ultrasound to detect and characterize endometrial pathology. As such, SIS can be helpful in a number of settings, including the following:

A postmenopausal woman with vaginal bleeding and a thickened endometrium on transvaginal sonography, in whom biopsy is planned: SIS can determine whether the thickening is focal or diffuse, thus aiding in the selection of an appropriate biopsy technique.
A woman with a normal-appearing endometrium on transvaginal sonography but with a high clinical suspicion of endometrial pathology: SIS is more sensitive for endometrial pathology and hence may detect pathology that was not found on standard sonography.
A woman clinically suspected of having endometrial adhesions: adhesions are visible on SIS but not on standard sonography.
A woman with fibroids that are suspected to be submucosal but whose location is uncertain on standard sonography: The location of fibroids in relation to the uterine cavity is more accurately assessed with saline in the endometrial cavity.

In women of reproductive age, it is important to schedule the SIS 5–9 days after the start of menses, to be sure the patient is not pregnant, in order to avoid potential damage to a very early pregnancy.

Sonography

The SIS procedure begins with the insertion of a catheter through the cervix into the uterine cavity. Some practitioners use a catheter with a balloon near its end, and inflate the balloon with saline to prevent the catheter from being dislodged and to decrease saline flow out through the cervix. Others find an insemination catheter without a balloon is sufficient to perform the study. Once the catheter is in place, a transvaginal transducer is inserted, followed by instillation of approximately 3–10 ml of saline through the catheter. The endometrium is scanned in sagittal and coronal (transverse) planes during and after saline instillation. Care must be taken to visualize the entire endometrium, sweeping from one side to the other sagittally and from anterior to posterior coronally. Alternatively, 3D sonography
can be used to assess the endometrium while saline is present in the uterine cavity. Once a 3D volume of the entire endometrial cavity is obtained, the endometrium can be assessed in detail after the transvaginal probe has been removed through rendering of the stored volume. Because the injected saline generally drains out of the uterine cavity fairly quickly (via the fallopian tubes and/or cervix), more than one instillation of saline may be needed during the procedure to ensure adequate visualization of the entire endometrial cavity. If the catheter has an inflated balloon, the balloon should be deflated toward the end of the procedure so that the lower segment endometrium can be assessed.

Figure 34.1.1 Normal saline infusion sonohysterogram. A: Sagittal transvaginal view of the uterus demonstrates fluid (*) that was instilled via a transcervical catheter into the uterine cavity. The inner surface of the endometrium (arrowheads), outlined by the fluid, is smooth with uniform thickness. B: The single-layer endometrial thickness (calipers) is slightly over 1 mm on each side.

On a normal SIS, the endometrium is homogeneous in appearance with uniform thickness and a smooth inner surface (Figure 34.1.1). In a woman of menstrual age, the endometrial thickness varies with the menstrual cycle; it is thinnest in the early proliferative phase and thickest in the secretory phase. In a postmenopausal woman, each side of the endometrium is normally less than 2 mm in thickness (note that this refers to single-thickness measurement as opposed to the double-thickness measurement used to measure the endometrium on a standard sonogram without saline).

Figure 34.1.2 Saline infusion sonohysterogram demonstrating diffuse endometrial thickening. A: Sagittal transvaginal view of the uterus in a woman with postmenopausal bleeding reveals a thickened endometrium (calipers) measuring 12.8 mm. B: After instillation of saline (*), the endometrium is seen to be diffusely thick (calipers).

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