However, for an accurate evaluation of the much more prevalent but less severe distortions of uterine morphology within the context of congenital malformations, a coronal image of the uterus perpendicular to its long axis is required. The reference image comprises the outer and inner contour of the fundal myometrium and the beginning of the interstitial portion of the Fallopian tubes (Fig. 7.2). Ultrasound imaging is based upon reflection of high frequency sound waves at interfaces between tissues with different characteristics and a distinct endometrial line is necessary to delineate the uterine cavity from the myometrium. The quality of the ultrasound image will be optimal if the endometrium is thick, thus in the secretory or late proliferative phase of the menstrual cycle [2] (Fig. 7.3). If the endometrial echo is not distinct enough, sonohysterography, also called fluid instillation sonography or FIS, will enhance contrast so that the uterine cavity becomes clearly delineated. Saline or gel are negative ultrasound contrast agents, while gel foam containing micro-air bubbles acts as a positive ultrasound contrast agent [11] (Fig. 7.4). Sonohysterography implicates a speculum examination and insertion of a catheter through or in the cervical canal and causes more discomfort compared to a vaginal ultrasound examination only [12]. Sonohysterography isn’t an option if a vaginal approach is not possible or if the woman doesn’t consent to.

Ultrasound imaging implies cross sections through the uterine cavity and cervical canal as well as through the endometrium, myometrium and cervical wall whereas the outline of the uterus should be visible too. Any change of morphology is to be detected and the underlying cause should be elucidated too: e.g. a fibroid may distort the cavity and/or the uterine contour, an intracavitary structure may be a fibroid or a polyp, and a bulging wall may be due to adenomyosis (Fig. 7.5). A congenital anomaly can be evidenced too. To evaluate the more minor congenital uterine anomalies with 2D ultrasound, success in obtaining the reference image by an abdominal or by a vaginal approach, depends on the position of the uterus (Fig. 7.6). Transverse 2D images of the uterus can usually be obtained and an interrupted endometrial or cervical echo may be indicative of a fusion or a resorption anomaly. But these transverse images do not allow for a detailed evaluation of the degree of altered morphology (Fig. 7.7). With 3D ultrasound technology, the volume can be manipulated and any section through the volume can be made. The reference image can be obtained, irrespective of the position of the uterus in the acquired volume (Fig. 7.8). This explains why 3D imaging is essential for an accurate evaluation of the majority of congenital uterine and cervical anomalies by ultrasound. An important added value of 3D ultrasound is that a volume can be stored and exported allowing for reassessment, discussion and use in training programs. Contrary to 2D ultrasound, laparoscopy or hysteroscopy where one is restricted to the still images or videos taken at the moment of the examination, volume manipulation during off-line analysis allows for an infinite number of additional sections and information.