In Vitro Uterine Strain Imaging: Preliminary Results

Uterine abnormalities tend to be clinically evident as dysfunctional uterine bleeding. Although most cases result from a benign etiology, approximately 10% to 30% of women with dysfunctional uterine bleeding will be found to have endometrial cancer.1 Three of the benign causes of dysfunctional uterine bleeding are leiomyomas (uterine fibroids), endometrial polyps, and adenomyosis. Leiomyomas are stiff growths of homogeneous tissue bundles of smooth muscle and can be differentiated from the normal myometrium by the presence of a capsule.2–4 Submucosal leiomyomas that project into the uterine cavity are thought to cause dysfunctional uterine bleeding because they usually expand the endometrial surface and disturb the regular shedding process.5 Adenomyosis is a condition in which the soft endometrial glands, smooth muscle cells, and stroma invade the myometrium, creating cysts in the tissue, and usually affects the posterior wall of the uterus.4,6 Endometrial polyps are focal hyperplastic growths of the endometrial glands and stroma, which may contain malignant cells.7 Ultrasound B-mode characteristics of leiomyomas, endometrial polyps, and adenomyosis can be compared to the surrounding normal uterine tissue. Compared to the myometrium, the basal layer of the endometrium is hyperechoic due to the specular reflections from the ramifying glands, whereas the functional layer of the endometrium is hypoechoic compared to the basal layer.8 Submucosal leiomyomas are usually hypoechoic compared to the myometrium,4,5,9 but as they become more heterogeneous due to the presence of degeneration, calcification, or necrosis, the heterogeneity of the echo structure also increases.10 When heterogeneous leiomyomas are present, it can be difficult to distinguish them from endometrial polyps, adenomyosis, blood, or mucus. Typical endometrial polyps are hyperechoic compared to the myometrium and isoechoic to the endometrium with a homogeneous echo texture.7,11 In transvaginal ultrasound images, adenomyosis appears as a hypoechoic region in the myometrium.10,12 For premenopausal women, dysfunctional uterine bleeding most often results from leiomyomas, endometrial polyps, and adenomyosis. These may have similar appearances on B-mode ultrasound scans, which can make differentiating between the conditions problematic with conventional ultrasound techniques, especially when there are diffuse echo texture changes.10,12 This differentiation, however, is clinically important because treatment for the 3 conditions differs considerably. Currently, magnetic resonance imaging (MRI) is widely accepted as the most capable modality for distinguishing between adenomyosis and leiomyomas.13,14 However, MRI studies are expensive and may be unavailable to some patients, preventing MRI from being a first choice for screening the large number of patients with dysfunctional bleeding. For postmenopausal women, the main causes of dysfunctional uterine bleeding are endometrial polyps, endometrial cancer, endometrial hyperplasia (or atrophy), and leiomyomas.4 Endometrial cancer shares a symptom of abnormal uterine bleeding with benign conditions.1,13,15 Endometrial biopsies are generally used to diagnose endometrial cancer because they sample a significant portion of the endometrial lining.16 However, current diagnostic techniques, including endometrial biopsy, do not allow differentiation between other sources of dysfunctional uterine bleeding, especially when more than 1 of these conditions is present. Due to the differences in their tissue orientation and makeup, the treatment options vary for leiomyomas, endometrial polyps, and adenomyosis.3,5,11,12,17–19 Thus, finding a way to accurately diagnose the causes for abnormal uterine bleeding in vivo would allow the physician to decide on appropriate treatment methods to avoid unnecessary hysterectomies. Manual palpation is a form of diagnosis that has been used for centuries to differentiate between normal and abnormal conditions. However, palpation does not provide quantitative information that can be compared from one patient visit to the physician to the next and often cannot be easily performed on organs such as the uterus. Two imaging modalities, ultrasound strain imaging20–23 and magnetic resonance elastography,24–29 are being investigated for providing a more quantitative approach to palpation of organs accessible and inaccessible to manual palpation. Both modalities image the strain or stiffness distribution throughout an organ in response to an applied stress. Due to the differences in tissue makeup and stiffness between adenomyosis, endometrial polyps, and leiomyomas, ultrasound strain imaging may have the potential to provide additional diagnostic information by differentiating between these 3 conditions. In this article, we present preliminary results that illustrate the ability of in vitro ultrasound strain imaging to differentiate between leiomyomas and endometrial polyps on excised intact human uteri.