Three‐dimensional ultrasound of deep infiltrating endometriosis involving the rectosigmoid colon

Sir, Recently, the use of three-dimensional (3D) ultrasound and characteristics of deep-infiltrating endometriosis in general have been described (1). We would like to call attention to the use of 3D-transvaginal ultrasound as a new diagnostic tool in patients with endometriosis involving the rectosigmoid colon. We have used a Voluson® E8 machine (GE Healthcare, Wauwatosa, WI, USA) with a 6–12 MHz vaginal probe. We located the rectosigmoid endometriosis by two-dimensional (2D) ultrasound by positioning the probe behind the cervix. Thickening of the regular smooth muscle layer (>3 mm) (2) of the rectosigmoid wall were located by up-down and side-to-side movements. Pressure on the vaginal probe was applied upon locating bowel endometriosis to reduce the distance from the probe to the lesion and thereby improve the image. Fine adjustments were made with regard to frequency, depth, brightness and contrast so the best-possible image quality was obtained. A 3D acquisition was performed when the position of the probe yielded a 2D picture containing the largest longitudinal measurement of the lesion. Data generated during a 3D scan are generally shown as a multiplanar display, providing the traditional 2D picture together with two picture sets perpendicular to this plane (Figure 1). The pictures can be scrolled through and thereby resemble a live scan in three dimensions. Moreover, 3D datasets enable evaluation of the same scan at a later time with slide-by-slide assessment of the images, such as in an MRI scan. Turning the pictures around the X, Y and Z axis improves spatial orientation and is presumably more illustrative to the viewer than looking at standard still pictures. A multiplanar image of infiltrating rectal endometriosis illustrating the thickening of the muscularis propria layer (star) in close relation to the cervix (circle) and an ovary (asterisk). The submucosa and mucosa appear as a hyperechoic rim (arrow). The regular rectal wall lies in continuation of the infiltrate (triangle). The opposite rectal wall is visible (square). Bottom right is a rough outline of the region of interest. Different 3D programs within the software of 4D View® (GE Healthcare, USA) provides multiple imaging options. Using Virtual Organ Computer-aided Analysis (VOCAL) data sets can be rotated around a fixed axis and through a number of rotation steps, and the observer can measure the volume of a certain structure (3) (Figure 2). In clinical practice, bowel endometriosis infiltrating more than 50% of the bowel wall usually requires segmental resection (4). This is an operation with a significant risk of complications, and VOCAL may contribute to the appropriate clinical decision by generating a good impression of the extent and volume of bowel wall infiltration. A 3D model of endometriosis in the rectum (of a hysterectomized woman) generated by using the VOCAL-imaging program rotating the A plane about the B plane. (a) The volume above right, rotated 90 degrees, (b) the above volume rotated 180 degrees. With the Render program (within the software of 4D View®), 3D data sets can be viewed as a whole (5). The interpreter must decide how large a portion of the dataset is needed to create a picture of optimal quality. The image gives the impression of depth because more slides are represented in this image than in a 2D image. Figure 3 shows a rendered view of rectal endometriosis. The most consistent 2D-ultrasound feature of endometriosis infiltrating the bowel is the presence of a hypoechoic irregular-shaped thickening of the muscularis propria layer, while the submucosa and mucosa appears hyperechoic (6). In a rendered image, the mucosa and submucosa becomes distinct, compared to the 2D image. This is achieved by a sharpening of the image contrasts. Therefore, with Render it might be easier to interpret which layers of the rectosigmoid wall are affected by endometriosis. A comparison of a regular ultrasound image (left) and a rendered view (right) of endometriosis in the rectal wall. Note the sharper contrasts that makes the rectal wall, submucosal and mucosal layer more apparent. Operative treatment of bowel endometriosis often involves colorectal surgeons. Preoperative diagnosis of rectal involvement is therefore pivotal for clinical planning and for counseling of the patient. Traditional 2D ultrasound is highly operator dependent and the examination results in still pictures, which can be difficult to interpret after the examination. The 3D ultrasound might facilitate surgical planning of the procedure. The possibility for analysis of the image sequence after the examination may also be of benefit to the patient. Thus, scanning time can be shortened as compared to standard-vaginal ultrasound (7), and thereby reducing the often-significant pain experienced during extended examinations. In conclusion, 3D-transvaginal ultrasound assessment of rectosigmoid endometriosis may contribute to improved diagnostic accuracy. It can potentially provide a better overview of the extent of in-growth into the bowel wall and contribute to the decision of which operation method to apply. Further investigations are needed to evaluate the possibilities of 3D-transvaginal ultrasound in a busy clinical setting. The Danish Endometriosis Society has kindly granted money for the software used for analyzing the 3D datasets.