1 Department of Perinatology, Kagawa Medical University, 17501 Ikenobe, Miki, Kagawa 761-0793, and 2 Department of Obstetrics and Gynecology, Shimane Medical University, Izumo 693, Japan
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Abstract |
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Key words: 2D ultrasonography/3D ultrasonography/ovarian cancer/tumours
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Introduction |
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Three-dimensional (3D) ultrasonography has been introduced into clinical practice in gynaecology. This technique overcomes anatomical limitations which restrict the number and orientation of the scanning planes on transvaginal sonography (Jurkovik et al., 1994). This ultrasonic innovation has diverse applications, e.g. detection of congenital uterine abnormalities (Jurkovik et al., 1995), evaluation of ovarian masses (Bonilla-Musoles et al., 1995
), assessment of uterine cavity pathology (Weinraub et al., 1996
), and ovarian and endometrial volume measurements (Kyei-Mensah et al., 1996
). Recently, further technical development of 3D technology has led to a self-contained imaging system that can not only produce conventional two-dimensional (2D) images but can generate within seconds a high-quality 3D image with no need for an external workstation or other additional, costly equipment (Baba et al., 1996
; Hata et al., 1997
). The objectives of our study were to demonstrate the feasibility of intratumoral surface visualization of ovarian tumours using 3D surface rendering and to determine whether 3D ultrasonography is valid in differentiating malignant from benign ovarian tumours and whether this method has a higher diagnostic accuracy than 2D ultrasonography.
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Materials and methods |
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All patients were studied with a specially developed abdominal 3D ultrasonography transducer (Aloka ASU-1000B, 3.5 MHz; Aloka, Tokyo, Japan). This ultrasonic transducer is connected to an ultrasonography device (Aloka SSD-1700; Aloka). This imaging system can provide conventional 2D ultrasonographic images and can also generate within seconds high-quality 3D images in the surface and transparent mode with no need for an external workstation. A 3D image is built by selecting a region of interest from a 2D image and superimposing on it a volume box defined by the examiner. The crystal array of the transducer then sweeps mechanically over the 2D region selected through a 60° angle. Within 5 s, the outlined volume is automatically scanned and a sculpture-like 3D image is displayed simultaneously on the screen. In this system (Vol-mode), the ultrasound beam is regarded as a projection ray in volume rendering, and ray tracing is conducted in real time. The procedure was not as complex as that of conventional 3D ultrasonography, and images can be obtained immediately (Baba et al., 1996; Hata et al., 1997
). At present we use a 128 MB removable hard disk drive for the permanent storage of 3D images.
First one examiner (A.M.) recorded the 2D ultrasonographic images with transabdominal and transvaginal approach, then another examiner (T.H.) recorded the 3D ultrasonographic images without knowing the results of the 2D study. A 2D ultrasonographic diagnosis of malignancy was done using the scoring system by Sassone et al. (1991). The scores of nine or more were regarded as malignancy. The surface rendering mode of the 3D ultrasonography allows the study of the inner wall surfaces of the tumour. Diagnostic criteria for ovarian malignancy by 3D ultrasonography were irregular thick septa (Figure 1), irregular papillary projection (Figure 2
), high echogenicity (Figure 2
), irregular inner wall (Figure 2
), and mostly solid irregular tumour (Figure 3
). Each variable was assigned as one point in 3D scoring. Ovarian tumours with two and more 3D diagnostic criteria (2 or greater in scoring) were defined as malignancy. Unfortunately, in this study, other indices such as Doppler evaluation of these tumours or serum screening, e.g. CA 125 were not carried out in these patients.
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Results |
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Discussion |
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In this investigation, we compared 3D ultrasonographic findings with 2D ultrasonographic findings for detecting ovarian malignancy. There were no significant differences for sensitivity, negative predictive value, and false negative rate between 3D and 2D ultrasonography. The positive predictive value (46.6%) of 2D ultrasound is lower than that (87.5%) of 3D ultrasound, but there was no significant difference. Compared with 2D ultrasound, 3D ultrasound had significantly higher specificity and accuracy, and significantly lower false positive rate. Bonilla-Musoles et al. (1995) reported that 2D ultrasound detected four out of five ovarian malignancies, and one additional ovarian carcinoma was diagnosed by 3D scanning. In this study, 2D ultrasonographic diagnosis of malignancy was carried out using the scoring system by Sassone et al. (1991). Lerner et al. (1994) pointed out that Sassone's scoring system is plagued by the existence of complex and high scoring lesions that are associated with benign lesions, such as teratoma and fibroma. In particular, the specificity and positive predictive value were hampered by masses that obviously were benign but nonetheless scored high, such as benign cystic teratoma and fibromathecoma. In this study, five of the 20 patients studied had benign cystic teratoma. The low specificity and low positive predictive value using 2D ultrasound in this study may be due to this population study bias. On the other hand, there was only one false positive diagnosis with 3D ultrasound in a patient with seromucinous cystadenoma. In order to evaluate the 3D imaging system in the diagnosis and differentiation of benign/malignant ovarian tumours, the same scoring system should be used for both the 2D and the 3D images. However, in this study, we used only the surface rendering mode for detection of ovarian tumour structures, and did not use planar images. Hence, we could not use the same scoring system for both the 2D and the 3D images. There are various scoring systems for 2D images, and different diagnostic criteria are used for these scoring systems, Therefore, there are primary differences between the various 2D scoring systems, as there are between the 3D and 2D scoring systems used in this study. Moreover, the scoring system of Sassone et al. (1991) is the most useful standard scoring system for 2D imaging in the diagnosis and differentiation of benign/malignant ovarian tumours, and we did not try to compare other scoring systems for 2D images with our 3D scoring system. We believe that 3D ultrasonography provides novel information on the visualization of intratumoral structures of the ovarian masses. These results suggest that 3D ultrasonography has the potential to be a supplement to 2D ultrasonography and might be useful in identifying malignant ovarian tumours. However, in view of the small number of ovarian tumours, these observations must be considered preliminary.
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Notes |
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References |
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Submitted on July 9, 1998; accepted on November 30, 1998.