GE Healthcare Ultrasound Virtual Cystoscopy Using Volume Ultrasound By Nirvikar Dahiya, MD imagination at work
Introduction The urinary bladder has been imaged by multiple modalities over the years. It has been accepted that conventional cystoscopy is the best way to visualize lesions in the lumen of the urinary bladder or along the mucosal wall. With the advent of 3D technologies in multiple modalities including MRI, CT and Ultrasound, the ability to render surfaces has opened a new field of noninvasive assessment of the bladder, in a manner very similar to conventional cystoscopy. Ultrasound is unique in this group because it can generate volume acquisitions with physiological distension of the urinary bladder. No additional procedures are needed, such as the insufflation of CO 2 for CT renderings. Ultrasound is also the most cost-effective of all imaging techniques, including conventional cystoscopy. This could translate into a large potential cost-savings for healthcare providers. The simplicity of acquisition using volume transducers may also enhance productivity once the initial learning curve is surpassed. Volume rendering uses an entire volume of data, summing the contribution of each pixel along a line from the viewer s eye through the data set, displaying the resulting composite voxel. Volume Ultrasound, which includes 3D and 4D, additionally lets users do this in real-time, in a manner similar to a urologist manipulating a cystoscope. We evaluated Virtual Cystoscopy using Volume Ultrasound in a group of patients and correlated results with conventional cystoscopic findings. The patients chosen had known bladder lesions on 2D ultrasound. Volume Ultrasound was performed to ascertain whether any additional information could be found. We also determined that Volume Ultrasound increased the diagnostic confidence of the radiologist. Our results lead us to believe that this exciting new field of Volume Ultrasound is a very valuable adjunct to 2D ultrasound imaging. Normal Urinary Bladder and 2D Sonographic Anatomy The urinary bladder is located in the lower pelvic cavity anterior to the peritoneal cavity and posterior to the pubic bone. Superiorly, the peritoneum is reflected over the anterior aspect of the bladder. The ureteric and urethral orifices demarcate an area known as the trigone. The urethral orifice marks the area known as the bladder neck. The bladder neck and the trigone maintain a constant shape and position. The bladder wall consists of the mucosa, three muscular layers, and the adventitial layer. Ultrasound shows the urinary bladder as an anechoic structure when filled with urine. However, the 2D assessment (Fig 1) leaves many unanswered questions, such as the status of the trigone; the true extent of a tumor on the wall, if present; and the relationship of a lesion to the urethral and ureteral orifices. Fig 1: 2D images showing transverse sections of the urinary bladder. The ureteral orifices appear as mild elevations on the bladder base and the urethral orifice appears as a mild depression. Conventional Cystoscopy Conventional cystoscopy is the most basic of all endourological procedures using either a rigid or flexible endoscope. A complete survey includes the trigone; ureteral orifices; the posterior, lateral and anterior walls; and the dome of the bladder. An example of a normal cystoscopy demonstrates the ureteral orifices and the associated ureteric ridge on either side that represents the intramural extension of the distal ureter as it enters through the bladder wall (Fig 2). Nirvikar Dahiya, MD Director, Department of Ultrasound KG Hospital and Post-graduate Institute Coimbatore, India Fig 2: The ureteral opening on conventional cystoscopy with the elevated ridge.
Virtual Cystoscopy using Volume Ultrasound Volume Ultrasound deals with the acquisition of large volumes of ultrasound data. This block of information can be viewed in many ways, such as sagittal, transverse and coronal, or as a complete, volumerendered image. To render a surface, it is necessary to have fluid in front of it. For example, the urinary bladder mucosal must be rendered while the bladder is full of urine. The resulting image lets us to look at the mucosal surface, and also allows for a complete view of the bladder base. This is significant because it allows us to virtually image the bladder trigone sonographically for the first time (Fig 3). images were taken using a volume angle of 60 to 70 degrees. The rendering settings used were a combination of surface smooth and surface texture. One radiologist with experience in Volume Ultrasound, blinded to the results of conventional cystoscopy reviewed the images. Cases 1 7 The following is a brief account of the cases we saw on Virtual Cystoscopy using Volume Ultrasound. Case 1: A 23-year old male with recurrent episodes of urinary tract infection (UTI) was sent for a routine ultrasound scan after other investigations revealed bilateral vesicoureteric (VU) reflux. The conventional cystoscope showed bilateral patulous ureteral orifices. Using Volume Ultrasound, the rendered view showed the patulous openings of the ureter into the urinary bladder. These wide spread openings, probably congenital, were the cause of VU reflux (Fig 4). The rendered views could not have been replicated by a 2D scan and were comparable to conventional cystoscopy (Fig 4a). Fig 3: 3D ultrasound surface rendering of the bladder base shows a bird s-eye view of the bladder base at the trigone (demarcated by arrowheads). The upper two arrowheads correspond to ureteral orifices, while the lower single arrowhead points towards the urethral orifice. In males, it is easier to visualize the urethral opening in the sagittal view, since the prostate can be used to orient the bladder base. In females, a very acute angulation behind the pubic bone is required to visualize the urethral orifice. This is problematic in 2D imaging due to the difficulty of positioning the probe, but this is overcome when using volume imaging. Volume Ultrasound not only helps us look at the trigone of the bladder, ureteric ridges and urethral openings but also allows us to study in detail the ureteric orifices, especially when they are patulous in nature. Lesions that arise from the bladder wall can be better characterized and more clearly show their spatial relationship. Additionally, the bladder can be sectioned in any plane to visualize structures behind or below the bladder. This gives better visualization of pathology extending to or involving adjacent structures. Fig 4: Arrowheads show the patulous ureteric openings in this case of VU reflux disease. The long arrow points to the urethral orifice. Materials and Methods Twenty four patients with known bladder lesions underwent Virtual Cystoscopy using Volume Ultrasound and a conventional cystoscopy protocol. A distended bladder was used to obtain a good acoustic window. A volume transducer (4D3C) at 4Mhz on a LOGIQ 9 ultrasound system (GE Healthcare, Milwaukee, Wisconsin) was used for the acquisitions. A surface rendering of the lumen was obtained. All Fig 4a: The right and left ureteric orifices, sono-cystoscopic (top) and conventional cystoscopic (bottom) views.
Case 2: A middle-aged male presented with a diagnosis of left-sided ureterocele. We performed a volume rendering of the trigone region to determine whether Virtual Cystoscopy using Volume Ultrasound could show the bulge of the ureterocele as clearly as cystoscopy. The rendered image on Volume Ultrasound compared favorably with the cystoscopy (Fig 5 and Fig 5a). Case 4: A 62-year old male with known prostate hypertrophy was diagnosed with prostatic abscesses by demonstrating multiple hypoechoic areas in 2D ultrasound. The enlarged prostate was elevating the bladder base and distorting the urethral orifice, making it look slightly patulous. A volume-rendered image of the bladder base was obtained (Fig 7), and proved to be more diagnostic than the conventional cystoscopic evaluation. The urethral orifice was not well demonstrated in the cytoscopic examination because of distortion of the trigone by the underlying enlarged prostate (Fig 7a). Fig 5: The small elevation of the intramural portion of the left ureter is rendered on a sono-cystoscopic view and the sectional planes demonstrates a ureterocele. Fig 7: Sectional planes of the prostatic abscesses showing elevation of the bladder base and distortion of the urethral orifice making it more prominent in the rendered image (arrow). Fig 5a: Conventional cystoscopic view of the ureterocele. Case 3: A 23-year old female presented with lower abdominal pain. A 2D ultrasound showed a large adnexal hemorrhagic cyst (Fig 6). Cystoscopy demonstrated the external mass effect (Fig 6a) of the cyst on the posterior wall of the urinary bladder. Volume Ultrasound is presented here as a case in point that the external mass effect on the contour of the urinary bladder is well reflected in the sono-cystoscopic views. Fig 7a: Conventional cystoscopic view of the prostatic enlargement causing the mass effect. Case 5: A patient presented with known transitional cell carcinoma (TCC) on the wall of the urinary bladder. The irregular papillary surface is well demarcated on the volume-rendered image (Fig 8). Fig 6: 2D ultrasound image (left) and a volume-rendered image (right). The external mass effect of the ovarian cyst on the posterior wall of the urinary bladder is well appreciated on the sono-cystoscopic views. Fig 8: Small TCC (left) is seen as an irregular growth from the wall into the lumen. The urethral orifice (arrow) is shown to be well away from the lesion. Cystoscopic view (right) of the TCC. Fig 6a: Conventional cystoscopic view of the external mass effect.
Conclusions Case 6: An elderly man presented with an enlarged prostate and symptoms of urinary frequency. The 2D ultrasound demonstrated bladder wall hypertrophy with two small diverticula in the lateral walls. A volumerendered image was obtained to view the openings of the diverticula. Figure 9 shows the end-on view of the diverticulum s opening on the right side. This helped to better estimate the size of the neck of the diverticulum. Clinically it is important to know if the size is large enough to leave residual urine in the diverticulum after voiding. A 2D size estimation is not very accurate as it does not take circumferential measurements of the neck into consideration as the rendered image does. Virtual Cystoscopy using Volume Ultrasound is an emerging application used to detect bladder lesions. This technique is useful for diagnosing urinary bladder pathology as demonstrated in the cases presented. Benefits include a more comprehensive understanding of pathology when correlating 2D and volume information, thus providing increased diagnostic confidence. An additional benefit is the reduction of patient discomfort and the cost savings of potentially eliminating the need for an invasive examination. This is especially true when considering follow up cystoscopies after a therapeutic cystoscopy or surgery. In a different series of patients, we were able to cancel 9 out of 10 cases scheduled for a followup conventional cystoscopy after Virtual Cystocopy. Volume Ultrasound provided the information necessary to make the diagnosis. In our practice Volume Ultrasound has proven to be a valuable diagnostic tool adjunct to 2D ultrasound. In addition, it has the potential to reduce the number of invasive procedures in the future, with significant impact on the efficacy and efficiency of urological patient care. Acknowledgements Fig 9: Urinary bladder diverticulum. The 2D image (inset) and the volume-rendered image of the bladder wall show the end-on view of the diverticulum opening on the right lateral wall of the bladder (arrowheads). Case 7: A 42-year old male presented with a mobile urinary bladder calculus. The calculus was approximately 1.5 cm in size and showed mobility with a change in patient position (Fig 10). Another case of a smaller vesicular calculus is also shown (Fig 10a). Fig 10: Large intra vesicular calculus 2D and 3D images. Fig 10a: Another smaller calculus. Sono-cystoscopic (left) and conventional cystoscopic view (right). I am extremely grateful to Dr. M Ramalingam MS, MCh and Dr. MG Pai MS, Consultant Urologists at the KG Hospital and Post-Graduate Institute, and Dr. K Senthil MCh, FRCS for their valuable insights and clinical inputs toward understanding conventional cystoscopy and for the correlation with the sono-cystoscopy views. References 1. Rankin RN, Fenster A, Downey DB, et al. Three-dimensional sonographic reconstruction: techniques and diagnostic applications. AJR Am J Roentgenol 1993;161:695. 2. Hamper UM, Trapanotto V, Sheth S et al. Three-dimensional ultrasound: preliminary clinical experience. Radiology 1994;191:397. 3. Riccabona M, Nelson TR,Pretorius DH, Davidson TE. In Vivo Threedimensional sonographic measurement of organ volume: validation in urinary bladder.j Ultrasound Med 1996;15:627-623 4. Flannigan GM. Editorial: imaging,stone disease. Curr Opin Urology 1997;7: U10-U12. 5. Sakr WA, Grignon DJ, Crissman JD. Histopathology of transitional cell carcinoma of the urinary bladder. Curr Opin Urology 1997; 7 : 287-292 6. Rasmussen SN, Haase L, Kjeldsen H, et al. Determination of renal volume by ultrasound scanning. J Clin Ultrasound 1978;6:160. 7. Jones TB, Ruddick LR, Harpen MD, et al. Ultrasonographic determination of renal mass and renal volume. J Ultrasound Med 1983;2:151. 8. Grossman H, Rosenberg ER, Bowie JD, et al. Sonographic diagnosis of renal cystic disease. AJR 1983;140:81 9. Brenner RJ, De Martini WJ, Goodling GAW, et al. Ultrasonic demonstration of a simple ureterocele and distal ureter in an adult. J Clin Ultrasound 1978;6:431. 10. Itzcha KY, Singer D, Fischelovitch Y. Ultrasonographic detection of bladder tumors. I. Tumor detection. J Urol 1981;126:31 11. Kawashima A, Goldmand SM. Neoplasms of the renal collecting system, pelvis, and ureters. In: Pollack HM, McClennan BL, editors. Clinical urography. Philadelphia,PA: W.B. Saunders, 2000:1561 641. 12. Merkle EM, Wunderlich A, Aschoff AJ, et al. Virtual cystoscopy based on helical CT scan datasets: perspectives and limitations. Br J Radiol 1998;71:262 7. 13. Song JH, Francis IR, Platt JF, et al. Bladder tumor detection at virtual cystoscopy. Radiology 2001;218:95 100. 14. Dahiya N. The Kidneys,Ureters and Bladder. In: Khurana A, Dahiya N, 3D&4D Ultrasound: A Text and Atlas. Anshan,U.K. 2004,pp 63-92.
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