Where Next for the Endoscope?

Ricardo A. Natalin; Jaime Landman

Disclosures
In This Article

Virtual Endoscopy

Virtual endoscopy utilizes three-dimensional computer-enhanced reconstruction of CT and MRI anatomical information to generate images that recreate the endoscopic perspective with great detail (Figure 6). This type of computer-driven reconstruction has been applied to the majority of luminal structures in the human body, including the urinary tract.[24] It potentially represents an inexpensive and noninvasive technique to evaluate the urinary tract.

Figure 6.

Virtual ureteroscopy image of urothelial tumor, created from a CT scan.

Owing to the high recurrence rate of bladder cancer, close cystoscopic surveillance after transurethral resection is currently the standard of care to establish early diagnosis of recurrence and to improve cancer control.[25] Standard cystoscopy, however, even with contemporary diminutive flexible instrumentation, results in some discomfort for the patient and can cause morbidity such as infection, bladder perforation, scarring, and stricture of the urethra.

At present, virtual endoscopy does not offer sufficient sensitivity to replace conventional cystoscopic evaluation in this setting. However, virtual cystoscopy is a feasible technique for the detection of bladder lesions smaller than 5 mm. Virtual imaging of the urinary bladder, in multiple planes and with a 360° view, currently allows difficult areas of the bladder to be accessed. At present, the major application of virtual cystoscopy is in patients for whom conventional cystoscopy is not applicable or is contraindicated.[26] Kivrak and colleagues found that, in selected patients, virtual cystoscopy can be successfully used for noninvasive detection of bladder lesions with a sensitivity of 90% and specificity of 94%.[26] Lopes and co-workers reported similar results, with a sensitivity of 95.1% and specificity of 91.2%.[27] These authors justifiably point out, however, that virtual cystoscopy will not be able to detect flat lesions such as carcinoma in situ, and does not afford the surgeon the opportunity to biopsy suspicious lesions.

Multidetector CT urography is an accurate, noninvasive imaging approach for diagnosing TCC in patients with gross hematuria; this technique has higher sensitivity than conventional excretory urography.[28] The initial clinical experience with virtual CT nephroscopy (a modality based on CT urography) was reported by Takebayashi and colleagues, who assessed 32 patients with suspected renal pelvic tumor. CT nephroscopy revealed 22 of 24 tumors (92%) while axial CT detected only 20 (83%) lesions. Virtual nephroscopy was also superior to axial CT in detecting pedunculated and infiltrating lesions.[29]

Impressed by the fine detail of the ureteric anatomy seen in this study, these same authors subsequently presented a similar study of 16 patients with suspected ureteral tumors. Virtual ureteroscopy successfully detected the presence of ureteral tumor, with a sensitivity and specificity of 81% and 100%, respectively. Additionally, virtual ureteroscopy facilitated the evaluation of extrinsic compression by lymphadenopathy and could be used to differentiate strictures from urothelial tumors.[30]

Contemporary data on virtual urologic endoscopy have shown that virtual ureteroscopy is safe, noninvasive and enables effective endoluminal navigation of the entire ureter. Battista et al.[31] concluded that virtual ureteroscopy provides superior anatomic information to that obtained by axial CT.

Despite the many potential advantages of virtual endoscopy using CT urography, limitations remain. Perhaps the most critical are the inability to identify alterations in mucosal texture and color and to administer treatment. Important pathology such as carcinoma in situ is unlikely to be identified with contemporary virtual endoscopy. While urinary cytology can be used to identify the majority of carcinoma in situ, the poor sensitivity of CT urography for identifying bladder pathology continues to support the use of cystoscopy in the majority of patients.

Magnetic resonance urography is a noninvasive diagnostic imaging technique which, unlike CT urography, does not require the application of ionizing radiation or iodinated contrast. T2-weighted magnetic resonance urography is the first relevant means of visualizing the urinary tract with MRI; the static fluid within the urinary tract is visualized as though it was a structure of the body for the purposes of image reconstruction. Magnetic resonance urography using gadolinium-based contrast material and T1-weighted images yields a bright appearance of urine. In conditions of low urine output, imaging is suboptimal. As such, intravenous diuretic administration is recommended when possible to enhance the quality of excretory magnetic resonance urography images under these conditions.[32]

As with CT urography, magnetic resonance urography has significant limitations, including a relative insensitivity for detection of renal calculi, a lengthy image-acquisition period, significant movement artifacts and lower spatial resolution when compared with CT.

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