IMAGING

Detection of Bladder Tumors with Dynamic Contrast-Enhanced MDCT
Jinzaki M, Tanimoto A, Shinmoto H, Horiguchi Y, Sato K, Kuribayashi S, Silverman SG
Department of Diagnostic Radiology, Keio University School of Medicine, Tokyo, Japan
AJR Am J Roentgenol. 2007; 188: 913-8

• Objective: In a small pilot study, we assessed whether early-phase dynamic contrast-enhanced MDCT can be used to detect bladder tumors and whether thin reconstruction improves the detection rate.
• Subjects and Methods: Thirty-six patients (30 with 59 cystoscopy-proven bladder cancers and six with normal bladders) underwent dynamic contrast-enhanced MDCT of the pelvis and abdomen. Images were obtained from the symphysis pubis to the diaphragm 70 seconds after injection of 100 mL of contrast medium. McNemar test was used to compare sensitivity per patient, segment, and tumor and specificity per patient and segment for each of three reconstruction methods: 5-mm sections with no overlap (i.e., 5-mm axial images), 2.5-mm sections with 1.25-mm overlap (i.e., thin-section axial images), and 2.5-mm sections with 1.25-mm overlap and multiplanar reformation (MPR) (i.e., thin-section axial images with MPR).
• Results: MDCT with a combination of thin, overlapped sections and MPR depicted all but one of 47 bladder tumors larger than 5 mm but only five of 12 tumors 5 mm or smaller. There were no false-positive findings. Per-tumor sensitivity was significantly better with thin-section images with MPR (90%) and thin-section images alone (86%) than with 5-mm axial images (80%) (p < 0.05). Per-segment sensitivity was significantly better with thin-section images with MPR (95%) and thin-section axial images alone (87%) than with 5-mm axial images (79%) (p < 0.05). Per-patient sensitivity and per-patient and per-segment specificity did not differ with the three methods.
• Conclusion: Dynamic contrast-enhanced MDCT of the pelvis shows promise for the detection of bladder tumors. Use of thin-section images with MPR and thin-section axial images alone had a significantly better rate of detection of bladder tumors than use of 5-mm axial images.
  
  
• Editorial Comment
  The authors show the ability of thin (2.5 mm) and overlapped sections and multiplanar reconstruction (MPR) to depict small bladder tumors. Thin-section images (2.5 mm) with MPR were used to detect all but one of 47 bladder tumors larger than 5 mm but only five of 12 tumors 5 mm or smaller. There were no false-positive findings. The sensitivity for detecting bladder tumors 5 mm or smaller was significantly better for thin-section images with MPR and thin-section axial images (both, 58%) than for 5-mm axial images (25%) (p < 0.05). Use of thin-section axial images improved the detection rate only for tumors smaller than 5 mm. MPR improved the detection of tumor in the bladder dome and tumors adjacent to normal anatomic structures.
  Multidetector CT-urography has been shown to be an effective single comprehensive examination in the evaluation of patients with hematuria or with risk for the development of urothelial malignancies. Since protocols for MDCT urography varies from each institution, most MDCT urography images are obtained in the unenhanced phase (detection of calculi), nephrographic-phase (detection of renal masses) and excretory-phase (detection of urothelial lesions). Some authors recommend that MDCT urography should be performed only after adequate cystoscopy since these protocols do not allow adequate evaluation of the bladder.
  Since January 2006, we have been using in our institution similar technique described by the authors as part of MDCT urography (1). This additional phase of MDCT-urography is used only in patients with macroscopic hematuria and with no previous cystoscopy. We agree with the authors that this “the bladder-wall phase” (scans at 60 or 70 seconds after intravenous injection of contrast), allows the detection of small bladder tumors. However, we need to keep in mind that this additional phase cause significant increase in the effective radiation dose to the patients (18 to 25 mGy). For this reason, this protocol should be used with caution and primarily in older patients with macroscopic hematuria and absence of previous cystoscopy.

Reference

1. Kim JK, Park SY, Ahn HJ, Kim CS, Cho KS: Bladder cancer: analysis of multi-detector row helical CT enhancement pattern and accuracy in tumor detection and perivesical staging. Radiology. 2004; 231: 725-31.

Dr. Adilson Prando
Chief, Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: aprando@mpc.com.br