Imaging

UROLOGICAL SURVEY

Takeuchi M, Sasaki S, Ito M, Okada S, Takahashi S, Kawai T, Suzuki K, Oshima H, Hara M, Shibamoto Y

Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan

Radiology. 2009; 251: 112-21

PURPOSE: To prospectively evaluate the ability of diffusion-weighted (DW) magnetic resonance (MR) imaging to be used to determine the T stage of bladder cancer and to measure the correlation between the apparent diffusion coefficient (ADC) and histologic grade.

MATERIAL AND METHODS: This study was approved by the local institutional review board. All patients gave written informed consent. Forty patients with a total of 52 bladder tumors underwent MR imaging that included DW imaging. Histologic grade was determined for all tumors. Two radiologists interpreted four image sets (ie, T2-weighted images alone, T2-weighted plus DW images, T2-weighted plus dynamic contrast agent-enhanced images, all three image types together). Conventional criteria were used for interpreting T2-weighted and contrast-enhanced images. For DW images, new staging criterion developed on the basis of the hypothesis that tumors, submucosal tissue, and muscles show high, low, and intermediate signal intensity, respectively, was used. The McNemar test was used to examine differences in accuracy, sensitivity, and specificity. Differences in the performance were analyzed by comparing the areas under the receiver operating characteristic curves (A(z) values). To compare ADCs between three histologic grades, analysis of variance was used.

RESULTS: The overall accuracy of T stage diagnosis was 67% for T2-weighted images alone, 88% for T2-weighted plus DW images, 79% for T2-weighted plus contrast-enhanced images, and 92% for all three image types together. The overall accuracy, specificity, and A(z) for diagnosing T2 or higher stages were significantly improved by adding DW images (P < .01). The mean ADC of G3 tumors was significantly lower than that of G1 and G2 tumors (P < .01).

CONCLUSION: DW images provided useful information for evaluating the T stage of bladder cancer, particularly in differentiating T1 or lower tumors from T2 or higher tumors. The ADC may in part predict the histologic grade of bladder cancer.

Editorial Comment

Local staging of bladder cancer can be performed either by CT or by MRI. Sensitivity and specificity for detecting perivesical invasion with multidetector CT are 92% and 98% respectively, with an accuracy of 96%. These results are obtained, if MDCT is performed more than 7 days after biopsy (1).

The high intrinsic contrast of MR imaging permits distinction of bladder wall layers (2). With fast dynamic contrast-enhanced imaging, bladder cancer enhances more intense and earlier than normal bladder wall and post biopsy changes. This characteristic enhancement may allow differentiation of tumor from fibrosis or edema, although this is still difficult soon after transurethral resection. MR imaging has a reported staging accuracy of 72%-96% and is superior to CT for differentiation of superficial versus deep muscle invasion, unfortunately, overstaging occurs in about 20% patients.

Although based on relative small series, the authors present interesting results showing that diffusion-weighted imaging (DWI) may significantly reduce overstaging of bladder cancer observed with conventional MRI techniques. This sequence is relatively fast and easy to accomplish and can be performed routinely. Radiologists should include DWI in the protocol of MRI staging of bladder cancer. Further studies are warranted to confirm that this sequence has higher accuracy than conventional sequences (T2-weighted images + fast dynamic contrast enhanced), for the demonstration of invasion of perivesical tissues. Another potential utility of this sequence would be its ability to differentiate scars and reactive tissue after biopsy from tumor tissue.

Dr. Adilson Prando

Chief, Department of Radiology and

Diagnostic Imaging, Vera Cruz Hospital

Campinas, São Paulo, Brazil

E-mail: [e-mail]

• 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.
• 2. Barentsz JO, Witjes JA, Ruijs JH: What is new in bladder cancer imaging. Urol Clin North Am. 1997; 24: 583-602.
• 3. Watanabe H, Kanematsu M, Kondo H, Goshima S, Tsuge Y, Onozuka M, et al.: Preoperative T staging of urinary bladder cancer: does diffusion-weighted MRI have supplementary value? AJR Am J Roentgenol. 2009; 192: 1361-6.

Imaging

Urinary bladder cancer: diffusion-weighted MR imaging--accuracy for diagnosing T stage and estimating histologic grade

Publication Dates

• Publication in this collection
  24 Aug 2009
• Date of issue
  June 2009