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IMAGING
Urinary
bladder cancer: diffusion-weighted MR imaging--accuracy for diagnosing
T stage and estimating histologic grade
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.
- Materials
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.
References
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.
Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging, Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: adilson.prando@gmail.com
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