IMAGING

Conventional MRI Capabilities in the Diagnosis of Prostate Cancer in the Transition Zone
Li H, Sugimura K, Kaji Y, Kitamura Y, Fujii M, Hara I, Tachibana M
Department of Radiology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan
AJR Am J Roentgenol. 2006; 186: 729-42

• Objectives: Our objectives were to evaluate the diagnostic capabilities of conventional MRI for the accurate detection of prostate cancer within the transition zone and to compare the results with histopathologic examination results.
• Materials and Methods: One hundred sixteen prostate specimens with prostate cancer were consecutively obtained. Axial, sagittal, and coronal T2- and T1-weighted MR images with gadopentetate dimeglumine were independently reviewed by two radiologists. The diagnostic base criteria of the MR images were determined for detecting transition zone cancer as follows: lesions with A, uniform low intensity on T2-weighted images; B, homogeneous gadolinium enhancement; and C, irregular margins both on gadolinium-enhanced and T2-weighted images. Wilcoxon’s rank sum and chi-square tests and receiver operating characteristic curves were used. Differences of less than 0.05 were considered significant.
• Results: Eighty-six lesions in the transition zone were analyzed. Histopathologic analysis showed 53 cancers and 33 benign lesions. The diagnostic sensitivity, specificity, and accuracy for cancer were 50%, 51%, and 51%, respectively with criteria A; 68%, 75%, and 71% with criteria B; and 60%, 72%, and 65% with criteria C. When base criteria were combined into criteria A-B, A-C, and B-C and then further divided into three subgroups, accuracy was found to be highest when the lesion satisfied any two criteria from A, B, and C than those of base criteria, combination criteria, and the other two subgroups.
• Conclusion: The addition of gadolinium-enhanced MRI to T2-weighted imaging provides better accuracy for detecting cancerous transition zone lesions than the use of T2-weighted imaging alone.
  
  
• Editorial Comment
  Radical prostatectomy studies have demonstrated that 75-85% of cancers arise in the peripheral zone, but up to 25% prostate cancer occurs within the transition zone. Endorectal MR imaging is a useful modality in the detection of the peripheral zone cancers. This technique is able to detect 67-76% of peripheral cancer demonstrated by step-section histopathologic studies but has limitations in the demonstration of cancer in the transition zone. This limitation occurs because the transition zone appears usually as a very heterogeneous region on T2-weighted images due to the presence of nodular hyperplastic changes. Previous studies have suggested some MR imaging features found in transition zone cancer: homogeneous hypointense lesion on T2-weighted images with ill-defined margins and lack of capsule .The authors of this study demonstrates that conventional MR imaging, without the use of an endorectal coil, can be useful for the detection of transition prostate cancer. They added new imaging criteria: homogeneous enhancement and presence of irregular margins .If these additional findings are used, the specificity rates for the detection of transition zone cancer could be increased from 51% to 82%. In the last 2 years, we have been using routinely, in our institution, endorectal MR imaging and spectroscopy for the detection of prostate cancer arising in the transition zone. We have found that diffusion weighted images and the evaluation of the kinetics of gadolinium enhancement by the lesion can be of further value. Thus the, presence of a nodule with ill-defined margins, homogeneous hypointensity on T2 weighted images, with hypointensity on diffusion weighted images and fast contrast enhancement (“wash-in”) and fast contrast de-enhancement(“wash-out”), is very suggestive of transition zone cancer. Spectroscopy shows only high levels of choline particularly in larger tumors and thus can also be of some value.

Dr. Adilson Prando
Chief, Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil