IMAGING

Transition Zone Prostate Cancers: Features, Detection, Localization, and Staging at Endorectal MR Imaging
Akin O, Sala E, Moskowitz CS, Kuroiwa K, Ishill NM, Pucar D, Scardino PT, Hricak H
Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
Radiology. 2006; 239: 784-92

• Purpose: To retrospectively evaluate the accuracy of endorectal magnetic resonance (MR) imaging in the detection and local staging of transition zone prostate cancers, with pathologic analysis serving as the reference standard, and to assess MR imaging features of these cancers.
• Materials and Methods: The institutional review board approved this HIPAA-compliant retrospective study and waived the informed consent requirement. An institutional database of 986 patients who underwent MR imaging before radical prostatectomy yielded 148 consecutive patients with at least one transition zone cancer at step-section pathologic analysis. An additional 46 patients without transition zone cancer were randomly selected as a control group. Two readers independently reviewed MR studies to identify patients with transition zone cancers and determine the location and local extent of these cancers. Imaging features that helped in the identification of transition zone cancers were recorded. Descriptive and kappa statistics, as well as receiver operating characteristic and multivariate logistic regression analyses, were used.
• Results: For identification of patients with transition zone cancers, sensitivity and specificity were 75% and 87%, respectively, for reader 1 and 80% and 78%, respectively, for reader 2. Interreader agreement was fair. For detection of the location of transition zone cancer, the area under the receiver operating characteristic curve was 0.75 for reader 1 and 0.73 for reader 2. Interreader agreement was fair. The readers’ accuracy in detecting transition zone cancer foci increased significantly (P=.001) as tumor volume increased. In the detection of extraprostatic extension of transition zone cancers, sensitivity and specificity were 56% and 94%, respectively, for reader 1 and 28% and 93%, respectively, for reader 2. Homogeneous low T2 signal intensity (P=.001 for reader 1, P<.001 for reader 2) and lenticular shape (P=.017 for reader 1) were significantly associated with the presence of transition zone cancer.
• Conclusion: MR imaging can be used to detect, localize, and stage transition zone prostate cancers.
  
  
• Editorial Comment
  Recently some reports have been shown the role of MR imaging in the assessment of transition zone (TZ) cancers. MR features observed in transition zone cancer are presence of nodule with ill-defined margins (lack of capsule) showing homogeneous hypo intensity on T2 weighted images. In this retrospective study, the authors added two other important features that helped in the identification of TZ cancers: lenticular shape of the lesion and invasion of the anterior fibromuscular stroma. Although none of these findings is pathognomonic for transition zone cancer the authors found that the combination of these features allows the identification of these cancers with specificity ranging from 78 to 87%. The authors observed that, tumor volume was an important factor in the detection of TZ cancers. The accuracy of TZ cancer detection at MR imaging was related to the transition zone cancer volume, with higher accuracy for cancers with larger volumes. The accuracy was significantly higher for tumor volume greater than or equal 0.77 mL. This may not be relevant if we consider that patients with TZ cancers have higher tumor volumes than patients with peripheral zone cancers. Although based on small series, another important and original observation of the current study is that local staging of transition zone cancers is possible with MR imaging and that extraprostatic extension occurs at a larger mean tumor volume in TZ cancers than in peripheral zone cancers. As we have mentioned in the March – April 2006 issue of this journal, other MR imaging techniques such as diffusion-weighted images, contrast material–enhanced MR imaging and MR spectroscopic imaging can also be used for evaluation of TZ cancers. In our experience, the findings on conventional MR imaging should be associated with these other imaging techniques.

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