IMAGING

Diagnosis of Prostate Cancer in Patients with an Elevated Prostate-Specific Antigen Level: Role of Endorectal MRI and MR Spectroscopic Imaging
Costouros NG, Coakley FV, Westphalen AC, Qayyum A, Yeh BM, Joe BN, Kurhanewicz J
Department of Radiology, University of California, San Francisco, San Francisco, CA, USA
AJR Am J Roentgenol. 2007; 188: 812-6

• Objective: The objective of our study was to determine the accuracy of endorectal MRI and MR spectroscopic imaging (MRSI) in the diagnosis of prostate cancer in patients with an elevated serum prostate-specific antigen (PSA) level.
• Materials and Methods: We retrospectively identified 40 patients with an elevated serum PSA level and without a histologic diagnosis of prostate cancer who underwent endorectal MRI and MRSI at our institution. On the basis of MRI findings alone and then combined MRI and MRSI findings, a single experienced observer rated the presence or absence of prostate cancer in each side of the prostate on a 5-point scale (1 = definitely absent, 5 = definitely present). Areas under the receiver operating characteristic (ROC) curve were calculated using the hemiprostate as the unit of analysis. The presence or absence of cancer on subsequent endorectal sonographically guided sextant biopsy was used as the standard of reference.
• Results: Biopsy revealed no cancer in 24 patients, bilateral cancer in 11, and unilateral cancer in five. The areas under the ROC curve for the diagnosis of prostate cancer by hemigland was 0.70 for MRI alone and 0.63 for combined MRI and MRSI (no significant difference, p = 0.32).
• Conclusion: Endorectal MRI and MRSI are reasonably accurate for the diagnosis of prostate cancer in patients with an elevated serum PSA level, but the remaining limitations suggest that MRI and MRSI should be used as a supplement rather than a replacement for biopsy using the current technology and diagnostic criteria.
  
  
• Editorial Comment
  The authors present a retrospective study to determine if conventional and 3D-spectroscopic endorectal magnetic resonance imaging (3D-MRSI) techniques are accurate for the diagnosis of prostate cancer in patients with an elevated PSA. They had a 63% accuracy using conventional MRI and 3D-MRSI. Previous study on this subject has demonstrated an accuracy ranging from 67% to 79% (1). One important limitation of this study is related to the fact that the cancer was determined to be present or absent in each hemiprostate on the basis of the presence or absence of an ipsilateral positive biopsy result, on a subsequent endorectal sonographically guided biopsy. These biopsies were performed within 2 years of MRI and MRSI. In other words, the standard sextant sonographically guided biopsy was performed without the knowledge of the results obtained with the MRI and 3D-MRSI and was considered the standard of reference. In our institution the abnormal areas(areas with abnormal voxels), seen on 3D-MRSI are projected on the film containing the conventional axial T2 sequence, and external and internal prostate landmarks obtained from these images are used during transrectal ultrasound examination to adequate biopsy the areas containing the suspicious voxels. As we have already pointed out this process has limitation since is not an easy task, but allows an accuracy of 67% in patients with grade 4 (possible cancer) and accuracy of 79% in patients presenting at least one voxel grade 5 (cancer is definite present).
  Although the author’s conclusion is that addition of MRSI to MRI alone does not significantly improve the diagnostic accuracy for prostate cancer detection they also concluded that MRI and MRSI might still serve as a useful supplement to endorectal sonographically guided biopsy on an individual basis. A repeat biopsy could target regions that show an abnormality on MRI and MRSI to help improve the diagnostic yield of endorectal sonographically guided biopsy, as we have previously shown.

Reference
1. Prando A, Kurhanewicz J, Borges AP, Oliveira EM Jr, Figueiredo E: Prostatic biopsy directed with endorectal MR spectroscopic imaging findings in patients with elevated prostate specific antigen levels and prior negative biopsy findings: early experience. Radiology. 2005; 236: 903-10.

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