IMAGING

Organ-confined prostate cancer: effect of prior transrectal biopsy on endorectal MRI and MR spectroscopic imaging
Qayyum A, Coakley FV, Lu Y, Olpin JD, Wu L, Yeh BM, Carroll PR, Kurhanewicz J
Department of Radiology, University of California, San Francisco, San Francisco, CA, USA
AJR Am J Roentgenol. 2004; 183: 1079-83

• Objective: Our aim was to determine the effect of prior transrectal biopsy on endorectal MRI and MR spectroscopic imaging findings in patients with organ-confined prostate cancer.
• Materials and Methods: Endorectal MRI and MR spectroscopic imaging were performed in 43 patients with biopsy-proven prostate cancer before radical prostatectomy confirming organ-confined disease. For each sextant, two independent reviewers scored the degree of hemorrhage on a scale from 1 to 5 and recorded the presence or absence of capsular irregularity. A spectroscopist recorded the number of spectrally degraded voxels in the peripheral zone. The outcome variables of capsular irregularity and spectral degradation were correlated with the predictor variables of time from biopsy and degree of hemorrhage after biopsy.
• Results: Capsular irregularity was unrelated to time from biopsy or to degree of hemorrhage. Spectral degradation was inversely related to time from biopsy (p < 0.01); the mean percentage of degraded peripheral zone voxels was 18.5% within 8 weeks of biopsy compared with 7% after 8 weeks. Spectral degradation was unrelated to the degree of hemorrhage.
• Conclusion: In organ-confined prostate cancer, capsular irregularity can be seen at any time after biopsy and is independent of the degree of hemorrhage, whereas spectral degradation is seen predominantly in the first 8 weeks after biopsy. MRI staging criteria and guidelines for scheduling studies after biopsy may require appropriate modification.
  
  
• Editorial Comment
  This study provides several important information related to the performance and interpretation of endorectal MR and MR spectroscopic imaging of the prostate after transrectal biopsy. As we know a thickened and irregular prostate capsule is an important MRI sign of extra-prostatic tumor extension. The authors suggests that these capsular changes are common in organ-confined prostate cancer and are unrelated to time from biopsy and extent of post-biopsy hemorrhage and that these changes may represent a normal variant rather than a biopsy artifact. Another interesting finding was related to the presence of spectral degradation on MR spectroscopic studies. This spectral curve degradation was significantly more frequent within the first 8 weeks after transrectal biopsy and was caused by post-biopsy changes. It is well known that post- biopsy hemorrhage usually precludes an optimal result in the conventional endorectal MRI study performed for local staging of prostate cancer. Since post-biopsy changes precludes also an optimal spectroscopic evaluation of the metabolites, the authors recommend that a period of 8 weeks after biopsy is necessary before submit the patient to a MRI and MR spectroscopic evaluation. This information is very important because recent studies have shown that the ideal MRI protocol for local staging of prostate cancer is obtained with the association of conventional endorectal MRI and 3D-MR-spectroscopic techniques. 3D-MR-spectroscopic imaging offers important additional information to the conventional endorectal MRI exam such as: estimative of tumor volume, better prediction of an extra-prostatic disease and information about tumor aggressiveness. As the authors pointed out, this optimized post-biopsy interval for an adequate MRI and MR spectroscopic imaging should be balanced against patient anxiety, although this interval is probably negligible in terms of the natural history of prostate cancer.

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