IMAGING

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

• Purpose: To prospectively evaluate the accuracy of transrectal ultrasonography (US)-guided biopsy directed with magnetic resonance (MR) spectroscopic imaging in patients with an elevated prostate specific antigen (PSA) level and negative findings at prior biopsy by using subsequent biopsy results as the reference standard.
• Materials and Methods: The committee on human research approved this study, and written informed consent was obtained. MR imaging and MR spectroscopic imaging were performed in 42 men (age range, 45-75 years; average age, 63.3 years; median age, 65 years) with negative findings at two or more prostatic biopsies and at digital rectal examination. MR spectroscopic data were rated on a scale of 1 (benign) to 5 (malignant) on the basis of standardized metabolic criteria. Abnormal voxels were overlaid on the corresponding transverse transrectal US images and used to perform voxel-guided biopsy of the prostate. All patients subsequently received an extended-pattern biopsy scheme.
• Results: Thirty-one of 42 patients demonstrated metabolic abnormalities that were suspicious for cancer (voxels with scores > or = 4). Eleven patients with negative MR spectroscopic imaging results also had negative biopsy findings. Cancer was detected in 17 (55%) of 31 men with positive MR spectroscopic imaging findings (voxels with scores > or = 4) with a sensitivity of 100%, specificity of 44%, positive predictive value of 55%, negative predictive value of 100%, and accuracy of 67%. In men with at least one spectroscopic voxel with a score of 5 (12 of 17 men), the sensitivity, specificity, positive and negative predictive values, and accuracy were 71%, 84%, 75%, 81%, and 79%, respectively.
• Conclusion: Metabolic data from MR spectroscopic imaging can be transferred to transrectal US images and used to sample regions of cancer in men with rising PSA levels and negative findings at prior biopsy with good accuracy.
  
  
• Editorial Comment
  Despite new biopsy strategies with increased number of cores, many men find themselves in the clinical dilemma of having an elevated or rising PSA level and at least one prostatic biopsy with negative findings. MR spectroscopy is a new technology useful in the evaluation of prostate cancer (localization of cancer to a sextant of the prostate, the estimation of extracapsular extension and the assessment of its aggressiveness). Specifically, MR spectra from regions of prostate cancer show a significant reduction or absence of citrate and polyamines, while the choline level is elevated relative to the creatine level, thus resulting in significant changes in the choline-plus-creatine-to-citrate ratio in regions of cancer (grade IV, above 0.61 and grade V, above 0.86). We performed MR imaging and MR spectroscopic imaging in 42 men with negative findings at 2 or more prostatic biopsies and at digital rectal examination. The authors developed a method of overlaying the abnormal voxels (grade IV and V), detected on MR spectroscopic imaging, on the corresponding transverse transrectal US images and used to perform voxel-guided biopsy of the prostate. In this method, internal and external anatomic landmarks were used. All patients subsequently received an extended-pattern biopsy scheme. Cancer was detected in 17 (55%) of 31 men with positive MR spectroscopic imaging findings. Combination of the extended-pattern biopsy and MR spectroscopic imaging-guided biopsy results yielded a sensitivity of 85%, specificity of 89%, positive predictive value of 58%, negative predictive value of 97%, and accuracy of 89% (p < 0.5). These initial results show that radiologists who perform MR imaging, MR spectroscopic imaging examinations, and transrectal US-guided biopsy can transfer metabolic data from MR spectroscopic imaging to transrectal US images and effective use this data to sample regions suspicious of cancer in men with rising PSA levels and prior negative findings at biopsy. The authors found several important additional findings in this study: a) the average prostate volume in patients with cancer was higher than that in patients without cancer (87g vs. 58g, respectively). Five of 13 patients with positive biopsy findings had very large prostates (> 75g); b) in the 17 patients in whom cancer was detected with MR spectroscopic imaging and confirmed at biopsy, 10 (59%) had at least one site of cancer located toward the midline of the peripheral zone (area usually not sampled in most transrectal ultrasound biopsy scheme). This study has however several limitations. First, the accuracy with MR spectroscopic imaging reflects only a prediction of biopsy results, second, the authors did not evaluate the transition zone and third the transfer of spectral abnormalities onto the transrectal US images used for prostate biopsies is currently a manual process that is susceptible to localization errors. We think that MR spectroscopic imaging of the prostate is useful in patients with elevated PSA and with 2 sets of negative biopsies (one of which include the transition zone). To validate this hypothesis, however, a larger number of patients must be studied with standardized MR spectroscopic techniques.

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