PURPOSE: To determine whether chronic prostatitis affects three-dimensional proton magnetic resonance (MR) spectroscopic imaging in evaluation of disease in the peripheral zone. MATERIALS AND METHODS: Combined MR imaging and three-dimensional MR spectroscopic imaging data were examined retrospectively in 12 patients with radical prostatectomy specimens that contained regions of chronic prostatitis larger than 6 mm in the peripheral zone. The 6-mm restriction was based on MR spectroscopic imaging spatial resolution of 6.25 mm. Transverse T2-weighted MR images were reviewed for changes in signal intensity (SI): normal, suspicious for cancer (nodular focal low SI), or indeterminate (focal low SI that was not nodular or contour deforming or diffuse low SI). At MR spectroscopic imaging, proton spectra were considered suspicious for cancer if the ratio of choline plus creatine to citrate was more than 2 SDs above normal mean peripheral zone values. RESULTS: In the 12 patients, mean pretreatment prostate-specific antigen level was 5.77 +/- 2.07 (SD), and median biopsy Gleason score for the gland was 6. At MR imaging in the area of histopathologically confirmed chronic prostatitis, seven of 12 patients had focal low SI that was not nodular (contour deforming) over a region in and around the pathologically defined focus of chronic prostatitis. MR imaging in one patient showed diffuse low SI that correlated with a diffuse area of chronic prostatitis at pathologic examination. MR imaging in another patient showed nodular focal low SI that was suspicious for cancer and corresponded to a focus of chronic prostatitis at pathologic examination. The remaining three patients had no MR imaging abnormality in the region of chronic prostatitis. In the pathologically identified regions of chronic prostatitis, MR spectroscopic imaging data in nine of 12 patients demonstrated elevated choline peak and reduced or no citrate, findings that mimic those of cancer. In two patients, the spectra were normal, and in the remaining patient, the spectra were nondiagnostic. CONCLUSION: At MR spectroscopic imaging, pathologically confirmed chronic prostatitis may demonstrate metabolic abnormality that leads to false-positive diagnosis of cancer. The most common MR imaging finding in chronic prostatitis was focal low SI that was not specific for cancer. In one patient, the MR imaging diagnosis of cancer could not be excluded.
