Routine pelvic MRI using phased-array coil for detection of extraprostatic tumour extension: accuracy and clinical significance

OBJECTIVES: To determine the accuracy and assess the clinical significance of surface-coil 1.5-T magnetic resonance imaging (MRI) for the detection of locally advanced prostate cancer (PCa). METHODS: Between December 2007 and January 2010, we examined 209 PCa patients (mean age = 62.5 years) who were consecutively treated with robot-assisted laparoscopic prostatectomy and prospectively staged by MRI. One hundred and thirty-five patients (64.6 %) had locally advanced disease. Conventional clinical tumour stage and MRI-assessed tumour stage were compared with histopathological tumour stage (pT). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and overall accuracy (OA) were calculated using pT as the “gold standard”. Overstaged and understaged cases at MRI were reviewed. RESULTS: Sensitivity, specificity, PPV, NPV and OA for the detection of locally advanced disease were 25.9, 95.9, 92.1, 41.2 and 50.5 % and 56.3, 82.2, 85.4, 50.4 and 65.4 % for clinical staging and MRI, respectively. Among patients understaged at MRI, the resection margins were free in 64.4 % of the cases (38/59). CONCLUSIONS: Although the accuracy was limited, the detection of locally advanced disease improved substantially when MRI was added to routine clinical staging. The majority of the understaged patients nevertheless achieved free margins. When assessing the clinical significance of MRI staging the extent of extraprostatic extension has to be considered. KEY POINTS: • MRI substantially improves detection of locally advanced prostate cancer • MRI has limited overall staging accuracy • Most T3 cancers unrecognised at MRI still achieved free resection margins • Assessing the true clinical contribution of MRI remains challenging