Combined Ultrasmall Superparamagnetic Particles of Iron Oxide–Enhanced and Diffusion-Weighted Magnetic Resonance Imaging Reliably Detect Pelvic Lymph Node Metastases in Normal-Sized Nodes of Bladder and Prostate Cancer Patients

BackgroundLymph node staging of bladder or prostate cancer using conventional imaging is limited. Newer approaches such as ultrasmall superparamagnetic particles of iron oxide (USPIO) and diffusion-weighted magnetic resonance imaging (DW-MRI) have inconsistent diagnostic accuracy and are difficult to interpret.ObjectiveTo assess whether combined USPIO and DW-MRI (USPIO–DW-MRI) improves staging of normal-sized lymph nodes in bladder and/or prostate cancer patients.Design, setting, and participantsTwenty-one consecutive patients with bladder and/or prostate cancer were enrolled between May and October 2008. One patient was excluded secondary to bone metastases detected on DW-MRI with subsequent abstention from surgery.InterventionPatients preoperatively underwent 3-T MRI before and after administration of lymphotropic USPIO using conventional MRI sequences combined with DW-MRI. Surgery consisted of extended pelvic lymphadenectomy and resection of primary tumors.MeasurementsDiagnostic accuracies of the new combined USPIO–DW-MRI approach compared with the “classic” reading method evaluating USPIO images without and with DW-MRI versus histopathology were evaluated. Duration of the two reading methods was noted for each patient.Results and limitationsDiagnostic accuracy (90% per patient or per pelvic side) was comparable for the classic and the USPIO–DW-MRI reading method, while time of analysis with 80 min (range 45–180 min) for the classic and 13 min (range 5–90 min) for the USPIO–DW-MRI method was significantly shorter (p < 0.0001). Interobserver agreement (three blinded readers) was high with a kappa value of 0.75 and 0.84, respectively. Histopathological analysis showed metastases in 26 of 802 analyzed lymph nodes (3.2%). Of these, 24 nodes (92%) were correctly diagnosed as positive on USPIO–DW-MRI. In two patients, one micrometastasis each (1.0 × 0.2 mm; 0.7 × 0.4 mm) was missed in all imaging studies.ConclusionsUSPIO–DW-MRI is a fast and accurate method for detecting pelvic lymph node metastases, even in normal-sized nodes of bladder or prostate cancer patients.