Ultrasmall superparamagnetic particles of iron oxide allow for the detection of metastases in normal sized pelvic lymph nodes of patients with bladder and/or prostate cancer

Aim: Lymph node metastases influence prognosis and outcome in patients with bladder and prostate cancer. Cross sectional imaging criteria are limited in detecting metastases in normal sized lymph nodes. This prospective study assessed the diagnostic accuracy of ultrasmall superparamagnetic particles of iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI) for the detection of metastases in normal sized lymph nodes using extended pelvic lymph node dissection (ePLND) and histopathology as the reference standard. Methods: Seventy-five patients (bladder cancer, n = 19, prostate cancer n = 48, both, n = 8) were examined using 3T MR before and after USPIO-administration. A preoperative reading with two readers in consensus and a second postoperative reading with three independent blinded readers were performed. Results were correlated with histopathology and diagnostic accuracies were calculated for all readings. Results: A total of 2993 lymph nodes were examined histopathologically. Fifty-four metastatic nodes were found in 20/75 patients (26.7%). The first reading had a sensitivity of 55.0%, specificity of 85.5%, positive predictive value (PPV) of 57.9%, negative predictive value (NPV) of 83.9%, and diagnostic accuracy (DA) of 77.3% on a per patient level. The second reading had a mean sensitivity of 58.3%, specificity of 83.0%, PPV of 58.0%, NPV of 84.4% and DA of 76.4% on a per patient level. The majority of missed metastases were smaller than 5 mm in short axis diameter. Conclusions: USPIO-enhanced MRI in bladder and prostate cancer patients allows detection of metastases in normal sized lymph nodes and might guide the surgeon to remove suspicious lymph nodes not included in standard PLND.