(ChemotherapyAdvisor) –  Among patients with bladder and prostate cancer, magnetic resonance imaging (MRI) enhanced with ultrasmall superparamagnetic particles of iron oxide (USPIO) contrast agent, allows detection of lymph node metastases that are not detected in conventional imaging exams, according to a prospective study published in the European Journal of Cancer.

“Our results indicate that USPIO-enhanced MRI enables detection of lymph node metastases in normal sized lymph nodes in bladder and prostate cancer patients staged as metastasis free (N0) based on the conventional cross sectional imaging methods,” reported Harriet C. Thoeny, MD, of the Department of Radiology, Neuroradiology and Nuclear Medicine, at the Institute for Diagnostic, Interventional and Pediatric Radiology, Inselspital University Hospital Bern, in Bern, Switzerland, and her coauthors. “Despite the limited spatial resolution of MRI, we were even able to detect lymph node metastases smaller than 5 mm.”

A total of 2,993 lymph nodes from 75 patients with bladder cancer, prostate cancer, or both, were examined, first using a 3-telsa (3T) MRI before and after administration of USPIO contrast-enhancement agent, and subsequently histopathologically, to assess the accuracy of USPIO-enhanced MRI for detecting metastases.

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Metastatic lymph nodes (n=54) were identified with a diagnostic accuracy of 77.3%, sensitivity of 55% and specificity of 85.5%, the authors reported.

“The majority of missed metastases were smaller than 5 mm in short-axis diameter,” they cautioned. “Some anatomical regions were particularly difficult to evaluate for small (≤ 5 mm) metastases, including the perivesical and periprostatic area and lymph nodes along the common iliac vessels.”

Nevertheless, a total of 17 metastases of that size were correctly identified, they noted.

USPIO-enhanced MRI in bladder and prostate cancer patients “might guide the surgeon to remove suspicious lymph nodes not included in standard pelvic lymph node dissection,” the authors concluded. “Due to the still substantial number of false-negative readings, USPIO-enhanced MRI cannot replace extended pelvic lymph node dissection. However, we have demonstrated that USPIO-enhanced MRI provides valuable additional information which could guide the surgeon to extend the region of standard pelvic lymph node dissection.”