Possible pathological basis for false diagnoses of lymph nodes by USPIO-enhanced MRI in rabbits.

PURPOSE

To determine the cause of misdiagnosis of lymph nodes in ultrasmall superparamagnetic iron oxide (USPIO) enhanced magnetic resonance imaging (MRI) using histological findings in rabbit tumor and inflammatory models.

MATERIALS AND METHODS

Thirty-six rabbits were randomly divided into inflammatory and tumor groups. MRI of the popliteal fossa was performed before and 24 hours after USPIO administration. Diagnoses of popliteal lymph nodes were evaluated based on dedicated criteria and were compared with histological and electronic microscopic findings.

RESULTS

There were 46 inflammatory and 26 metastatic lymph nodes. Sensitivity, specificity, and positive and negative predictive values of the diagnosis of nodal metastasis were 84.6%, 87.0%, 78.6%, and 90.9%, respectively. There were four false-negatives with subcapsular metastatic foci and six false-positives with predominant cortex and paracortex hyperplasia. Electron microscopy showed that in inflammatory nodes, cytophagic bubbles contain many USPIO particles, while in metastatic nodes they contained predominantly cellular residues.

CONCLUSION

Diagnosis of lymph node malignancy is largely determined by the location and number of metastatic tumor cells. A profound understanding of the physiological role of macrophages in nodes with tumor burden will contribute to better diagnoses for clinical application.