FAILURE OF GADOPENTETATE DIMEGLUMINE-ENHANCED, HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING TO DIFFERENTIATE AMONG MELANIN-CONTAINING SKIN TUMORS

Rationale and Objectives. We evaluated the diagnostic potential of gad opentetate dimeglumine-enhanced, high-resolution magnetic resonance (M R) imaging to differentiate benign from malignant melanin-containing s kin tumors. Methods. Forty-five patients were prospectively examined u sing high-resolution MR imaging at 1.5 T using a 2.5-cm surface coil. For tumor assessment, T1-weighted and T2-weighted transverse spin-echo sequences were acquired. After intravenous administration of gadopent etate dimeglumine (0.1 mmol/ kg), the T1-weighted transverse sequence was repeated. Contrast enhancement was quantitatively determined as th e percentage increase of signal intensity. Histologic findings were co rrelated using the Wilcoxon signed-ranks test. The quality of contrast enhancement was assessed by three independent investigators who were unaware of the patients' history and histologic data. The signal-re-no ise ratio (SNR) was calculated in the T2-weighted sequence. Significan ce was rested using the Wilcoxon signed-ranks test. Results. In all tu mors, contrast enhancement was visually discernible. Half of the cases were enhanced inhomogeneously. The percentage of contrast enhancement did not correlate with histologic findings, Malignant melanomas could not be differentiated from benign melanocytic nevi with the use of ga dopentetate dimeglumine. Determination of the SNR in T2-weighted seque nces revealed no significant difference for histologic subgroups or tu mor type. Conclusion. Gadopentetate dimeglumine-enhanced MR imaging do es not differentiate malignant melanomas from benign melanocytic nevi. Determination of the SNR in the T2-weighted sequences revealed no sig nificant difference for histologic subgroups.