Diffusion-weighted imaging for differentiating benign from malignant skull lesions and correlation with cell density

The objective of our study was to determine the utility of diffusion-weighted imaging (DWI) and cell density for differentiating benign from malignant skull lesions.

A retrospective review was performed. Minimum apparent diffusion coefficient (ADC) values were measured and normalized to white matter, which we refer to as "normalized ADC," in 24 skull lesions (12 malignant and 12 benign) in 18 patients. In addition, cell densities were measured in 15 cases and correlated with ADC values.

The average minimum ADC in malignant tumors was 0.70 × 10(-3) mm(2)/s versus 1.11 × 10(-3) mm(2)/s in benign tumors (p = 0.0037). Similarly, the average normalized ADC for malignant tumors was 1.03, whereas the average normalized ADC for benign tumors was 1.65 (p = 0.0012). Receiver operating characteristic curve analysis yielded optimal normalized ADC and ADC thresholds of 1.23 (accuracy, 84.6%; sensitivity, 75.0%; specificity, 92.3%) and 1.01 × 10(-3) mm(2)/s (accuracy, 83.7%; sensitivity, 83.3%; specificity, 84.6%), respectively. There was a significant inverse correlation between cell density and normalized ADC (r = -0.58; p = 0.023). The low cellularity in chordoma and low-grade chondrosarcoma and high cellularity in eosinophilic granuloma may explain the DWI features of these lesions.

ADC values in skull lesions correlate with cell density and can potentially narrow the differential diagnoses for indeterminate skull lesions. Understanding the histopathologic features of skull lesions can refine interpretation of DWI.