[Differentiation of axillary inflammatory and metastatic lymph nodes with diffusion-weighted imaging in animal modes]

To evaluate the value of diffusion-weighted imaging (DWI) in the differentiation of axillary inflammatory hyperplastic and metastatic lymph nodes.

Forty female New Zealand white rabbits were divided randomly into 2 groups (n = 20 each). And the animal models of axillary inflammatory hyperplastic and metastatic lymph nodes were established. All successfully implanted models received conventional magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) examinations. The features of signal intensity and shapes of lymph nodes were observed in two groups. The sizes of lymph nodes were measured on the selected axial T(2)WI. The signal intensity and appearance diffusion coefficient (ADC) value of lymph nodes and dorsal muscle at the same slice were measured on the selected T(2)WI, DWI and ADC map respectively. The relative signal intensity (rSIT(2)WI, rSIDWI) and relative ADC (rADC) value of lymph nodes to dorsal muscle were calculated and compared. The diagnostic efficacy of differentiating benign and malignant lymph nodes was analyzed with rADC value through the receiver operating characteristic curve. The correlation between rADC value and cell density was assessed with pathological findings as reference standard.

The differences of size, rSIT(2)WI and rSIDWI were not statistically significant between two groups. The rADC value of inflammatory lymph nodes was greater than that of metastatic lymph nodes (0.91 ± 0.14 vs 0.64 ± 0.18). Significant difference existed (t = 3.879, P = 0.03). But there was a little overlap between two groups. With 0.78 as the diagnostic threshold of rADC value, the sensibility and specificity was 86.2% and 74.4% respectively. The correlation between rADC value and cell density of inflammatory hyperplastic and metastatic lymph nodes was significantly inverse (r = -0.53, P = 0.003).

As compared with the routine MRI sequence, rADC value has a higher diagnostic efficacy in the differentiation of benign and malignant lymph nodes. Cell density may be the most important influencing factor for the differences of rADC value between two groups of lymph nodes.