Preoperative evaluation of pelvine lymph node metastasis in high risk prostate cancer with intravoxel incoherent motion (IVIM) MRI.

Objectives: To evaluate benign and malignant pelvine lymph nodes in prostate cancer patients with biexponential intravoxel incoherent motion (IVIM) MRI of the prostate prior to radical prostatectomy.

Methods: The ethics committee approved this retrospective study with waiver of informed consent. From February 2012 to November 2013 43 patients with histopathologically proven prostatic cancer were included. All patients were examined applying a standardized MRI protocol including IVIM diffusion weighted imaging with multiple b-values ranging from 0 to 950 s/mm². MR imaging was performed one day prior to radical prostatectomy. Thereafter, extended lymph node resection was performed. For each MRI all visible lymph nodes were registered and calculated as individual regions of interest. These findings were correlated with postoperative pathology. The apparent diffusion coefficient ADC, the diffusion coefficient D and the perfusion fraction f were calculated from IVIM DWI using a biexponential fit.

Results: A total of 120 lymph nodes were detected on MRI. 95 of these were determined as benign and 25 as malignant. The average ADC was significantly lower in malignant compared to benign lymph nodes (0.88 × 10 vs 1.67 × 10 mm²/s, p < 0.001). Likewise, the average diffusion coefficient D was significantly lower in lymph node metastasis (0.54 × 10 vs 1.10 × 10 mm²/s, p < .001). The signal rate due to perfusion was significantly higher in malignant compared to benign nodes (33.4% vs. 27.1%, p = 0.02).

Conclusions: Applying biexponential IVIM MRI demonstrates significant differences in diffusion parameters ADC and D, as well as in the perfusion fraction f for benign and malignant lymph nodes. Therefore, IVIM might help to further improve the preoperative assessment of lymph nodes in MRI.