Diffusion-weighted MRI sensitive for metastasis in pelvic lymph nodes

1.Diffusion-weighted magnetic resonance imaging (DWMRI)  was shown to be both sensitive and specific for identification of pelvic lymph node metastases among patients with prostate or bladder cancer. 

2. The inclusion of several additional imaging criteria in conjunction with DWMRI reduced the number of diagnostic errors and was associated with superior sensitivity relative to DWMRI alone. 

Evidence Rating Level: 2 (Good) 

Study Rundown: The presence of metastasis to local lymph nodes alters cancer staging and may influence treatment decisions. The current protocol for the evaluation of lymph node metastasis involves preoperative imaging with either computed tomography (CT) or magnetic resonance imaging (MRI), which detect lymph nodes primarily based on size. These techniques are currently limited by their insensitivity to smaller lymph nodes containing metastases, and may yield falsely positive results in hypertrophic lymph nodes. DWMRI represents a promising alternative detection method, as it is very sensitive to the subtle changes caused by invasion from cancer cells.

In the present study, the performance of DWMRI in the identification of lymph node metastasis was evaluated among patients with prostate or bladder cancer. Using histopathologic evaluation as the reference standard, DWMRI showed a high sensitivity and specificity. The study’s primary limitation was its single-institution design, and further work is necessary to replicate these findings at other medical centers.

Click to read the study in Radiology

Relevant Reading: Noninvasive detection of clinically occult lymph-node metastases in prostate cancer

In-Depth [nonrandomized clinical trial]: The study enrolled 120 consecutive patients at a single institution with bladder or prostate cancer who had been previously staged as having no metastases (N0) by conventional preoperative cross-sectional imaging (CT and/or MRI). All enrolled patients underwent DWMRI at 3.0 Tesla to evaluate for previously-unidentified pelvic lymph node metastases. Images were reviewed both pre- and postoperatively, as well as in conjunction with standard MRI for the evaluation of several prespecified imaging criteria (e.g. lymph node shape). All patients subsequently underwent tumor resection with extended pelvic lymph node dissection. Imaging results were compared to histopathologic examination of removed lymph nodes for the diagnosis of metastasis. In total, 33 patients (27.5%) had histologically-confirmed metastasis in 88 lymph nodes. Using DWMRI,  metastasis was correctly identified in 24/33 patients, yielding an overall sensitivity, specificity, and diagnostic accuracy of 72.7%, 86.2%, and 82.5%, respectively. Most false negative examinations were in very small nodes, less than 5 millimeters in diameter. Following incorporation of the additional MRI-based imaging criteria into lymph node assessment, sensitivity increased to 94.5%.

Image: PD

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