Whole-body diffusion-weighted imaging: is it all we need for detecting metastases in melanoma patients?

To investigate whether whole-body diffusion-weighted imaging (WB-DWI) alone is adequate for detecting metastases in melanoma patients, or if standard WB contrast-enhanced magnetic resonance imaging (WB-ceMRI) is required.

Seventy-one WB-DWI studies were performed quarterly along with whole-body MRI including contrast-enhanced sequences (WB-ceMRI) in 19 patients with advanced melanoma. The reference standard was biopsy, other imaging investigations, or changes observed on follow-up. Findings of metastasis in separate WB-DWI and WB-DWI + WB-ceMRI readings were compared using κ statistics. Additionally, the distribution of findings was examined and calculated per body region (brain, neck, chest, abdomen, liver, pelvis, subcutaneous tissues, bones) and diagnostic accuracy (DA), sensitivity, specificity, negative predictive value, and positive predictive value were calculated per patient.

The eight examinations that were positive by the reference standard contained a total of 14 metastatic findings. With almost perfect agreement between techniques (κ = 85 %, 95 % CI 70-100 %) for detection of examinations with metastatic findings, and complete agreement in extracranial metastasis detection, 10 metastases were detected using WB-DWI and 13 using WB-DWI + WB-ceMRI. WB-DWI and WB-DWI + WB-MRI had equivalent per patient DA (79 %).

WB-DWI without additional WB-ceMRI sequences is promising for the detection of extracranial metastases in melanoma patients, but contrast-enhanced MRI is required for evaluating the brain.