Diffusion-weighted MRI in detection of renal metastases.

To cite: Goyal A, Sharma R, Bhalla A, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2013201555 DESCRIPTION A 25-year-old man, diagnosed with primitive neuroectodermal tumour of the left tibia, presented with abdominal pain. His serum creatinine was 2.5 mg/dL. Sonography revealed multiple abdominal masses which warranted contrast-enhanced CT (CECT)/MRI for accurate disease assessment. However, considering the risk of contrast-induced nephropathy (with iodinated contrast in CECT) and nephrogenic systemic fibrosis (with gadolinium chelates in CE MRI), contrast was not administered. The patient underwent non-contrast MRI along with diffusion-weighted (DW) imaging on a 1.5 T scanner. Axial DW sequence was performed at b-values of 0, 500 and 1000 s/mm and apparent diffusion coefficient (ADC) maps for quantification of diffusion restriction were generated. Axial DW images at b 500 s/mm (figure 1A), b 1000 s/mm (figure 1B) and ADC map (figure 1C) clearly demonstrated bilateral multiple renal metastases showing marked restriction of diffusion of water molecules, attributable to high cellularity of primary tumour. Relative to conventional MRI sequences (figure 1D), the lesion-to-background contrast was significantly better in DW images, making these focal lesions much more conspicuous on DWMRI. DW MRI has been a part of our imaging protocol for renal lesions since 2008. It is an excellent means to demonstrate multiple renal metastases, which may not be so conspicuous on conventional CT/MRI. Moreover, additional lesions may be detected, and this may preclude surgical resection for apparently solitary lesions. The elegant display of multiple lesions against a suppressed background signal may substitute and even supersede CE imaging. DW MRI characterises tissues by detecting alterations in thermally induced Brownian motion of water molecules within them. The addition of DW imaging to routine abdominopelvic MRI protocols yields diagnostically helpful information with little increase in imaging time. Moreover, DW MRI may obviate the need for contrast administration, which is desirable since patients with focal renal lesions may have associated renal dysfunction.