Wednesday, 5 August 2015

xrayoftheweek 31: identifying high risk rectal cancers

This week's #xrayoftheweek is another panel of MRI (and one CT) images (of the rectum and liver), illustrating the importance of accurate reporting and the emergence of data which allows us to stratify rectal cancer into low and high risk groups.

a = coronal MRI showing rectal cancer and tumour signal tissue extending into a large vessel

b = coronal CT showing rectal cancer and tumour density tissue extending into a large vessel

c & e = diffusion weighted image (b=1000) showing rounded high signal lesion in liver

d & f = ADC map showing low signal in lesions seen on c & e respectively, indicating restricted diffusion and liver metastases

There is a growing body of research into the stratification of rectal cancers into low and high risk, based on pre-treatment MRI. Factors such as stage greater than or equal to T3, nodal involvement, and the presence of extramural venous invasion (EMVI), have all been shown to be associated with a "higher risk" and synchronous metastatic disease. 

Of these, EMVI is emerging as a key predictor of liver metastases, either synchronously or within 24 months of diagnosis. It is identified by the presence of tumour signal tissue extending into, filling and expanding a vessel adjacent to the tumour itself. It is best seen on a coronal image. This #xrayoftheweek image shows EMVI on both MRI and CT, and synchronous liver metastases which are shown as restricted diffusion lesions. In the future, such stratification of rectal cancers (even if liver metastases aren't seen at the time of initial staging) may direct patients to different therapeutic regimes taking into account their risk status.

For a recap of the basic signal changes and for links to further reading about diffusion weighted imaging, take a look at my previous xrayoftheweek post.

#FOAMed #FOAMrad

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