Radiation is the most common cause of non-traumatic brachial plexopathy and much of this is iatrogenic. Symptoms may be delayed for months to years with peak onset being 10-20 months. MRI can be used to distinguish brachial plexopathy due to radiation as opposed to incidence or recurrence of a mass. Unfortunately, both tumors and radiation plexopathy can exhibit hypointensity on T1-weighted imaging and hyperintensity on T2-weighted imaging as well as enhancement following gadolinium contrast; the most reliable sign is the detection of a visible mass in the case of tumor recurrence. The MRI features of acute and chronic brachial plexus changes following radiation are outlined below ^1,2:

Acute radiation plexopathy

• diffuse, uniform, symmetric swelling, hyperintense on T2-weighted imaging
• slight to moderate hyperintensity on STIR images
• can have mild contrast enhancement
• surrounding fat and muscles appear diffusely T2-hyperintense
• radiogenic pneumonia and pleura thickening possibly present

Chronic radiation fibrosis 

• usually hypo or iso-intense on T1 and T2
• does not enhance with gadolinium 
• architectural distortion and more diffuse thickening of brachial plexus without a focal mass
• surrounding fibrovascular scar tissue

This case has more features of chronic radiation fibrosis.

Case courtesy of Dr Craig Hacking and A/Prof Pramit Phal.