Ill-defined increased T2/STIR signal intensity involving the proximal radioulnar intraosseous space and the supinator muscle with volume loss of the supinator muscle – may suggest Posterior Interosseous Nerve Syndrome.
A linearly oriented T2 hyperintense structure positioned between the superficial and deep fibers of supinator muscle – likely suggestive of thickened/edematous posterior interosseous nerve.
Recommend clinical correlation, further evaluation, follow up.