A 29-year-old male presented immediately following a cyclist versus car accident with right wrist pain and swelling. The swelling was prominent, and located primarily over the dorsal aspect of the wrist and hand. A CT image from a study at the time of presentation is shown in Fig. 1, and a sagittal T1-weighted MRI 4 days after injury in Fig. 2. What is the cause of the swelling at the dorsal aspect of the wrist and hand?

Fig. 1
figure 1

CT image from a study at the time of presentation 

Fig. 2
figure 2

Sagittal T1-weighted MRI 4 days after injury