First, the MRA (MR angiogram) proves marked extrinsic compression of the left subclavian artery (first image below). A second image from the MRA shows an aneurysm of the subclavian artery just distal to the point of maximum compression. Severe narrowing of the artery is known to create turbulent, high-velocity blood flow. Under the right conditions, this causes damage to the arterial wall, resulting in an aneurysm. Left unaddressed (or unknown without this imaging test), blood clots can form in the aneurysm, and cause distal gangrene.
Note the dark background of the MRA. This has been done intentionally, to maximize the signal from the arteries. Unfortunately, we have no way of knowing what structure is causing the arterial compression from these images alone.
Second, the MRI clearly demonstrates small to moderate bilateral cervical ribs. None of the patient’s medical records showed that her doctors were aware of these extra ribs.
Third, the MRI shows focal marked thickening of the left brachial plexus as it crosses the cervical rib.
The MRI images below demonstrate these findings. Note that the bright arteries previously seen on the MRA are now black, and almost impossible to assess.
Fourth, provocative imaging with the patient’s arms over her head proves marked compression and angulation of the brachial plexus at the point of thickening. The MRI images below are performed with the patient’s arms raised. Compared to the images above (with the arms down) these images show how arm motion causes compression of the brachial plexus.