As you can see there is abrupt narrowing and upward curving of the proximal celiac trunk.

Answer: Celiac artery compression syndrome (aka median arcuate ligament syndrome). - essentially a low inserting median arcuate ligament (connects the L and R diaphragmatic crura) which compresses the celiax trunk, especially with gastric distention (post-prandial)

Remember this can be a NORMAL findings especially with expiratory imaging. So you need a good history to correlate with (In this case they actually called looking for it!)

Short Ref: http://radiopaedia.org/articles/coeliac-artery-compression-syndrome

Detailed Ref: http://pubs.rsna.org/doi/full/10.1148/rg.255055001