Named by a Flemish Anatomist

This case was requested by my friend Kate. I hadn't heard of the diagnosis until she mentioned it; about 1000 cases have been reported in the medical literature.
This patient noticed a swelling in the mid-lower abdomen. Although it was painful, he could "push it in" when he's lying on his back. Within the last day, though, it's become much more painful; he's vomited and hasn't had a bowel movement. On exam you note that the mass is covered by an intact external oblique aponeurosis. It is lateral and inferior to its defect in the space posterior to the external oblique muscle.

Challenge: Specifically, what's your diagnosis?

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