Choose your Seat Wisely

A 54 yo orthopedic surgeon has been training for 10 years to enter the senior circuit of the Tour de France. He cycles rain or shine for the equivalent of 100 miles per day. During a training mission a week before his departure date for France, our orthopod is hit by an automobile and lands on the pavement with a hard splat. He is taken to the emergency room where after describing his pain to the clinician on call, it appears as if he has broken his pelvis. No evidence of a broken pelvis is noted after imaging.  But significant large masses can be seen in the region of the iliac artery. The orthopedic surgeon confesses to the emergency clinician that he has been having difficulty voiding for about a year, and that he attributes his difficulties and sometimes inability to empty his bladder to his training regimen including his reluctance to use a modern “training” bicycle seat. It becomes clear to both physicians that the large masses need to be biopsied.

Question: Metastasis from which labeled structure is most likely to drain to the iliac nodes?

Postscript: Needless to say, the trip to France is postponed. Instead, our orthopod visits his favorite café on the Costa Brava in Spain to mull over his next adventure ....