Cancer can seed to the nodes and when in the early stages WILL NOT be picked up on a scan.
best of luck hopefully you wont have to have a second surgery - friends husband was recently diagnosed with the same cancer and they did the surgery told him he was cured. He went away for a month - a node popped up. When they returned the dr. Looked at it and the cancer was back and spreading and now they are chasing it. If three drs. have suggested a dissection... I would be leaning towards listening. But to each his own.
take care.