Two out of three is not bad. After my cancer came back and I had the surgery, they only get the bare minimum for "clean: margin and the pathology report showed PNI. Most of the medical articles on PNI are for other cancers but here is a google book link on one about Head and neck Cancer.
What is very interesting is that is debunks the old concept that PNI happened through the lymphatic channels. It turns out the tumor Directly invades the perineural space.
While it is indeed good that the lymph nodes taken out were all clean, it also means they did not have to come out. New posters get upset when I point this out. I was lucky my ENT surgeon already knew that the PNI/lymph node connection was bogus so I did not have one the first time around. Since they had to do "big surgery" (from your signature line - the technical name is salvage surgery), it does make sense to do a modified radical neck dissection and Yes, my good lymph nodes were taken out also - but the original two lymph nodes that the cancer had spread to (that's the N2 in my staging) were totally necrotic (dead) from the radiation and chemo so if the cancer had not come back, I'd still have a robust lymph system.
In my case, the doctors decided to give me a whole second round of radiation and chemo because of the PNI. Otherwise my ENT felt that the cancer would come back yet again. I already had the "maximum" so they did CyberKnife instead.
Don't forget this article's statistics should be put into the context that for individual patients like your Dad and I, it's either 100% or zero. PNI is most definitely NOT a death sentence.
PNI: chapter 33 H&N Cancer
Charm