Knot on Barred Rock head

[Robeenop]

I have a barred rock 6 yrs old with a pea sized knot above her eye. It feels solid. It doesn't bother her in any way. She is the alpha in on of my coups. I call her knot head. Has-been this way for 3 months or so. Thinking maybe a bite that healed this way or timer.
Is perfectly round black pea. Any ideas?

 

[Anime2lover]

Pics would help.

 

[Robeenop]

I stated BR she is actually a Black Astrolorp. Possible tumor or scar tissue?

 

[Anime2lover]

I stated BR she is actually a Black Astrolorp. Possible tumor or scar tissue?

Could be caused by either of those. Chickens can also get cancer just like people. Would you post some pics of your hen?