A question...

[FlowRock]

my boa has a single line of scales from his back to his belly, that stands up a little and looks cranked. At first I thought he might have scratched himself or something, but it seems to be a permanent thing, cause he shed three times meanwhile and the line is still there, not expanding, what would have concerned me, but still visible. There is no sign of infection or wound or anything, just these line with three exceptional outstanding or lets say cranked scales.
Any idea what that could be???
He does not seem to be affected in any way, growing, eating, pooping, shedding all fine, temps and humidity are as recommended.

Edit:
I have to say I am not quite sure if this have not been there since I got him, I just realized it since he doubled his size (more or less) till today.