In spiral galaxies, the "arms" follow the golden spiral.
The golden spiral, is a spiral thats shape follows the fibonacci sequence, so it grows out in the spirals on the inside starting at one unit, then one again, then two, then three and five, etc..
This golden spiral can be found in the shape of the "arms" of galaxies if you look closely and do the math.
The spiral may not be perfect, but it is clearly evident.
It can not be told if it is a perfect spiral, because we can not measure a galaxy,but on paper we can measure it and see the size of that, possibly finding an answer.