Enlarged c1 transverse process?

[bluebear]

My first question is what is the presenting problem. Is it a limitation of ROM or is she presenting with pain or headaches?

There are a number of good suggestions above as to what an "enlarged" C1 might be, but in my experience, more often than not, an "enlarged" lateral arch of C1 is more commonly a slightly rotated, and hence, more "prominent" with associated spasm/thickening of tissues over the top giving an enlarged feel. In the absence of red flags of course, heat would be a sensible start, and maybe palpate C2 centrally. If the sp process of C2 is deviated towards the same side then it is more likely the inf oblique has spasmed, pulling the two closer to one another. Just be wary with your C2 palapation as its sp process is bifid and not always uniformly. Another good way to check this is to apply a tranverse pressure to C2 from the left and from the right. Is the resistance equal? Is the tenderness equal? If not, again you may have some muscle spasm of the oblique.

If, as you say, she isn't bothered by it at all, I'd be looking to re assure the parents that nothing is wrong, we aren't all symmetrical and probably let sleeping dogs lie.

Cheers,
BB