Brachycephaly - how is that different from plagiocephaly?

[Guest guest]

My daughter just graduated after wearing a helmet for 6 months to

correct her plagiocephaly. Now, my 10 week old nephew was diagnosed

with brachycephaly. How is that different from plagio in respect to

repositioning, treatment, facial asymmetries, etc? What does my sister

need to do to try to correct this so that he doesn't have to wear a

helmet also? And what are the causes for brachy? My daughter has tort,

which caused her flat spot, but what could be causing brachy?

Thank you very much for all answers and advice!