Rapidly Increasing Head Circumference

If your son is developing normally (sounds like he is...many kids do not speak at 13 mo) then I would leave it alone for now. My friend had a baby born w/ hydrocephaly (& many other birth defects) so I have researched it some. Another friend had a baby with large head circumference & they did a test at the dr's orders...I think the ct scan...and determined he had some sort of hydrocephaly...but it was a minor kind & he will be fine & live a normal life. If I were you I would get a 2nd opinion. I wouldn't necessarily jump into a ct scan b/c there is radiation involved, but if you are truly concerned, I wouldn't let 1 dr's opinion suffice. Can you go to a developmental pediatrician or a specialist in the area & get their opinion? Maybe you should wait a few months & see where the #'s fall. My daughter had a bigger head at birth (looking back, it seemed very big!), and a petite body. A larger head doesn't necessarily mean something scary like fluid in the brain. When in doubt, get a 2nd opinion. I wish you the best!

It sounds like developmentally your child is just fine. My sons head was in the 'greater than 98th percentile' range. At the same time his weight was in the 20th. He is perfectly fine. The dr never recommended a ct-scan even though he was basically off the charts. All kids develop in their own way. I know it is hard not to worry but I would just keep an eye on him, get a second opinion to reassure yourself if you need to. Actually since he was failing to thrive I would take it as a good sign. As we say in our house 'Big head, big brain' :o)

my son was diagnosed with failure to thrive at two weeks old. it took a while for him to get up to speed with the other children. i had the same concerns as you, but everything turned out ok. he is now i hyperactive(normal lol) almost three year old :) i was paranoid and had him tested for all kinds of stuff, he didnt have anything, but its always better to be on the safe side.

You say he is "crawling, standing, cruising, pointing, smiling , laughing,
has eye contact, responds to name and seems to be pretty intelligent".
Well, he sounds pretty intelligent to me.
Words come later.
Please try not to worry.

Not sure if I totally understand what you are asking... but both my girls heads are in the 90th+ percentile and the rest of the body is 25-50.
They are totally normal, growing well, eating well, sleeping well.
My 2 year old speaks well, is potty trained and a joy.
My 1 year old is starting to talk, is on track for everything and is a real ham! So I don't think there is anything wrong with having a big head and a smaller body. And to be honest when I tell people they have large heads most folks look at me like I am crazy. I mean it isn't like that have this odd huge head on this tiny body. They look normal.
I only know they do have big old heads because I have the hardest time getting clothes over them lol.
Anyhow if the doc isn't worried I would say stop reading the internet and relax. If your kiddo is doing well, healthy, happy and hitting all milestones, then I am sure all is well.