Amanda's visit with the pediatric neurologist was yesterday. He examined her, her history, and the xrays and did not see anything alarming. But at the same time, he could not explain Amanda's "clinically" large head (she is above the 97th percentile for head size, although she does not look abnormal). So he recommended a CT scan which would be able to rule out hydrocephalus (excessive fluid on the brain).
We haven't decided whether to go with the doctor's recommendation or not. Of course, we want to be vary careful and conservative concerning our daughter's health. But it's just hard to believe something is wrong with her when she has no other symptoms. And the CT scan isn't simple: she'll have to be given general anesthetic for the 2-minute scan, which means she can't eat anything for 6 hours beforehand as well as incurring risks inherent to anesthesia.
Also, her twin sister, who apparently does not have a dangerously large head, has a head circumference 0.25" less than Amanda. That seems like it's such a small difference that either Elena should be checked too or it indicates that large heads are just a Reid trait (according to the data, both girls have heads larger than the average 3-year-old).
Maybe we'll ask our parents if large heads runs in our families, since none of us are hydrocephalitic.
Of course, if we do end up getting the CT scan, I'll try to get a hold of the images, and I'll post them here.