My son has struggled with constipation since he was 2 weeks old. He is now 28 months and is considered a failure to thrive child. He had an ultrasound when he was about 6 months of age due to a sacral dimple on his back. It said the thecal sac was not well assessed due to shadowing from the patients age. Should they have issued an MRI? Does anyone else have problems like this with their child?