I would definately seek another opinion about tethered cord or even Chiari Malformation. Most dr's overlook Chiari Malformation as an incidental finding on an MRI of the brain, and don't even mention it to the patient/parent.
If there was a dimple noted on the back, its worth seeking a second opinion.
There is a yahoo group specifically for parents of kids with tethered cord, as well as chiari malformation. I don't have the website offhand, but you can google "yahoo groups tethered cord", and it should come up for you.
Good luck
Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine your son and obtain a full history, I can not unfortunately provide you with a diagnosis for him nor comment on a lot of the information and questions above. However, I will try to provide you with some useful information.
The diagnosis of CP can be made at a later age, it is does not necessarily have to be made in childhood. Cerebral palsy is a disorder that is thought to result from damage to a child's brain in early life. This does not necessarily imply that there was an obvious problem pregnancy and delivery or soon after birth, sometimes no such history is present.Cererbal palsy ranges from mild to severe; sometimes it can be subtle and in such cases diagnosis may be delayed. There are different types based on the signs and symptoms that are present. These may include weakness for example in both legs versus just in the right leg and arm or left, increases in tone, problems with swallowing, and other types in which there are extra abnormal movements (such as a movement called chorea). Some children with CP have motor and cognitive delay (what is often referred to as mental retardation), others have very subtle signs.
The causes of motor delay are extremely variable. Motor delay may result from problems in the brain, such as in CP, the spinal cord, the peripheral nerves, and the muscles. A tethered cord or spina bifida would in all likelihood shown up on MRI.
Clonus is a series of involuntary muscular contractions due to sudden stretching of a muscle. In ankle clonus, extending the ankle upwards suddenly and forcefully would cause stepping-down movements called clonus. A few beats of clonus is not necessarily abnormal. Clonus of 3 beats is not always abnormal; usually 5 beats of clonus or more is abnormal.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.