My daughter, Daphne, had severe physical and intellectual problems way before her moyamoya was discovered -- even before she suffered two strokes. She began having seizures (20 or more a day) when she was three months old, and lost developmental skills, and withdrew from the world. She had just started to make some progress when she was about 8 months old. She started to roll over, we got control of her seizures with medicine, and she started to become more interactive -- her personality really began to show through. When she was 14 months old, she suffered two, major strokes, and lost everything. She could not move her arms or legs, had difficulty even breathing. She was finally diagnosed with moyamoya, but her doctors told us that it was too late.... she was too far gone for surgery, and they provided us with hospice nursing so that we could take her home.
We did not give up on her, though, and we got in touch with a neurosurgeon (Dr. Steinberg) who thought Daphne could benefit from surgery.
Even before the surgery, Daphne was becoming better. She was able to move her legs, and her left arm, but she was very demanding and seemed to often be in pain.
I can't tell you what a difference the surgery has made in her life. Daphne still has significant challenges... at almost three, she does not walk, crawl, speak or even sit up properly. However, she was 15 months old when she went through her surgery, and she will be 3 years old in less than a month. She is also extremely personable. To know Daphne is to love her; and she is VERY smart. Her vision has improved, her energy has improved, and - overall - she is a much happier, healthier child. She has had no other stroke-like incidences, and her cerebral blood flow has improved by 200%!!!
You mentioned you were already committed to surgery, so I won't lecture you on it's benefits

I know it is a worry going into this --- you have no idea what the outcome might be. But, I know that without treatment, there is a very big risk for losing skills and the personality features that we love about our kids. With surgery, we have a chance to save them, and even improve them.
Jenny (mom to Daphne. www.daphnestory.com)