Half a brain

Many children who have had hemispherectomies at Johns Hopkins are in high school, and one, a college student, is on the dean’s list. The families of these children can barely believe the transformation, and not so long ago neurologists and neurosurgeons found it hard to believe as well. I asked (neurosurgeon George) Jallo if he remembered his first hemispherectomy. “Yes and no,” he said. “I don’t remember the patient. It was more of a ‘Wow.’ I was a resident in training and I assisted in one of the operations. I didn’t realize you could take out that much brain tissue and have someone be so functional and useful in society. What amazes me is that, if someone all of a sudden strokes out half of the brain, more likely than not they are not going to survive. Yet a lot of these people develop their seizures when they’re very young, or in utero, and when you take out half of their brain in one sitting it’s as if they weren’t touched.”

There are wide variations in recovery, and any brain surgery carries grave risks. Many factors affect how well a patient does—age at the time of a condition’s onset, age at the time of the operation, the nature of the condition itself, and the determination of parents and caregivers to maintain an intense schedule of therapy before and afterward. Possibly the greatest danger is posed by the brain’s veins and arteries, which are so numerous and so wildly, individually arranged that they are impossible to map and very hard to control. Excessive bleeding can send patients into shock and then into comas from which they never return, or it can wipe out most brain function. The other conflicting challenge of the surgery is the necessity of making sure that enough tissue is removed. Freeman once saw a small boy who made good progress for six months following a hemispherectomy, after which he began to deteriorate. His doctors discovered that they had left a small piece of the excised hemisphere in the child’s head. It was, said Freeman, no larger than the top joint of his thumb. But the electricity from that piece of neural tissue was enough to compromise the remaining hemisphere. The boy had another operation, a “redo,” as the doctors at Johns Hopkins informally call it, in which the bad piece of brain was removed. After that, he had no more seizures.