Cerebral palsy is a general term for a group of conditions that involve neurological impairment during early childhood development. It may involve problems with regulation of motor function, defective development of mentation, or impaired acquisition of specialized skills, such as speech. Neurological damage may be due to faulty development of the nervous system or injury during the perinatal period, and it may be diffuse. Although the disease is not progressive, some of the manifestations may not become apparent until the motor system begins to mature or the child fails to meet developmental milestones during the first 3 to 4 years. Some patients may have profound impairment of motor function but normal or even superior mentation, whereas the reverse may be true in others. Many cases of cerebral palsy can be attributed to cerebral anoxia at birth. Clinical manifestations and neuropathologic findings are variable, but motor disorders may generally correlate with lesions or atrophy in the basal ganglia or cerebellum. Several manifestations of cerebral palsy may lend themselves to neurosurgical intervention. Choreiform movements are abrupt, irregular fast movements, usually of the distal extremities. Athetosis consists of slow, writhing movements involving the entire extremity or trunk. These two types of involuntary movements are frequently combined in cerebral palsy as choreoathetosis, and are often accompanied by spasticity, dystonia, and/or ataxia. The long-term nature of the motor disability frequently leads to contractures. Only patients with choreoathetosis and/or spasticity with good mentation and motivation should be considered for surgery. There is not agreement about potential benefit of surgical intervention for choreoathetosis in cerebral palsy, to some extent because of the difficulty in evaluating improvement in these patients. Improvement occurs only gradually. Patients may look the same after treatment but may have improved function. Involuntary movements may still be obvious, but activities of daily living such as self­care, dressing, and feeding may become possible. There is so much variability among patients that it is difficult to draw general conclusions.

It is important to remember that patients with cerebral palsy have not had the opportunity to acquire a repertoire of patterned motor behavior. As the involuntary movements or spasticity wane, it is still necessary for the patient to train the released muscles to do voluntarily that which would have developed automatically habilitation, rather than rehabilitation. Consequently, it can be argued that clinical improvement may be the result of continued physical therapy rather than surgical intervention. Some manifestations of cerebral palsy do not lend themselves to neurosurgical control, such as difficulties with speech or mentation. Severe impairment may be a contraindication to surgery.

Choreoathetosis, but not spasticity, may be improved with ventrolateral thalamotomy or campotomy, with thalamotomy being used more frequently. It is usually necessary to use general anesthesia for cerebral palsy patients, but if the lesion is made in the ventrolateral nucleus, the optimal target point for choreoathetosis may be identified by the appearance of hyperkinetic movements on electrical stimulation, usually in an area that is frequently fairly anterior in the ventrolateral nucleus. If spasticity is the dominant symptom, dentatotomy may be useful, especially lesions in the ventrolateral portion of the dentate nucleus, which are usually made bilaterally during the same procedure. Localization of the target point may be obtained physiologically by eliciting motor responses, chiefly of the ipsilateral axial musculature. As an illustration of the difficulties with evaluating the effects of such procedures, there is disagreement as to whether the primary effect is expressed ipsilaterally or contralaterally, but most patients require bilateral dentate lesions. The effect of stereotactic surgery may decrease over time, but a long-term improvement in spasticity in 30 percent of patients has been seen, with some facilitation of nursing care in 50 percent of patients. One large series reported significant improvement in 78 percent of cerebral palsy patients following thalamotomy, particularly improvement in leg scissoring, and inversion, facial grimacing, and spasm of the shoulder and rectum.  Another report showed that only 18 percent of patients were markedly improved but 32 percent had moderate improvement, with less improvement demonstrated in many patients at long-term follow-up evaluation. Chronic stimulation of the anterior lobe of the cerebellum has been reported to be of benefit in treating spasticity in cerebral palsy patients. Physiologic effects can be demonstrated by the reduction of amplitude of somatosensory evoked potentials in the H reflex with chronic cerebellar stimulation. A four-contact electrode is inserted over the cortex of the anterior lobe of the cerebellum on each side through small craniectomies just below the transverse sinus. The electrodes are activated by a radio receiver implanted in a subclavicular pocket and controlled by an external radio transmitter. Stimulating each lobe alternately at a rate of 200 Hz appears to afford the best result with the least fatigue. One report suggested that significant damage may occur under the electrode, but later reports indicated that these results may have been artifacts associated with the size of the electrode and current densities, and that attention to the regulation of stimulus strength provides a significant safety factor. In addition to the original reports of improvement in spasticity, there has been suggestion of subjective improvement in choreoathetosis with chronic cerebellar stimulation, but this improvement has not been well documented. Chronic cerebellar stimulation might be recommended for those patients with good mentation who may improve activities of daily living with modest improvement in spasticity or choreoathetosis.