Infantile Spasms

Infantile spasms are almost entirely seen in the first year of life and are associated with developmental delay, regression, and medically refractory seizures. They present with a typical electroencephalographic (EEG) pattern: hypsarrhythmia. Seizures in infantile spasms are seen in clusters, occur even during sleep, and cause exhaustion and lethargy. Various types of myoclonic seizures, such as flexor and extensor spasms with a cry, are seen and are followed by a brief episode of akinesia. The seizures generally disappear within 5 years-50% before 3 years of age, 90% before 5 years of age. Many conditions can cause infantile spasms, such as neurocutaneous syndromes, congenital brain malformations, metabolic and degenerative diseases, and hypoxicischemic insults.12

Hemiconvulsion-Hemiplegia-Epilepsy Syndrome

HHE syndrome is most frequently seen within the first 2 years of life. The initial phase of the syndrome presents with unilateral, prolonged hemiconvulsive seizures that involve the face, arms, and legs. The second phase is characterized by hemiplegia, and the third phase is characterized by partial epileptic seizures. The syndrome progresses to chronic epilepsy within 1 to 2 years. Although there are many possible causes for HHE syndrome, including meningitis, subdural effusions, trauma, and hemispheric lesions, in many cases, no cause can be determined. The etiology of this condition is still poorly understood. In the course of the disease, hemiatrophia cerebri develops gradually after hemiconvulsive seizures and hemiplegia.12,13

Sturge-Weber Syndrome

Sturge-Weber syndrome is a progressive neurocutaneous disorder associated with pial angiomatosis involving the cerebral cortex, along with a cutaneous angioma in the trigeminal nerve territory on the face and scalp. Facial angioma (port wine stain) is seen in 90% of cases. Facial and lepto-meningeal angiomas occur mostly uni- and ipsilaterally but can also be seen bilaterally in up to 20% of patients. Pial angiomatosis mostly involves the parietooccipital region, but it can be extensive and may involve the entire hemisphere in some cases.

Sturge-Weber patients have a very peculiar leptomeningeal vascular bed, with hypertrophic pial vessels and frequently absent major venous sinuses and cortical bridging veins. This peculiar vascular anatomy creates a strong retrograde venous flow into the ventricle. This abnormal he-modynamic induces hypoxia in the surrounding brain tissue because of the diversion of cerebral blood flow away from the parenchyma and associated venous stasis. This abnormal blood circulation eventually causes cellular damage in the brain parenchyma and secondary seizures.

The most common symptoms in Sturge-Weber patients are seizure (75–90%), developmental delay, hemiparesis, and various ophthalmologic problems, such as glaucoma and optic atrophy. Seizures are usually the earliest symptoms in Sturge-Weber patients, with 70% of patients experiencing seizures in the first year of life. Seizures may even occur during the newborn period. If the seizures start in infancy, the prognosis is guarded. Most seizures are simple/ complex partial seizures, with frequent secondary generalization, and are often unresponsive to medications (only 10% respond well to medications). Patients may develop hemiplegia after an episode of serial seizures in the first year of life. Therefore, vigorous treatment is essential to prevent postconvulsive damage during infancy. Although hemispherectomy is the main treatment modality in Sturge-Weber patients with severe epilepsy and should be considered after diagnosis, but waiting until a child is 1 year old before proceeding to surgery may be also a reasonable approach in some cases to prove the intractability of the seizures.12–15

Hemimegalencephaly

Hemimegalencephaly is an extensive neuronal migrational disorder involving the entire hemisphere. This abnormal, unilaterally enlarged hemisphere generally has no cortical lamination; a wide, thickened, and flattened cortex; and shallow gyri. Other abnormal histological and radiological findings include reduced number of sulci, reduced white matter volume, subcortical heterotopia, calcifications, poor gray-white matter differentiation, hypoplastic corpus callosum, and an ipsilaterally enlarged or shrunken ventricle. The frontal and occipital lobes in an abnormal hemisphere are frequently hyperplastic, unlike the hypoplastic temporal lobe.

Hemimegalencephaly can be seen as an isolated entity or may be associated with Klippel-Trenaunay syndrome, hy-pomelanosis of Ito, linear nervous sebaceous of Jadassohn, or Proteus syndrome. Medically intractable seizures are the most common finding and generally start during infancy. Severe epileptic encephalopathy and developmental delay are common in these patients. If the seizures are not well controlled, patients may develop hemiparesis, hemianopia, and mental retardation. High mortality rates in the first months of life are seen in these patients because of the continuous seizures.12,13,16

Cortical Dysplasia

Unilateral multilobar or extensive cortical dysplasia is another congenital condition associated with medically refractory epilepsy in early childhood. Hemispherectomy or multilobar resections are frequently the best treatment options for these patients. Further information about this condition can be found in Chapter 22.

Rasmussen Syndrome

Rasmussen syndrome is a chronic encephalitis that is characterized by intractable epilepsy and progressive atrophy in one hemisphere. The syndrome was first described by Rasmussen in 1958. Although seizures in Rasmussen syndrome frequently start with a generalized tonic-clonic seizure, they usually continue as partial epilepsy.

Rasmussen syndrome is a progressive disease that causes hemiplegia in the majority of cases. The results of initial imaging studies are normal, but follow-up imaging studies reveal unilateral ventricular enlargement, followed by hyperintense changes and, finally, focal atrophy in the primary sensorimotor cortex and insula. Mesial temporal involvement in these cases is frequently seen very late, and occipital involvement is seen even later.13,17,18 Further information about Rasmussen syndrome can be found in Chapter 26.

Porencephalic Cyst

Perinatal vascular insults, such as internal cerebral artery and middle cerebral artery infarcts, intracerebral hemorrhage secondary to arteriovenous malformations and congenital coagulopathies, and traumatic brain injuries can cause large, hemispheric porencephalic cysts.14,17 These patients frequently have unilaterally enlarged ventricles and severe brain atrophy secondary to extensive tissue loss, with large porencephalic cystic areas. Medically intractable seizures and hemiplegia are frequent findings in these patients, who are ideal candidates for hemispherectomy and, especially, hemispherotomy procedures.

Medical Intractability

As in all epilepsy surgery cases, the first step in preoperative assessment is determining the intractability of the seizures. Although some patients may require extensive trials to prove that the seizures are intractable, children who have seizures secondary to hemispheric lesions rarely need exhaustive trials to prove medical intractability. Determining the intractability of seizures to major antiepileptic drugs (AEDs) may be relatively easy in patients with hemispheric lesions, such as Rasmussen syndrome, Sturge-Weber syndrome, and cortical dysplasia because of the very nature of these conditions. Conversely, patients with other conditions may require more time and effort to document the intractability of their seizures.

Clinical Status

The ideal candidate for hemispherectomy is a medically intractable epilepsy patient with hemiplegia and hemianopsia secondary to unilateral hemispheric damage. However, if the patient has no motor weakness or has only mild hemiparesis and partial hemianopsia, surgery will provide good seizure control, with the price being impairment of the patient’s neurological status. The decision for surgery in these patients is not straightforward, and opinions about the suitability of these patients are frequently controversial. Nevertheless, some of these patients may be selected as surgical candidates for hemispherectomy because of the severity of their seizures and the debilitating effect of these seizures on the functional status of these patients.

Certain progressive conditions, such as Rasmussen syndrome, have a well-known natural course that eventually results in motor and cognitive worsening. Patients with catastrophic infantile epilepsy syndromes may present with hundreds of daily seizures, resulting in no functional life; these seizures pose a very high risk of damage to the developing brain. Even if these patients do not have hemi-plegia, they may still be considered candidates for hemispherectomy procedure because early surgery may prevent an eventual decline in cognitive function and psychomotor development.5,15–19

Electroencephalographic Assessment

Preoperative ictal and interictal EEG studies help to verify the unilaterality and determine the extent of the epileptogenic zone. Determining the extent of the epileptogenic zone is especially important for deciding whether a hemispherectomy is needed or whether a limited cortical resection will suffice. Most important, it should be preoperatively proven that a patient’s seizures are unilateral and the epileptogenic zone is contained within the damaged hemisphere.

Predictors of a good outcome in these patients are the presence of ipsilateral suppression of electrical activity associated with multifocal epileptogenic abnormalities confined to the damaged hemisphere, bilateral synchronous discharges spreading from the abnormal hemisphere without contralateral slowing, and the absence of generalized discharges, bilateral independent spiking, and abnormal background activity in the “good” hemisphere. Sporadic epileptiform activities, some abnormal secondary or independent EEG findings, and nonepileptiform abnormalities in the “good” hemisphere that are seen in some patients do not exclude those patients as candidates for hemispherectomy but may imply an unfavorable outcome, especially if independent interictal sharp wave activity in the “good” hemisphere is present.13,14,17,20