Hemispheric Tumors

Hemispheric Astrocytomas

Astrocytomas are the most common supratentorial tumors in childhood, constituting approximately 30% of such tumors. There is no gender predilection. Most cases in children are benign, but more malignant grades (e.g., glioblastoma multiforme) can occasionally occur. In general, the duration of symptoms before diagnosis is longer with supratentorial than with infratentorial astrocytomas. Supratentorial tumors are often large at the time of presentation.

The clinical signs of cerebral hemispheric astrocytomas are generally determined by the tumor location. Signs and symptoms of increased intracranial pressure, seizures, and focal neurologic deficits predominate. Headaches may be focal or diffuse; persistent focal headaches may have a localizing value. Seizures are relatively common, presenting abnormalities of hemispheric tumors, ranging in incidence from 30 to 60% of cases. It should be emphasized, however, that the incidence of tumors in children with epilepsy is quite low in general. They tend to occur more frequently in the slow-growing astrocytoma than in the rapidly growing glioblastoma multiforme and, in this respect, can be considered a good prognostic sign. Seizures are more likely when tumors involve the sensory-motor strips of the cortex or the temporal lobes. Ataxia may be present with tumors of the frontal lobes or thalamus, presumably due to involvement of the frontopontine pathway, and this may lead to the incorrect diagnostic suspicion of a posterior fossa process.

Neuro-ophthalmologic abnormalities may arise from direct involvement of the geniculostriate pathways or from hydrocephalus. Visual field abnormalities and papilledema are the most common neuro-ophthalmologic signs. Involvement of the frontal gaze center causes an inability to look volitionally to the contralateral side while retaining reflexive eye movements to that side. If the lesion is irritative rather than paralytic (as in tumor-associated seizure activity), there may be tonic conjugate deviation of the eyes toward the side contralateral to the lesion. Tumors involving the deep parieto-occipital regions may be associated with defects in conjugate horizontal pursuit to the side of the lesion in association with contralateral homonymous hemianopia. Therefore, deep parietal tumors often produce loss of horizontal optokinetic responses toward the side of the lesion, while occipital tumors do not (Cogan’s rule).191

Cerebral astrocytomas may appear on CT scanning as solid, with a central necrotic area, or cystic, with an enhancing mural nodule. The tumors are typically found deep within the cerebral hemispheres but can occur in the centrum semiovale or cortex. It is usually impossible to differ-

entiate benign from malignant astrocytomas of the cerebrum with MR imaging, although low-grade tumors tend to be homogeneous, whereas higher-grade tumors show considerable heterogeneity. No definitive MR criteria exist to differentiate cerebral astrocytomas from ependymomas or oligodendrioglioma.

The best prognosis is attained by patients with benign cystic astrocytomas resembling their infratentorial counterparts.590 These can be cured by total excision and may show prolonged symptom-free survival, even after subtotal resection. The therapeutic role of radiation in these tumors is under debate. In contrast, children with glioblastoma multiforme or anaplastic astrocytoma require radiation and, potentially, chemotherapy.264

Gangliogliomas and Ganglioneuromas

These tumors differ from most CNS tumors in that both neuronal and glial elements are involved in the neoplastic process. They are labeled as gangliogliomas when the glial elements predominate and as ganglioneuromas when the neuronal elements predominate. There is no gender predilection.

These tumors are slow growing and frequently present in the second decade of life or beyond with a long history of focal neurological deficits. The specific clinical manifestations depend on the location of the tumor. If the motor cortex or the temporal lobe is affected, patients present with a long history of focal seizures.861 If the occipital lobe is affected, homonymous hemianopia may result. The treatment is surgical resection.

Supratentorial Ependymomas

Supratentorial ependymomas are histologically identical to their infratentorial counterparts and tend to peak in incidence between the ages of 1 and 5 years. There is a slight male preponderance. The presenting clinical features depend upon the location of the tumor, with focal seizures and signs and symptoms of increased intracranial pressure being most common.277,351

Primitive Neuroectodermal Tumors

Primitive neuroectodermal tumors (PNETs) are a group of highly malignant tumors found primarily in the cerebral hemispheres of children and young adults. They represent a pathologic quagmire in that there is considerable confusion regarding their differentiation on pathologic grounds from