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• Most brainstem neoplasms are high-grade astrocytomas; the remainder are low-

grade astrocytomas and ependymomas. The exact distribution of these tumors is difficult to assess given the low rates of biopsy confirmation in most series because of significant morbidity and mortality.

• Use of CT and MRI has increased the accuracy of diagnosis of brainstem lesions.

• Intrinsic diffuse brainstem lesions that originate in the pons and have rapid onset of symptoms at a younger age are usually high-grade glioma on biopsy. Lesions in the midbrain or thalamus, those with discrete focal lesions, or those with dorsally exophytic tumors often occur at an older age and have a more indolent clinical course; biopsy, when available, usually confirms a low-grade malignancy.

• Intense homogenous enhancement, particularly within a focal lesion, may suggest a

juvenile pilocytic astrocytoma rather than a high-grade glioma.

• Other processes confused with primary brainstem tumors include abscess,

neurofibromatosis, demyelinating plaque brainstem arteriovenous malformation, and encephalitis.

Treatment

• Corticosteroids usually are necessary to stabilize neurologic symptoms; patients with

severe hydrocephalus may require emergency shunting.

• Surgery has a limited role in brainstem glioma; patients with diffuse pontine lesions

(most patients) do not benefit from surgical resection. Dorsally exophytic tumors, cervicomedullary tumors, and focal brainstem tumors may be amenable to resection.

• Radiation therapy is the mainstay of treatment. For diffuse lesions, inclusion of the entire brainstem, from the diencephalon to the C-2 vertebral level, is recommended; cerebellar extension must also be covered with a 2- to 3-cm margin. More focal lesions may be treated with smaller fields with 2-cm margins. Design of the lateral portals is greatly facilitated by correlation with sagittal MR contrast-enhanced T1- weighted images. Irradiation doses of 50 to 60 Gy in 1.8- to 2.0-Gy fractions are recommended. Because most brainstem tumors fail in the irradiated volume, attempts have been made to escalate the dose to improve local control.

• Hyperfractionation has been investigated extensively in phase I and II trials: Total

doses up to 78 Gy in 78 fractions at 1 Gy twice a day have been delivered. Preliminary results showed no benefit to hyperfractionation over conventional fractionation.

• In a phase III trial, the Children's Cancer Study Group (CCSG) found no benefit to

adjuvant chemotherapy versus irradiation alone. Aggressive high-dose chemotherapy with bone marrow rescue was not of benefit in phase I and II trials. Neoadjuvant chemotherapy has produced clinical and radiographic response, but without clear improvement in survival.

• Ependymal tumors may arise anywhere within the brain or spinal cord, in close proximity to or distant from the ventricular system.

• Myxopapillary and subependymoma variants may behave more indolently than

ependymomas in general.

• A malignant variant of ependymoma termed malignant ependymoma or anaplastic

ependymoma is recognized.

• Ependymoblastoma, a poorly differentiated embryonal variant with a marked

propensity for CSF dissemination, is believed to be a variant of the primitive neuroectodermal tumor (PNET).

• Histologic classification is controversial. Because these tumors are uncommon,

investigators generally combine grade I and II tumors as "low grade" and grade III and IV tumors as "high grade." In 1983, WHO published a simplified grading system.

Treatment

• Emergency management may require corticosteroids or CSF diversion for a

symptomatic mass or hydrocephalus.

• Because modern series confirm a survival benefit and a lower risk of CSF

dissemination in patients with total excision of the tumor, it should be attempted in all patients before adjuvant therapy.

• Surgery alone may be sufficient in selected patients with low-grade, noninvasive

tumors with complete resections, although a substantial risk of recurrence, even in gross totally resected tumors, may argue for adjuvant therapy in all patients.

• Patients with low-grade tumors should be treated with partial-brain irradiation only, because substantial evidence exists that these tumors are more likely to fail at the primary site than in other areas of the brain (31,39).

• Many patients have infiltrative tumors amenable only to subtotal resection, and in

these cases postoperative irradiation should be considered.

• If possible, wedged-beam pair field arrangements should be used to spare as much

cerebral cortex as possible from full-dose irradiation. Whether the entire ventricular system should be included in the treatment field is not certain, although it seems reasonable to do so when it is invaded by tumor.

• High-grade supratentorial tumors should be treated with cranial irradiation only,

because the incidence of spinal seeding is low.

• For posterior fossa tumors, special attention should be directed to the upper cervical

spinal cord, because 10% to 30% extend down through the foramen magnum to the upper cervical spine (31,39).

• All patients with posterior fossa tumors should have CSF spinal axis staging,

including CSF cytology, although the significance of a positive result is uncertain. The incidence of high-grade and infratentorial tumors relapsing within the CSF led to the recommendation to treat with craniospinal irradiation. More recent series document a low overall incidence of isolated spinal relapses, even among the highest-risk

patients; most spinal failures are associated with local recurrences. Because of the morbidity of craniospinal irradiation, especially in young patients, more selective use of this modality is appropriate. Pathologic review is essential to rule out

ependymoblastoma and medulloblastoma, as these tumors have a much higher risk of neuraxial spread.

• Patients with neuraxial spread (positive myelogram/MRI or positive CSF cytology) or

high risk of CSF dissemination (ependymoblastoma, large intraventricular component of tumor) should receive craniospinal irradiation (36 to 40 Gy in 1.6- to 1.8-Gy

fractions), with local boost to the areas of gross disease and primary tumor (total dose of 50 to 54 Gy).

• Patients in whom craniospinal irradiation is not indicated should be treated with

generous local cranial fields, encompassing the preoperative tumor volume with a 2- cm margin, to doses of 54 to 55 Gy in 1.8- to 2.0-Gy fractions.

• Anaplastic ependymoma is treated in a manner similar to low-grade ependymoma.

Total dose to the primary tumor is somewhat higher (55 to 60 Gy). Some authors also recommend craniospinal irradiation in these high-grade posterior fossa tumors, given the perceived increased risk of spinal seeding.

• Chemotherapy is not routinely recommended for patients with ependymoma; previous

trials of adjuvant chemotherapy did not demonstrate a survival benefit. Recurrent