Most children who present with a single mass lesion in the brain will require a diagnostic procedure, either a biopsy or surgical excision. In general, since metatstatic disease to the brain is exceedingly rare, it is not productive to obtain screening imaging of the chest and abdomen. Preoperative preparation is usually restricted to steroids and anticonvulsants. If a child presents with mass effect from a large lesion, surgery must be expedited, but usually the procedure can be performed electively. If the lesion is located superficially, or in a noneloquent area, most surgeons will plan to excise the mass entirely. If the lesion is located within eloquent areas (e.g., basal ganglia, motor cortex orspeech cortex), a needle biopsy assisted by MRI-guided frameless stereotaxy can be done safely. In some cases, the results of the needle biopsy will prompt a more aggressive second procedure.

In general, obtaining a gross total resection or near gross total resection provides a major prognostic advantage. Specific techniques that improve the ability of the surgeon to remove tumors located within or near eloquent cortex include awake craniotomy with brain mapping, functional imaging such as functional MRI, and magnetic source imaging. Awake craniotomy remains the gold standard for mapping functional cortex, but due to the degree of patient cooperation required, most children under the age of 14 years cannot cooperate adequately. For younger children, if functional information is required, subdural grids can be implanted and bedside testing can be performed when the child is completely awake.

Adjunctive therapy for low-grade astrocytomas remains controversial. For hemispheric pilocytic astrocytomas, similar to the situation with cerebellar pilocytic as-trocytomas, gross total resection is usually curative. For incompletely resected pilocytic

astrocytomas, expectant observation with serial imaging is indicated. Grade II astro-cytomas represent an area of ongoing treatment controversy. If such tumors can be resected completely, patients should be followed expectantly with serial imaging. Some investigators, however, recommend adjuvant therapy in this situation, usually external beam radiation therapy. The improvement in progression-free survival (following radiation) must be balanced against the long-term cognitive sequelae and risk of secondary malignancy. The 5-year progression-free survival for completely resected grade II astrocytomas is approximately 75% to 90%. For incompletely resected grade II tumors, there is disagreement whether these patients should receive external-beam radiation postoperatively, or at time of progression. In addition, most current investigational trials are exploring the efficacy of chemotherapy both as definitive therapy and as a means to defer radiation.

The conventional treatment of high-grade astrocytomas remains maximal surgical resection followed by external-beam radiation (-5500-6000 cGy) to the local area. Median survival for these children remains poor, in the range of 1.5 to 3 years. Aggressive chemotherapy regimens have provided some hope, but long-term survival remains very low.

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