Therefore, careful ophthalmic follow-up with visual acuity testing, pupillary examination, and confrontation visual field testing with quantification (when possible) is important to determine whether there are signs of progression. No specific data are available regarding the use of visual evoked potentials to assess the status of vision with these tumors. Rarely, these tumors become large enough to occlude the third ventricle and cause obstructive hydrocephalus. Children with hydrocephalus may or may not have papilledema. The presence of papilledema is dependent on the degree of optic atrophy present. When optic atrophy is present, the optic nerves may not have enough axons to demonstrate optic disc swelling despite the presence of raised intracranial pressure in association with the hydrocephalus. (Please see discussion below about management of papilledema.) Other ophthalmic findings from hydrocephalus could include Parinaud syndrome and cranial nerve palsies, usually of cranial nerve VI.

Tumors of the optic chiasm are frequently associated with endocrine dysfunction, even when there is no clear involvement of the hypothalamic structures or pituitary [17]. Interestingly, optic chiasm glioma is associated with accelerated systemic growth and secondary sex characteristic development, also known as precocious puberty. Irradiation of the optic chiasm for treatment of progressive tumor induces hypopituitarism. Children treated with radiation therapy should thus be followed by pediatric endocrinologists [17]. This is yet another risk of radiation treatment, but it may be considered an acceptable risk in cases of a treatment-resistant tumor and progressive visual loss. Monitoring requires careful endocrinologic examinations. A major problem in patients with hypothalamic involvement is hypothalamic obesity, a problem that is extremely difficult to manage and is a major health risk.

Similar to the treatment of optic nerve gliomas, the treatment of optic chiasmal gliomas remains controversial, in that we do not know if the natural history of vision loss in children with these tumors is altered by treatment and there have been documented cases where vision improves without intervention.

34.6 Intraparenchymal Astrocytoma

34.6.1 Description and Clinical Issues

Tumors beyond the optic tract and within the brain parenchyma are usually lowgrade tumors, specifically juvenile pilocytic astrocytoma. These tumors are sampled infrequently, primarily when tumors are resected following treatment failure or when tumor mass effect is producing secondary intracranial symptoms such as obstructive hydrocephalus. Symptoms of visual disturbance are variable, depending on the tumor location along the optic pathway from the lateral geniculate/posterior thalamus. Astrocytomas generally do not develop in the most posterior segments of the optic pathway beyond the thalamus to the calcarine cortex; instead, astrocytomas more often develop anteriorly. Posteriorly placed tumors cause visual disturbances

which include field defects and disorders of visual higher cortical function, such as hemineglect syndromes [18]. Functional studies of vision in these locations are best assessed by formal visual field testing. Of note, when a tumor causes obstructive hydrocephalus, as might occur with a tumor of the posterior thalamus and/or midbrain, patients may develop hydrocephalus and papilledema and secondary visual loss from long-standing papilledema.

Cases of papilledema must be followed closely by an experienced ophthalmologist to determine if visual function is threatened, which would require intervention by shunt placement, third ventriculostomy, and/or optic nerve sheath fenestration. Visual function in children with papilledema may be difficult to follow, especially if the child is young, inattentive, and unable to perform automated visual field testing. Therefore, careful and detailed visual acuity examination, pupillary examination, and quantification of confrontation visual fields must be done with a frequency that is determined case by case, on the basis of the child’s response and ability to quantitate the visual function. Other factors influencing management decisions include the amount of edema, presence or absence of impending postpapilledema optic atrophy, and change over time. When visual failure is threatening, a qualified multidisciplinary team of physicians should be involved in determining the correct procedure and medical management, which may be temporizing (e.g., acetazolamide). As visual failure from undertreated papilledema is usually not reversible, it is imperative to intervene early.

Disorders of higher cortical function secondary to tumor development must not be confused with specific higher cortical dysfunction syndromes commonly associated with NF1. These syndromes include visual spatial and visual motor dysfunction, which are present in approximately 40% of NF1 patients [19]. These syndromes are commonly expressed as various forms of dyslexia and/or dysgraphia and are usually first recognized as learning disabilities in children with NF1 [20]. These cognitive syndromes in NF1 have been well studied and appear to result from several forms of disordered brain development in utero [21–24]. These disorders are easily screened for with the judgement of line orientation test, and this technique should be utilized in assessment of all children with NF1 as part of the full neurocognitive assessment and screening for learning disability [25]. Likewise, a full neurocognitive assessment should be performed on all children prior to treatment of tumors within the brain parenchyma.

Although most tumors of the optic pathway are juvenile pilocytic astrocytomas, other tumor types may develop, including lower-grade and higher-grade tumors. Lower-grade tumors are referred to as hamartomas and are essentially regions of tissue dysplasia without neoplastic features. Unfortunately, mutation of the NF1 gene may serve as a tumor growth promoter (failure of tumor suppressor gene function), causing some parenchymal mass lesions to evolve spontaneously or to recur at resection margins. Primary and recurrent tumors may develop as highergrade astrocytomas, including anaplastic astrocytomas, glioblastomas multiforme, and glial sarcomas.

In patients with NF1, intraparenchymal astrocytomas of the brain stem and cerebellum may occur. Although these tumors are not technically in the sensory visual