Visual Pathway and Hypothalamic Glioma, Childhood

Pathology

These tumors can be classified according to the type of nerve cells they most resemble: ependymomas, astrocytomas, oligodendrogliomas, or mixed type. More importantly these tumors can be classified as either low-grade or high-grade tumors. The low-grade gliomas that affect the optic chiasm, anterior [Page 997]ventricle, and hypothalamus are frequently characterized as juvenile pilocytic astrocytomas. These tumors have few mitoses, and no malignant features. However these tumors can progress and cause significant morbidity in young children. Other than age, anatomic location also determines prognosis of these tumors. Optic nerve gliomas can be grouped into anterior optic nerve gliomas and posterior optic nerve gliomas, which affect the optic chiasm. Anterior tumors are more common in childhood, generally benign, and progress slowly. Posterior tumors occur in the very young and older adolescents, form larger masses, and become more symptomatic. Tumors arising in the hypothalamus or anterior third ventricle are less common and more often associated with Neurofibromatosis.

Clinical Presentation

Signs and symptoms of children with visual pathway gliomas consist of proptosis, increased intracranial pressure, and progressive visual loss. Depending on the extent and location of the tumor this can present as either unilateral or bilateral visual disturbances. Asymptomatic bitemporal hemianopsia is the most common finding in chiasmal gliomas. Behavioral changes such as irritability, social withdrawal, somnolence, and aggression may also be seen. This is most likely due to hypothalamic involvement. Endocrine disturbances may also be seen when the tumor involves the suprasellar-hypothalamic region. Characteristics associated with worse prognosis includes early onset in infancy, hypothalamic symptoms and signs of hydrocephalus, presence of diencephalic syndrome, involvement of the third ventricle, and large chiasmal tumors.

Diagnosis

Evaluation of patients with visual pathway gliomas consists of careful family history, accurate assessment of visual status, assessment of endocrine status, and any evidence of increased intracranial pressure. Careful attention should be paid to growth and development parameters as well of the presence of any lesions suggestive of neurofibromatosis or tuberous sclerosis. Diagnostic evaluation should consist of appropriate laboratory testing including pituitary hormones, thyroid function. Formal visual examination, and magnetic resonance imaging (MRI) with gadolinium enhancement for accurate delineation of involved lesions is needed.

Management

Indications for surgery vary based on the type and location of the tumor affecting the optic pathway. When a suprasellar mass is present surgical resection or biopsy is recommended. Definitive management varies based on the origin of the tumor, therefore tissue diagnosis is important. Careful tumor debulking may also improve symptoms. Surgery is usually indicated when there is loss of vision in an eye without extension of tumor to the chiasm. Patients with optic nerve gliomas with minimal proptosis and preserved vision can be followed closely with periodic visual assessment and imaging studies. Radiation therapy is the choice for symptomatic chiasmatic/hypothalamic gliomas in all but very young children. Many recent studies show 90 percent survival at 10 years. Radiation therapy has shown good outcomes in terms of improved vision in 30 percent of symptomatic patients with chiasmal lesions. Permanent radiation induced injury can occur in those receiving external beam radiation therapy. Pituitary and hypothalamic dysfunction as well as memory and intellectual deficits may occur. Young children are known to be at much greater risk than adults. The use of chemotherapy for hypothalamic/chiasmal gliomas has shown promising results and is becoming a popular choice of therapy given the risk of surgical intervention and the consequences of radiation therapy in young children. A combination of actinomycin D and vinblastine has been used with successful results in patients with progressive chiasm and hypothalamic disease.

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