Peds CNS: Optic Tract Tumors

Background

Optic pathway tumors are frequently low grade gliomas. They represent about 5% of childhood brain tumors and involve one of several of the optic system components:

• Optic nerves
• chiasm
• optic radiation

Optic Tract Gliomas are much more commonly found in children less than 10 years old. 75% of all optic tract gliomas occur in these children. They are relatively uncommon in adults. There is a bimodal distribution of ages of incidence with the main peak at 5 years old and a second lesser peak at 52 years. Optic tract gliomas are divided into three anatomic locations: pre-chiasmatic tumors are much more common in younger children while chiasmatic and hypothalamic tumors are much more common in adults.

In children, they are more frequently found in girls. In adults, males are more commonly affected.

There is a strong genetic association with NF1 neurofibromatosis. 10% - 38% of optic tract gliomas have NF-1 and 15% - 40% of NF-1 patients have optic tract tumors. (Note that NF-2 is associated with acoustic neuromas).

As with other brain primary low grade tumors they manifest in a variety of ways. They can be focal or diffusely infiltrating. Tumors of the chiasm are often difficult to distinguish from tumors originating in the hypothalamus. For this reason, these tumors are often grouped together with hypothalamic tumors.

The most common presenting signs are painless proptosis. Other signs include decreased visual acuity, temporal field cuts, appetite or sleep pattern changes (hypothalamus) and new onset headache ± nausea and vomiting associated with obstructive hydrocephalus.

Almost all Optic Path Tumors are low grade gliomas, at more than 90%. These are most often juvenile pilocytic astrocytomas (65%) and Grade II astrocytomas (25%). Gangliogliomas, malignant gliomas, and hamartomas are infrequent

Treatment

Treatment for low grade optic pathway gliomas follows a typical pattern for childhood tumors. For children < 5, avoid radiation therapy using chemotherapy (CDDP/carboplatin/vincristine) to delay radiation. Packer data indicates that chemotherapy can delay onset of symptoms an averge of 3 years. If symptoms develop or progress in the under 5 age group despite chemotherapy, then proceed to radiatin therapy. Radiation doses in the group are 45 Gy.

In older children, ages 5 - 10 years, chemotherapy or radiation therapy are used: CTV = GTV + 5 mm, treating to 50.4 Gy - 54 Gy avoiding hot spots. There are no treatment guidelines for high grade gliomas.

Chemotherapy includes carboplatin or cisplatin + etoposide or vincristine. Lathier prospectively evaluated prolonged chemotherapy consisting of alternating procarbazine/carboplatin, etoposide/cisplatin, and vincristine/cyclophosphamide. The objective response rate was 42% the OS-5 was 89% and 5 year freedom from radiation therapy was 61%. (2003). CCG 9952 is presently comparing chemotherapy regimens: carboplatin/vincristine against thioguanine/procarbazine/lomustine/vincristine.

Radiotherapy

Radiotherapy is typically used when all chemotherapy options are exhausted, when there is progression of disease with symptoms of progression or when there is intracranial extension.

Prognosis

The estimated OS-5 is 89%.

Toxicity

Visual morbidity is the main surgical risk. Common late complications of radiation include endocrine dysfunction and vision loss. There is a high incidence of 2nd CNS tumors (relative risk of 5.3).

The TD 5/5 for hypopitutarism is 40- 45 Gy. Growth hormone levels decrease first followed by LH/FSH then TSH/ACTH.

Radiation Oncology Synopsis