Optic nerve gliomas are
rare, comprising 1% of all intracranial tumors; but 4-6% of all brain
tumors in children. Eighty-five percent occur in children under 15 years
of age and the female/male ratio is 3:2.
About 10 per cent of
optic pathway tumors are located within an optic nerve. One third of the
tumors involve both optic nerve and chiasm, a further third involve
predominantly the chiasm itself, and one fourth are predominantly in the
hypothalamus.5 5% are multicentric.
Although it has
previously been suggested that these lesions are hamartomas, most
authorities now accept that they are truly neoplastic. These tumors are
usually slow-growing low grade (pilocytic) gliomas. Occasionally malignant
ones also found at this location usually in adults. Rarely, a malignant
optic glioma can occur in a child. In childhood, the optic pathway tumors
are low-grade astrocytomas and rarely gangliogliomas. However, optic
pathway gliomas can occur in adults, and in that situation the tumors may
have the characteristics of a highly malignant tumor that causes early
loss of vision and inevitably leads to the patient's death.
tumors may be solid, gelatinous or cystic. Although having certain gross
similarities with oligodendrocytes, closer microscopic, ultrastructural
and immunostaining techniques have confirmed their low grade astrocytic (pilocytic)
nature with the presence of numerous Rosenthal’s fibres. The tumor may
start in the anterior end of the optic nerve and proceed backwards
intracranially or may arise originally from the optic nerve-chiasma
junction. Occasionally, a glioma from the optic tract or the anterior
third ventricle region may involve the chiasma and the optic nerve
secondarily. About 40 per cent of optic pathway astrocytomas are
fibrillary and 60 per cent are pilocytic. Hypothalamic tumors
which have invaded the optic chiasm behave differently, showing evidence
of local invasion and histologically are not pilocytic in nature but are
similar to other cerebral hemisphere gliomas.
About one third of the
patients with optic pathway hypothalamic gliomas will have
neurofibromatosis type1. Patients with neurofibromatosis have
histologically similar tumors but the tumors are more likely to be
associated with extensive arachnoidal hyperplasia and florid local
gliomatous infiltration of the leptomeninges. Indeed, in NF-1 patients
optic nerve lesions may be due to diffuse hyperplasitc gliosis rather than
actual neoplasia. Multicentric tumors involving both optic nerves are also
usually associated with NF-1.
The evolution of
symptoms is slow and insidious and depends on the site of origin. In
general, optic nerve tumors present at a slightly later age (6 years) than
the hypothalamic/chiasmatic tumors (2 to 4 years).
Tumors restricted to
optic nerve produce failing vision in one eye. It is often not detected by
children for a long time. Papilledema (probably due to venous
obstruction), being more common than optic atrophy is the cause for visual
failure. Proptosis is delayed. Optic atrophy in a child with no retinal or
macular degeneration points to an optic nerve glioma, especially in
neurofibromatosis. 20-30% of the patients have café-au-lait spots.
Irregular visual field defect is diagnostic. Initially there is central or
Tumors that involve the
chiasma produce bilateral irregular visual field defect. The loss of
visual acuity is secondary to optic atrophy.
posteriorly located tumors are the most common form of optic nerve gliomas
(60%) and it is often difficult to determine the actual origin of the
tumor as they are frequently large and involve both the chiasm and the
hypothalamus. Patients may present with hydrocephalus (due to obstruction
of the foramen of Monro), visual problems (acuity and field defects),
pituitary dysfunction or hypothalamic dysfunction. The latter, classically
leading to the diencephalic syndrome (emaciation, pallor, and
hyperactivity), is seen in up to 20% of patients under 3 years of age.
When the hypothalamus is involved, particularly in infancy, the child may
present with a diencephalic syndrome.3 Other symptoms of
hypothalamic involvement include diabetes insipidus, anorexia, obesity and
Optic nerve glioma
Lymphoma, Rhabdomyosarcoma, Metastases (Neuroblastoma,
Ewing’s sarcoma), Fibrous dysplasia, Paranasal mucocoele, Meningioma,
neurofibroma, Congenital defect in sphenoid bone)
Optic nerve and chiasm
Optic chiasm glioma
extending into the hypothalamus
adenoma, Craniopharyngioma, Malignant astrocytoma, Epidermoid
dermoids, Chordoma, Colloid cyst, Fibrous dyplasia, Sarcoidosis,
X-ray changes (widening of the optic foramen, shaped sella) have been
superseded by CT and MRI. Bone window setting on CT often reveals
widening of the optic canal. The optic nerve tumor is usually
lobulated but may be smooth and fusiform. It almost always enhances
after contrast. Intracranial tumors appear as low-density lobulated
masses on CT and show inhomogeneous contract enhancement.
MRI is far more
sensitive for displaying chiasmatic/hypothalamic tumors than CT. These
tumors are usually hypointense on T1-weighted images and hyperintense on
T2 and almost always, enhance with gadolinium. On T2, high intensity
signal may be seen extending to the lateral geniculate bodies.
When the tumor involves
the chiasm and the hypothalamus, it can reach an enormous size,
particularly in infancy. In such situations there is often extensive
distention of the basal cisterns, which can rupture, giving rise to large
subdural hygromas that can envelop both cerebral hemispheres.
Visual evoked responses
may be of assistance in monitoring visual function; but it is of limited
They are usually slow
growing and very occasionally may become malignant and grow rapidly. Ten
year survival rates also depend on site and range from 76% to 95% for
posteriorly and anteriorly situated pilocytic tumors respectively. The
treatment remains controversial and is dependent upon the site of the
tumor especially when the optic chiasm and/or the hypothalamus is
involved, and ranges from observation alone to operative intervention with
or without adjuvant therapy. Some physicians advocate resection without
any further therapy, others recommend radiation therapy or chemotherapy,
and still others believe that no therapy is required.
The natural history of
this tumor is variable and spontaneous regression can occur. This should
be kept in mind in deciding on treatment. Patients with an optic glioma
and neurofibromatosis type 1 have a better prognosis than those who do not
Intracranial optic nerve tumors: Not infrequently, asymptomatic optic
nerve tumors are detected whilst imaging patients with neurofibromatosis.
In those patients with reasonable and/or static visual acuity,
surveillance with regular ophthalmological assessment and imaging may be
The aim of surgical
treatment is to remove the tumor before there has been spread to the optic
chiasm or contralateral optic nerve and to deal with the associated
proptosis. Although in patients with orbital optic nerve tumors this may
be achieved with relatively little morbidity via an extracranial resection
(transorbital approach), the risk of leaving tumor in the optic nerve
stump has resulted in most surgeons treating these lesions in the same
fashion as those that involve the intracranial optic nerve – with excision
of the optic nerve just distal to the optic chiasm to avoid sectioning
through the looping fibers of Willbrand. Patients with an optic glioma and neurofibromatosis type 1
have a better prognosis than those who do not have neurofibromatosis. An
orbital glioma can be removed in two pieces.
The intracranial optic nerve is removed from in front of the chiasm to the
optic canal, and the orbital glioma is removed from the globe to the optic
canal. The residual intracanalicular tumor is then coagulated. By doing
this there is no need to section the annulus or to divide the origin of
the levator and possibly damage the trochlear nerve.
Optic nerve and
chiasmatic tumors: The number of patients reported in the literature is
small; it would appear that long-term survival should be expected in this
group. Surgery is reserved for diagnostic purposes or to excise an
exophytic component: adjunctive therapy is reserved for tumor progression.
tumors: These tumors show markedly varying capacity for progression with
some remaining indolent while others rapidly increase in size. Operative
debulking of the tumor mass with or without adjuvant therapy is utilized
in cases of tumor progression. Although long-term survival has been
reported with these tumors, this is usually accompanied by significant
morbidity. CSF diversion is frequently required.
In patients without
visual compromise with large tumors filling the third ventricle, a
transcallosal approach to the tumor using a subchoroidal approach to the
third ventricle has been a very useful technique for removing large
volumes of tumor. In some cases the biological effect of resecting these
tumors can lead to its stabilization or even involution and occasionally
to complete disappearance. Patients with an optic glioma and
neurofibromatosis type 1 have a better prognosis than those who do not
The role of adjuvant
therapy in the treatment of optic pathway tumors remains controversial.
The young age of the patients considerably limits the use of radiotherapy
but none the less, for posterior tumors, irradiation may be effective in
adults with a 75% 10 year relapse-free survival. Side-effects of radiation
therapy include endocrine dysfunction, secondary malignancy and an
increased risk of developing moyamoya phenomenon especially in the setting
of NF-1. This is particularly true in children younger than 5 years of
age. Patients with an optic glioma and neurofibromatosis type 1 have a
better prognosis than those who do not have neurofibromatosis.
Of the chemotherapeutic
agents available, the nitrosourea-based cytotoxic regiments have been
shown to result in symptomatic improvement or stabilization. Certainly,
there is a role for chemotherapy in those patients with progressive
disease who are too young to receive radiotherapy. Good outcome have been
reported with chemotherapy. Patients with an optic glioma and
neurofibromatosis type 1 have a better prognosis than those who do not
have neurofibromatosis. More recently, carboplatin has been reported to be
effective in arresting growth in progressive optic gliomas but a larger
trial is required to substantiate this.