Fig. 5.12  (a) Optic atrophy (b) CT scan showing large optic nerve glioma. Note proptosis of globe

5.5.2.2  Optic Chiasmal Glioma

Monocular or binocular but markedly asymmetric nystagmus may be the presenting feature. The nystagmus may be vertical or horizontal and usually consists of fast pendular oscillations of small amplitude. In some cases, the associated head movement may mimic spasmus nutans, a benign and spontaneously remitting disorder of infancy that includes asymmetrical nystagmus, headnodding, and anomalous head positioning [87–89].

5.5.3  Pathophysiology

Optic nerve gliomas are typically benign tumors composed­ of elongated astrocytes with microcystic­ degeneration with the accumulation of mucopolysaccharide material. Rosenthal fibers, which are elongated, irregularly shaped intracellular eosinophilic structures, are typically mixed in the tumor [92]. When limited to the intraorbital compartment, optic nerve gliomas usually remain within the confines of the dura. If the tumor extends through the optic canal into the intracranial compartment, widening of the optic canal occurs.

Optic chiasmal gliomas are more commonly extended along the optic nerves or optic tracts. Gliomas limited to the optic chiasm occur more often in patients who do not have NF-1 [93–95].

These tumors usually grow by local expansion. Two growth patterns have been observed [96]:

1.Circumferential perineural growth: the tumor breaks through the pia mater and grows within the subarachnoid space. The optic nerve becomes progressively compressed and narrowed as the tumor grows around it. This pattern is more commonly observed in patients with NF-1.

2.Expansile intraneural growth: the tumor grows within the core of the optic nerve. The substance of the optic nerve becomes progressively larger as the tumor expands. This pattern occurs more often in patients without NF-1.

Enlargement of benign gliomas of the anterior visual pathways may occur by neoplastic transformation, arachnoidal hyperplasia, cystic degeneration with accumulation of mucopolysaccharide material or intraneural hemorrhage. Rapid deterioration of visual function might occur with cystic degeneration or hemorrhage. Spontaneous improvement of visual function or reduction in tumor size might occur by resorption of mucinous material.

5.5.4  Incidence

Benign optic gliomas of childhood account for less than 5% of all intracranial pediatric tumors [97]. This condition is identified in 15–19% of unselected children with NF-1 who undergo CT or MI imaging. Only one third of these individuals have abnormal neuro­ -ophthalmologic signs; the remainder are asymptomatic [98, 99]. Chiasmal gliomas are roughly 3 times more common than optic nerve gliomas [86].

Chiasmal gliomas, however, appear to have a worse prognosis for survival than do patients with optic nerve gliomas. The overall mortality rate is influenced by the presence or absence of intraparenchymal extension [86].

The behavior of these tumors is unpredictable [100]. Exceptions include regional and leptomeningeal dissemination along the neuroaxis [91, 101, 102], intraperitoneal metastases through ventriculoperitoneal shunts [103, 104] as well as spontaneous regression of tumor mass [105] associated with improvement of visual function. These reports argue for close observation.

5.5.6  Diagnosis

CT and MR imaging have revolutionized the diagnostic approach to patient with these tumors. On high-­resolution CT, optic nerve glioma typically appears as a well-demar- cated fusiform enlargement of the optic nerve [106] (Fig. 5.12b). Kinking or tortuosity is often observed. The CT density of the tumor is similar to that of the brain. Compared to meningiomas, optic nerve gliomas often demonstrate less enhancement following administration of contrast material. Calcification is rare. Optic chiasmal gliomas are well circumscribed [107] and usually enhance with contrast material (Fig. 5.13). Calcification within chiasmal gliomas is observed more often than with optic nerve gliomas. On MR imaging, tumor involvement of the optic tract can be visualized with far greater sensitivity than when using CT. Gliomas of the anterior visual

5.5.5  Natural History and Prognosis,

i.e., Signs, Symptoms, Timing, etc.

Optic nerve gliomas generally grow slowly and are associated with a favorable prognosis for long-term survival. Dutton [86] reviewed the clinical course of more than 300 patients from published series and determined that only 21% of those with untreated or partially resected optic nerve gliomas showed recurrence or progression during a mean follow-up period of 10 years. Most relapses occurred during the first few years of follow-up.

Fig. 5.13  CT scan of bilateral optic nerve gliomas. Note contrast enhancement with surrounding proliferation. “Kinking” of the nerve is seen on the left

pathway are isointense or slightly hypointense relative to brain on T1-weighted sequences and hyperintense using T2-weighted sequences [108, 109]. Tumor enhancement following administration of contrast is usually greater than that of postcontrast CT images.

Gliomas in patients with NF-1 have some specific characteristics including: bilateral optic nerve gliomas [94], the circumferential/perineural growth pattern [110, 111], and elongation and kinking of the intraorbital optic nerve [112]. For some NF-1 patient, despite initial normal MR imaging, the risk of developing an anterior visual pathway glioma exists up to the age of 6 years [113, 114].

5.5.7  Treatment

The management remains highly controversial. The effect of radiation therapy is not conclusive. There are no randomized trials to compare the outcomes of treated and untreated patients. Alvord and Lofton [100] studied patients with optic nerve and chiasmal gliomas treated with radiation. Patients receiving greater than 4,500 cGy in general do better than those receiving less than 4,500 cGy. Among 33 patients with optic nerve gliomas treated primarily with radiation using varying doses, the 20-year mortality rate was 14% for those treated with unreported doses and 0% for those treated with doses greater than 4,500 cGy. For optic chiasmal gliomas, the 20-year mortality rate for patients who received doses greater than 4,500 cGy was 60% in the presence of hydrocephalus and 52% in its absence. This rate is similar to those with untreated tumors. In terms of visual outcome, some reports showed surprisingly good results, and others reported no positive influence [115–117]. Overall, radiation therapy may provide some short-term benefit for large exophytic chiasmal gliomas although long-term positive effect for survival and visual function has not been adequately demonstrated. Currently, the relative indications for using radiation therapy are shown in Table 5.6 [118].

The potential benefit of radiation therapy must be balanced by the consideration of long-term complications of the treatment in the pediatric patients [116, 119] (Table 5.7).

Chemotherapy is an alternative option for pediatric patients with gliomas of anterior visual pathway when radiation therapy is not effective or the potential risk to the young brain is too great. The regimens include:

1.Vincristine with either actinomycin D or carboplatin: for patients under age of 5 years with newly diagnosed optic chiasmal gliomas and in patients of any age with progressive tumor enlargement of loss of vision [120–122].

2.Vincristine with intravenous etoposide: for newly diagnosed or recurrent tumors [123].

3.Vincristine with oral etoposide: for recurrent tumors after initial treatment using other chemotherapeutic agents or radiation [124].

Hematologic and systemic toxicity are infrequent and mild.

The neurosurgeon’s role in diagnosis and management of optic nerve gliomas is limited. The age of most affected individuals, the slow growth, and the characteristic neuroimaging findings are sufficient to exclude most other inflammatory, infectious, and infiltrative

Table 5.6  Indications for treatment of optic nerve/chiasmal gliomas

Bilateral optic nerve gliomas associated with progressive loss of vision and documented growth using MR imaging

Unilateral optic nerve glioma with progressive loss of vision and MR imaging-documented extension into the intracranial cavity

Intrinsic chiasmal glioma that has progressed after a period of observation or following the use of chemotherapy

Chiasmal glioma associated with exophytic brain extension into the hypothalamus or third ventricle

Chiasmal glioma associated with severe visual loss upon diagnosis

Table 5.7  Complications of radiation therapy

Neurobehavioral

 Intellectual impairment

 Learning disabilities

 Behavioral disorders Endocrine

 Growth failure

 Precocious puberty

 Diabetes insipidus

 Amenorrhea

 Panhypopituitarism Cerebrovascular

 Radiation vasculopathy

 Moyamoya syndrome (increased in patients with NF-1)

opticneuropathiesformfurtherconsideration.Biopsying the tumor for confirmation may result in further symptomatic loss of vision. The one rare diagnostic consideration, which may benefit from biopsy, is to differentiate glioma from primary optic nerve sheath meningioma (ONSM). It may present with the clinical and neuroimaging ­characteristics similar to glioma, and it can behave aggressively in children and young adults [125, 126].

Surgically managing a patient with optic nerve gliomas may be indicated when either the patient’s vision deteriorates to a useless level or intracranial extension of the tumor is documented using MR imaging. At that point, a complete excision offers patients the best overall outlook for survival. When an optic nerve glioma is completely excised and the intracranial margins are free of tumor, the 10-year survival rate is 100% [86]. Other relative indications for surgical intervention are primarily for alleviating ocular complications such as severe pain and/or proptosis.

For optic chiasmal gliomas, when large exophytic components make it impossible to distinguish whether the tumor is intrinsically associated with the optic chiasm or represents a large suprasellar/hypothalamic mass consuming the chiasmal by extrinsic growth, it is reasonable to perform a craniotomy for diagnosis to rule out germinoma or craniopharyngioma [97]. There are no randomized studies on the outcomes of patients undergoing partial resection. Retrospective surveys do not indicate any long-term benefit for patients after partial resection. Currently, medical management is the primary treatment for most patients. Up to 40% of patients who have chiasmal gliomas with large exophytic mass develop hydrocephalus [84, 85, 127]. The indication for intraventricular shunt placement is similar­

to those used for children with obstructive hydrocephalus associated with other malignancy.

the ophthalmologist, the neurooncologist, and social worker must communicate on a regular basis about the patient’s condition. Detecting change can be difficult, especially if vision is already significantly compromised. At least, semiannual MRI scans and exams are usually indicated early in the course to monitor the tumor’s activity. Depending on the family’s resources and proximity to specialized care, this, by itself, can be a significant intrusion. Involvement of support agencies, social workers, and other individuals can help smooth the way for these patients.

In patients with unilateral optic nerve gliomas, proptosis can be disfiguring. If visual function is preserved, the patient is faced with a dilemma. Retain the eye with its ugly appearance, or sacrifice it and lose the sight. Sometimes, orbital expansion procedures similar to those used for thyroid patients can help.

Patients with bilateral gliomas often have severely reduced vision and will need the assistance of visually impaired teachers and schools. Referrals should be made early even if good vision is present since visual loss can progressively worsen.

5.6  Optic Nerve Sheath

Meningioma (ONSM)

5.6.1  Introduction

ONSMs are the second most common optic nerve tumor but represent only 1% of all meningiomas. They produce slowly progressive visual acuity loss, dyschromotopsia, and visual field defects. Mild proptosis (Fig. 5.14) and disc edema are early signs. The classic diagnostic triad is visual loss, optic atrophy, and ciliary shunt vessels.

5.5.8  Social and Family Impact

The variable presentations and clinical course result in a wide variety of responses to this disorder. For many, it is a nuisance, with stable vision and minimal symptoms. For others, it can be a scary and stressful condition, fraught with uncertainty coupled with the fear of eventual blindness or even death. Support groups can be very helpful in assisting families having to cope with this disorder. A multidisciplinary approach is necessary to adequately care for patients. At a minimum,

Fig. 5.14  Patient with an optic nerve sheath meningioma of the left eye. Note proptosis