Chapter 31

Optic Nerve Pathway Gliomas and Optic Nerve

Meningiomas

Sonali Singh and Jade S. Schiffman

Abstract Optic pathway gliomas are intrinsic slow-growing brain tumors that are the most common primary neoplasms of the optic pathways. Optic pathway gliomas are associated with neurofibromatosis type 1; the incidence of optic nerve glioma in patients with this syndrome varies from 8% to 31%. Sporadic optic pathway gliomas present with visual symptoms, the most common of which is decreased visual acuity, but only half of patients with syndromic tumors develop tumor-related signs or symptoms. The optimal treatment of optic pathway gliomas is controversial; options include observation; surgery with clear margins; radiotherapy; and chemotherapy. In general, optic pathway gliomas tend to be low grade and slow growing and associated with long patient survival. Optic nerve sheath meningiomas represent 1% to 2% of all meningiomas and are seen in approximately one quarter of patients with neurofibromatosis type 2. Only 10% of optic nerve sheath meningiomas are primary (arising from the arachnoid villi surrounding the intraorbital or intracanalicular portions of the optic nerves); the remaining 90% are secondary (arising intracranially). The hallmark of optic nerve sheath meningiomas is slowly progressive vision loss. Treatment is conservative, because these tumors usually grow very slowly. Meningiomas are compatible with good vision for many years and are not life threatening.

31.1 Optic Pathway Gliomas

Optic pathway gliomas (OPGs) are intrinsic slow-growing brain tumors that are the most common primary neoplasms of the optic pathways. These tumors represent 1% of all brain tumors and up to 5% of all brain tumors in children [1]. OPGs can arise anywhere in the optic pathway and are typically described by locations, from

S. Singh (B)

Department of Ophthalmology, Veterans Hospital, Temple, TX, USA e-mail: sonalis25@gmail.com

Oncology Series 6, DOI 10.1007/978-1-4419-0374-7_31,

C Springer Science+Business Media, LLC 2011

just behind the globe, through the chiasm, optic tracts, and hypothalamus, all the way to the geniculate body. Some of these tumors originate in the walls of the third ventricle and infiltrate optic pathways anteriorly and laterally; others arise in the chiasm and infiltrate the hypothalamus posteriorly. Tumors confined to the optic nerve and/or chiasm are categorized as anterior OPGs while tumors that extend beyond the chiasm to the hypothalamus and/or optic tracts are defined as posterior OPGs [2]. There have been case reports of OPGs involving the optic radiations in addition to the pregeniculate optic pathways [3].

The most common syndrome associated with OPG is neurofibromatosis type 1 (NF1) (see Chapter 34). The reported incidence of NF1 among patients with optic nerve or chiasmal gliomas ranges from 10 to 70% while the remaining are sporadic. The incidence of optic nerve glioma in patients with NF1 varies from 8 to 31% [4]. There are rare case reports associating OPG with other syndromes like Turcot syndrome (familial intestinal polyposis and primary neuroepithelial tumors). OPGs have been reported in patients with hybrid phacomatosis, for example, the combined disease of both NF1 and tuberous sclerosis.

In the following discussion of OPGs, we highlight differences between sporadic and syndromic tumors.

31.1.1 Demographics and Presentation

Patients with OPG may be asymptomatic or may present with symptoms that vary depending on the location. Patients with an optic glioma of the optic nerve within the orbit often present with slow, painless, unilateral visual loss, optic disc swelling and/or atrophy, proptosis, and strabismus. Rarely patients with optic nerve gliomas may develop a central retinal vein occlusion, iris rubeosis with neovascular glaucoma. Patients with more posterior intracranial gliomas involving the hypothalamic/third ventricle/optic chiasmal region can present with bilateral visual loss, endocrine/hypothalamic disturbance, spasmus nutans, and obstructive hydrocephalus [5].

NF1-associated OPG is more common in females and presents at an earlier age compared with sporadic OPG. Sporadic OPG presents with visual symptoms, while only half of the patients with syndromic OPG ever develop signs or symptoms related to the OPG. Therefore, a significant number of patients with NF1 may have an asymptomatic OPG. In symptomatic OPG, decreased visual acuity is the most common clinical feature with greater incidence among patients with sporadic OPG.

On ophthalmological examination, optic atrophy has been reported as the most common manifestation in sporadic as well as syndromic OPG; however, optic disc edema, optociliary shunts, relative afferent pupillary defects, and visual field defects may also present.

Exophthalmos is more common in NF1 patients while features of raised intracranial pressure are more likely to occur in patients with sporadic OPG [1]. Grill et al. [6] found that in their series of cases, proptosis was significantly more frequent in

patients with NF1 (21.5%) than in those without (5.5%), whereas patients without NF1 were more likely to present with nystagmus and hydrocephalus [6].

31.1.2 Histopathology

OPGs are typically low-grade juvenile pilocytic astrocytomas, although fibrillary astrocytomas have been reported. Pilocytic astrocytomas have a biphasic pattern with characteristic Rosenthal fibers and eosinophilic granular bodies. Pilomyxoid astrocytomas are a relatively new group of OPGs which demonstrate piloid cells in a loose fibrillary myxoid background and lack Rosenthal fibers and rarely show eosinophilic granular bodies. Pilomyxoid astrocytomas present at an earlier age than pilocytic astrocytomas and have more aggressive behavior.

OPG can exhibit either a perineural or an intraneural growth pattern. Patients with NF1 are more likely to have perineural pattern, whereas patients without NF1 predominantly have an intraneural growth pattern [5].

31.1.3 Imaging and Lesion Location

Lesions in patients with the sporadic form predominantly have a chiasmatic location and are cystic in morphology and deform the normal shape of the optic nerve pathways, while patients with NF1 have gliomas most commonly located in the orbital optic nerve although they may continue intracranially. They rarely have a cystic component and have no effect on the shape of the optic nerve. Cystic morphology is clinically significant, accounting for more than 50% of the tumor size in patients with cystic OPGs. The larger tumor size in the sporadic group is probably responsible for the symptomatic status of these patients compared with syndromic patients.

Patients with the sporadic form commonly have gliomas that extend beyond the optic pathways and cause hydrocephalus [1].

Computerized tomography (CT) demonstrates enlargement of the optic nerve or chiasm which has imaging characteristics as isodense with the normal brain. Contrast enhancement is variable, from imperceptible to moderate, but generally less than with optic nerve sheath meningiomas. Typically optic nerve gliomas show a well-outlined, fusiform enlargement of the optic nerve (Fig. 31.1), but occasionally it may be more rounded or even multilobular. Chiasmal lesions appear as an enlargement of the chiasm or as a suprasellar mass (Fig. 31.2), occasionally with a cystic component, and are seen best on coronal images. Cystic spaces within the lesion usually correspond to areas of mucinous accumulation. Calcification is rare and can differentiate the intraaxial OPGs from optic nerve meningiomas, which frequently calcify. Chiasmal glioma can rarely calcify [7].

Although CT is excellent for orbital optic glioma, magnetic resonance imaging (MRI) has proven to be superior to CT for imaging optic nerve glioma

Fig. 31.1 MRI glioma optic nerve OD: (a) axial and (b) coronal

Fig. 31.2 MRI glioma optic chiasm: (a) axial and (b) coronal

posterior extension, including involvement of the intracanalicular portions of the nerve, because of elimination of bone artifacts. MRI is superior to CT for evaluation of chiasmal, hypothalamic, and optic tract lesions due to improved contrast enhancement resulting from subtle differences in fat contents and hydration of neural tissues [8].

On MRI, gliomas show normal to slightly prolonged T1 relaxation times which image isointense to slightly hypointense to cerebral white matter on T1-weighted sequence while areas of necrosis or mucinous degeneration are hypointense. The T1 image is best for characterization of tissue composition. The T2 relaxation time is prolonged, giving gliomas a hyperintense image on T2-weighted sequence. This