This tumors, occur more frequently during childhood and adolescence. In 85 percent of cases, it appears before the age of 15 years ( average 3.5 ) and is twice as frequent in girls as in boys (1). Optic pathway gliomas occur with a frequency of 15 per cent among patients with Neurofibromatosis type I (von Recklinghausen disease ).
The tumors may be solid, gelatinous or cystic. Tumors may appear as fusiform enlargement of the optic nerve, with the secondary involvement of the chiasm, or may envelop primarily the chiasm and spread secondary to the optic nerve or into the hypothalamus. “Skip”lesions, or segmental nodules of glioma, may also be seen along the optic pathway. The microscopic appearance is that of a low-grade astrocytoma with simple bipolar, pilocytic astrocytes, and numerous Rosenthal’s fibers.. Evidence of malignancy is extremely unusual in children but has been described in adult. Malignant transformation of optic gliomas is uncommon.(2). Optic gliomas arise and, surprisingly, remain confined within a segment and do not extend along the entire length of the fibers from the retina to the geniculate body. They expand locally within the segment of origin and grow slowly over a period of many years and can attain a considerable size (3). When the tumor is restricted to the optic nerve, they virtually all occur in patients with Neurofibromatosis type I ( NF-I )(4).
Computed tomography ( CT ) and magnetic resonance imaging ( MRI ) provide the accurate localization and the possibility of diagnosis. Optic gliomas are usually isodence, and may are enhanced by intravenous contrast material, especially the more posterior lesions. Calcifications have been described in lesions that involve the optic tract. There is seldom a need for plain skull X-ray films , with classically demonstrate a J-shaped sella; optic foramina views showing an optic foramen > 7.0 mm or a difference of more than 2.0 mm between the left and the right foramina.(2)
The optic pathway gliomas classification is based on their specific location. Type I-A is retrobulbar ( intra-orbital ); type I-B is retrobulbar ( intra-foramina ); in type II the glioma is in optic tract; type III-A is chiasmal and unilateral;type III-B is chiasmal and bilateral. The type III ( A and B ) can involve the hypothalamus (3).
The clinical presentation depends on the type. Tumors of the optic nerve commonly present in childhood, with proptosis ( orbital mass ), visual loss, papilledema or optic atrophy. The proptotic eye is displaced downward and outward. In the very young, visual loss may be manifested by strabismus, nystagmus, or both. Papilledema is seen more often than optic atrophy and is probably due to perineural venous obstruction. Tumors that involve the optic chiasm and the posterior optic nerve present more commonly with optic atrophy than with papilledema. Loss of visual acuity is not so profound as with tumors that involve the nerve more anteriorly, but a visual field deficit can usually be identified in both eyes ( bilateral field defects of homonymous or heteronymous ). Gliomas that originate primarily from the chiasm and extend posteriorly and superiorly into the hypothalamus present with symptoms and signs of increased intracranial pressure as well as hypothalamic dysfunction ( infantilism, adiposity, polyuria, somnolence, and genital atrophy ). Increased intracranial pressure is caused by hydrocephalus secondary to occlusion of the foramina of Monro (2) . Optic pathway gliomas may 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 inevitable leads to the patients death. Rarely the malignant glioma can occurs in children. The mean interval until death in these malignant gliomas is short, being in the range of 8 months (4)
Differential diagnosis : The differential diagnosis depends on the location too. See the table for this information .
______________________________________________________________ Optic nerve glioma Hemangioma Lymphoma Rhabdomyosarcoma Metastases Neuroblastoma Leukemia Ewing’s sarcoma Fibrous dysplasia Panarasal mucocele Meningioma Neurofibromatosis Orbital Neurofibroma Congenital defect in sphenoid bone Optic nerve and chiasm glioma Germinoma Sarcoidosis Optic chiasm glioma extending into the hypothalamus Pituitary adenoma Craniopharyngioma Malignant astrocytoma Epidermoid and dermoid tumors Chordoma Colloid cyst Fibrous displasia Sarcoidosis Histiocitose X Tuberculous Granuloma Hemangioendothelioma ______________________________________________________
The treatment is surgical excision or radiation, depending on the exact location. Optic gliomas limited to the intraorbital or intracranial optic nerve that do not include the chiasm and are associated with loss of vision are resected. In child with visual acuity or in the child with neurofibromatosis , the surgeon and family may wish to observe the lesion with careful follow-up by clinical examination ( visual acuity and fields ) and by MRI or CT at 6-month intervals. Children with optic glioma confined to the chiasm should be observed carefully every 6 months for clinical or radiographic evidence of progression. Radiation therapy is reserved for patients with documented progression (2). Once surgery is determined to be necessary, the subfrontal transcranial approach to the intracranial, intracanalicular, and intra-orbital portions of the optic nerve is the procedure of choice (5)
Optic pathway gliomas have been considered benign and self-limiting. However, most series report significant morbidity and mortality, especially with the more extensive posteriorly placed tumors. Most patients with these tumors survive for many years. Since their course may vary widely, individualization of their care is necessary.
( 1 ) Adams & Victor. ‘ Glioma of the Optic Nerves and Chiasm ‘. Mc Graw Hill, fifth edition, 1993; chapter 31, pages 587 - 8.
( 2 ) Dennis L. Johnson, MD., and David C. Mc Cullough, MD. ‘ Optic Nerve Glioma and other Tumors Involving the Optic Nerve and Chiasm ‘ , in cheek : Pediatric Nerosurgery - Surgery of the developing Neurvous System . Saunders Company, third edition, 1994, pages 409 - 17.
( 3 ) M. G. Yasargil. ‘ Optic Gliomas ‘ , in Microneurosurgery , in 4 volumes. Thieme, First edition, New York, volume 4B, pages 224 - 33.
( 4 ) H. J. Hoffman. ‘ Optic Pathway and Hypothalamic gliomas in Children ‘, in Youmans - Neurological Surgery. Saunders Company, Fourth edition, volume 4, pages 2521 - 9.
( 5 ) Willian H. Sweet & Juan M. Tavera. ‘ Optic Gliomas : Their Diagnosis, Capacity for Spontaneous, Regression, and Radical Surgical Treatment. ‘ In, Operative Neurosurgical Techniques - Indications, Methods, and Results. Saunders C mpany, Third edition, 1995, volume one, pages 253 - 80.
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