Clinical History
Location, age of the patient, visual disturbance and imaging findings are suggestive for optic nerve glioma.
Imaging Findings
The patient presented with proptosis and decreased vision of the right eye, without pain.
Ophthalmologic examination showed a considerable limitation of visual acuity and a slight reduction of eye movement on the right side.
Contrast enhanced CT scan of the orbits (not shown) demonstrates an heterogeneously enhancing intraconal mass, displacing the extra-ocular muscles, no visualization of the optic nerve, and extending into the orbital apex.
MRI of the orbits demonstrates on the axial SE T2-weighted image a mass of high signal intensity containing several small, hypo-intense areas, causing anterior displacement of the ocular bulb.
Axial fat-suppressed Gd-enhanced T1-weighted image shows pronounced enhancement of the mass, with hypo-intense areas. Intratumoral, linear signal void corresponding to vascular structure is also seen.
Arteriography of the right internal carotid artery visualizes kinking and bowing of the ophthalmic artery around a mass of 2 cm in diameter containing pathologic vessels. Extensive venous drainage to the facial vein is noted.
Location, age of the patient, visual disturbance and imaging findings are suggestive for optic nerve glioma. This diagnosis was histologically confirmed after resection of the tumor.
Discussion
Optic nerve gliomas are well-differentiated, slowly growing intraconal tumors, with predilection for children in the first decade of life. If both optic nerves are involved, the diagnosis of neurofibromatosis type I is very likely. Optic nerve gliomas have a benign juvenile pilocytic histology.
Clinically, optic nerve glioma presents as a low-grade proptosis, impaired vision, visual field obscuration with reduced eye movements, and optic atrophy.
Growth of the tumor usually leads to fusiform enlargement of the optic nerve. CT scan shows a tortuous nerve in which sometimes lucent regions are seen, secondary to tumor necrosis. Enhancement may be absent or moderate.
Gliomas present as well-circumscribed hypo-intense mass lesions on T1-weighted images and as hyper-intense masses on T2-weighted images. Contrast-enhanced is minimal. Contrast-enhanced fat-suppressed T1-weighted SE images are very useful in visualizing the tumor.
Differential diagnosis must be made with rhabdomyosarcoma and orbital pseudotumor.
Rhabdomyosarcoma is the most common orbital malignancy in children. Its MRI characteristics are almost the same as in glioma, but these tumors present as highly aggressive soft tissue masses, with extension into the paranasal sinuses or cranium, accompanied by bone destruction.
Contrast enhancement as with CT is variable and usually homogeneous in pilocytic gliomas.
Orbital pseudotumor is an idiopathic inflammatory reaction of the optic nerve. It is hypo-intense on T1-weighted images and iso-intense on T2-weighted images. The extraocular muscles are usually involved, although involvement of the retrobulbar fat is also seen. Pseudotumors may appear less well-circumscribed.
Differential Diagnosis List
