Fig. 10.1
Right optic neuritis. (a) Coronal T1-weighted image demonstrates the right optic nerve expansion compared to the left. (b) Coronal, short time inversion recovery (STIR) image demonstrates increased signal in the right optic nerve. (c) Coronal, fat-suppressed, postcontrast MRI image demonstrates significant enhancement in the right optic nerve, with mildly coarse margin
10.1.4 Comments
If young and middle-aged patients present with acute vision decline and MRI shows segmental hyperintensities in the optic nerve, enhanced obviously postgadolinium, then optic neuritis is indicated. Meanwhile, intracranial and intraspinal exams should be done to see if multiple sclerosis or optical neuromyelitis is suggested.
10.2 Optic Nerve Glioma
10.2.1 Pathological Characteristics
- 1.
Optic nerve glioma, originating from the glial cells in the optic nerve, is a kind of benign or low-grade malignant tumor.
- 2.
According to the age of onset, optic nerve glioma can be classified into two categories: the childhood optic nerve glioma and the adult optic nerve glioma. The former is more common and is mostly pilocytic astrocytoma. The adult form is very rare and usually aggressive.
- 3.
The section of the lesions often appears white. The optic nerve is enlarged, surrounded by arachnoid tissues with different thicknesses, which are covered with tight dura mater.
10.2.2 The Choice of Imaging Modality
- 1.
CT: If the patient presents related ocular symptoms and clinical examination shows retrobulbar disease, CT is often the first investigation performed.
- 2.
MRI: Once the CT scan reveals a mass image in the optic nerve area, MRI can be further performed to clarify the nature of the lesions, involving the origin and scope.
10.2.3 Imaging Findings
- 1.
CT findings: CT scan usually reveals a soft-tissue mass in the optic nerve area, with homogeneous density, consistent with the long axis of the optic nerves (Fig. 10.2a, b). If the medial segment of the optic canal is involved, then optic canal enlargement can be seen.
- 2.
MRI findings: On T1-weighted images, optic nerve gliomas are usually homogeneous hypointense (Figs. 10.2c and 10.3a), and on T2-weighted images homogeneous hyperintense (Figs. 10.2d and 10.3b). Sometimes the subarachnoid space around the optic nerve can be seen widened and expanded because of tumor compression, and the lesions are enhanced to varying degrees, from non-enhanced to significantly enhanced (Figs. 10.2e and 10.3c, d). The optic canal-involved and intracranial lesions may demonstrate a dumbbell-like appearance (Walrath et al. 2008).
Fig. 10.2
Optic nerve glioma. (a) Cross-sectional CT soft-tissue window shows that the lesion in the right orbit, along the optic nerve, appears isodense. (b) Oblique sagittal CT soft-tissue window shows that the lesion is along the optic nerve and rodlike. (c) Cross-sectional T1-weighted MRI shows that the lesion in the right orbit is relatively homogeneous hypointense, pressing the back part of the eyeball. (d) Cross-sectional T2-weighted MRI shows that the lesion is homogeneous hyperintense. (e) Cross-sectional, fat-suppressed, postcontrast MRI image reveals intense homogeneous enhancement of the lesion
Fig. 10.3
Optic nerve glioma. (a) Cross-sectional T1-weighted MRI reveals an isointense mass along the optic nerve area. (b) Cross-sectional T2-weighted MRI shows a hyperintense lesion. (c) Cross-sectional, fat-suppressed, postcontrast MRI image reveals a lesion significantly enhanced. (d) Oblique sagittal, postcontrast MRI images demonstrate that the lesion grows along the optic nerve
10.2.4 Comments
The diagnosis of optic nerve glioma should be considered in any patient presenting with relevant symptoms when CT shows a mass along the optic nerve area. MRI is further performed to assess the range of the lesion and to help confirm the diagnosis.
10.3 Optic Nerve Sheath Meningioma (ONSM)
10.3.1 Pathological Characteristics
- 1.
ONSMs arise from the optic nerve arachnoid fibroblasts or endothelial cells on the inside of the dura. It is mostly benign, and few can be malignant.
- 2.
ONSMs appear light red, with no capsule. The tumor typically has a smooth contour.
10.3.2 The Choice of Imaging Modality
- 1.
CT: If the patient presents related ocular symptoms and clinical examination shows retrobulbar disease, CT is often the first investigation performed.
- 2.
MRI: Once the CT scan reveals a mass image in the optic nerve area, MRI can be further performed to clarify the nature of the lesions, involving the origin and scope.
10.3.3 Imaging Findings
- 1.
CT findings: On CT, ONSM appears as a mass along the optic nerve in isodensity just as soft tissue (Fig. 10.4a, b), and about 20% of mass shows linear or sheetlike calcification. Coronal CT shows an annular hyperdensity image surrounding the optic nerve. If the intracanalicular portion of the optic nerve is involved, the optic canal widening and bony hyperostosis can be seen.
- 2.
MRI findings: The tumor appears iso- to hypointense on T1-weighted images (Figs. 10.4c and 10.5a), and iso- to hypointense on T2-weighted images (Figs. 10.4d and 10.5b). The lesion is enhanced with gadolinium whereas the optic nerve is not, resulting in the typical “double-track sign” (Fig. 10.5c) and “cuff sign” (Figs. 10.4f and 10.5d). Enhanced MRI can also show if the lesion involves the intracranial tissue backward through the optic canal.
Fig. 10.4
Right optic nerve sheath meningioma. (a) Cross-sectional CT soft-tissue window shows that the tumor, displacing the optic nerve laterally, is usually isoattenuating to the soft tissue. (b) Coronal CT soft-tissue window shows that the optic nerve is encased by the tumor and the boundary is not clear. (c) Cross-sectional T1-weighted MRI shows that the tumor is isointense and has a smooth contour. (d) Cross-sectional T2-weighted MRI shows that the mass is isointense and homogeneous. (e) Cross-sectional, fat-suppressed, postcontrast MRI image reveals that the tumor, significantly enhanced, surrounds the optic nerve. (f) Coronal, fat-suppressed, postcontrast MRI image shows the enhancing tumor around the non-enhancing optic nerve (arrow), appearing as the “cuff sign”
Fig. 10.5
Left optic nerve sheath meningioma. (a) Cross-sectional T1-weighted non-enhanced MRI shows that the isointense fusiform tumor grows backward along the optic nerve in the left orbit. (b) Cross-sectional T2-weighted MRI shows the mass is isointense and homogeneous; (c) Cross-sectional, fat-suppressed, postcontrast MRI image shows the enhancing tumor surrounding the non-enhancing optic nerve, resulting in the “double-track sign.” (d) Coronal, fat-suppressed, postcontrast MRI image reveals the enhancing tumor around the non-enhancing optic nerve (arrow), appearing as the “cuff sign”
10.3.4 Comments
CT findings of a mass with calcification along the optic nerve area generally confirm the diagnosis of the ONSM, but for lesions with no calcification, it is hard to differentiate from the optic nerve glioma.
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