Optic Nerve Sheath Meningioma Workup

Updated: May 11, 2021
  • Author: Mitchell V Gossman, MD; Chief Editor: Edsel B Ing, MD, PhD, MBA, MEd, MPH, MA, FRCSC  more...
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Imaging Studies

Plain radiographs usually are not diagnostic, unless end-stage enlargement of the optic canal or hyperostosis is present.

  • CT scan with contrast is an excellent imaging technique for evaluation of optic nerve sheath meningioma (ONSM).

    • Thin slices (1.5-3 mm) must be taken to assess the extent of the tumor. ONSM is confined to the dura mater; therefore, it often appears as a distinct, fusiform thickening of the optic nerve. This enlargement may appear as localized or as an eccentric expansion of the optic nerve, and it occurs most commonly at the orbital apex.

    • ONSMs usually enhance homogeneously. In addition, linear, diffuse, or patchy calcifications within or along an optic nerve mass are commonly seen. [11]

    • Meningiomas surround the optic nerve. The diameter of the nerve is attenuated within the surrounding mass, giving a bull's eye appearance on coronal images and a tram track appearance on axial images. [11] (With optic nerve glioma, the nerve itself is expanded; there is no bull's eye appearance on coronal section, but a sagittal kinking is often seen.)

    • Although an MRI most readily shows the soft tissue tumor characteristics of ONSM, a CT scan better displays any associated bony hyperostosis.

  • Gadolinium-enhanced fat-suppression, T1-weighted pulse sequences allow visualization of meningiomas as a localized or tubular enlargement with significant contrast enhancement.

    • On most MRI pulse sequences, the tumor appears isointense as compared to the optic nerve and the brain tissue. Compared to the brain tissue, meningiomas may appear hypointense on T1-weighted images and hyperintense on T2-weighted images.

    • Other helpful MRI techniques include enhanced fat-suppression, T1-weighted images. Intraorbital extension of intracranial meningioma can be detected easily with contrast enhanced CT scan or MRI.

  • The exact knowledge of bony involvement in meningiomas is imperative because unresected meningiomatosis bone is one of the important factors that may contribute to recurrence.

    • EPM may be difficult to detect by radiologic evaluation. Plain radiographs may demonstrate hyperostosis, which may be present in up to 44% of patients with EPM.

    • Differential diagnosis includes all lesions that can be associated with focal hyperostosis (eg, osteomas, Paget disease, neurosarcoidosis, tuberculosis, lymphoma, fibrous dysplasia).

  • Standard tomography may demonstrate a thin layer of calcium deposit along the inner table of the hyperostosis bone with a superimposed lucency, which is thought to be dura mater. More invasive radiologic examinations, such as cerebral angiograms, are not of great value. Scintigraphic studies are of limited value.

  • CT scan in EPM often shows hyperostosis when present. Hyperostosis may involve the outer and inner tables with surface irregularity. With contrast, enhancement of the meninges may be seen in the area underlying the hyperostosis.

  • MRI without enhancement is not superior to CT scan. Both CT scan and MRI may show minimal parenchymal edema. Plaques are usually not visualized with either imaging technique.

    • Gadolinium may be helpful to demonstrate meningeal enhancement on T1-weighted sequences.

    • For suspected cases of juxtaorbital meningiomas, thinner slices of the orbit (3 mm) with T1-weighted MRI pulse sequence of the orbit are needed to improve the subtle contrast enhancement around and within the orbit.

    • Postcontrast fat-suppression, T1-weighted MRI images in axial and coronal planes also are useful because fat-suppression allows better visualization of the gray scale. At present, this technique is the best available imaging tool for the correct diagnosis of EPM.

      Meningioma of the orbit. Axial sequence on T1-weig Meningioma of the orbit. Axial sequence on T1-weighted MRI with gadolinium that shows enhancing lesion of the orbit causing proptosis and en plaque invagination laterally around the temporal pole and medially above the ethmoid sinus.
      Meningioma of the optic nerve sheath. Coronal sect Meningioma of the optic nerve sheath. Coronal section of T1-weighted MRI of the orbits that shows a left orbital mass lesion occupying most of the orbital lumen, diffusely enhancing with gadolinium.

Histologic Findings

Historically, the classification of meningiomas has been based upon cell shapes, cell patterns, and cell products. The macroscopic appearance of meningiomas may be hemispheric, bun-shaped, or globular, and they may vary in gross appearance as epithelial or mesenchymal. They usually are attached to the dura and invaginate into adjacent neural structures. Enveloped in a thin capsule derived from the adjacent meninges, they remain extraaxial and are separated easily from the brain or the spinal cord.

According to the World Health Organization (WHO) in 1993, 3 different types of meningiomas exist based on malignant behavior, as follows:

  • Benign (grade I) with a recurrence rate of 6.9%: Despite invasion of the adjacent bony structures, grade I meningiomas do not invade the brain parenchyma.

  • Atypical (grade II) with a recurrence rate of 34.6%: This type of meningioma shows frequent mitosis and an increased nuclear-cytoplasmic ratio.

  • Malignant (grades III and IV) with a recurrence rate of 72.7%: This type shows even greater mitosis, necrosis, and invasion of brain parenchyma.

Malignant transformation is rare. Originally, malignancy was seen in anaplastic tumors, but they may arise from any of the meningioma variants or atypical meningiomas. Papillary histopathology is associated with local aggressiveness and increased incidence of late distant metastasis. The papillary type is considered malignant by definition and is encountered more frequently in children.

Earlier classification schemes used the term angioblastic meningioma for what is now considered to be a hemangiopericytoma. This neoplasm is distinctly separate from a meningioma, and it shows extremely high propensity for recurrence and metastasis. Hemangiopericytoma is a sarcoma in the new WHO classification.

Growth type classification of meningiomas according to cell type is as follows:

  • Meningothelial growth is characterized by lobules of cells, marginated chromatin, and pseudoinclusions (ie, invagination of cell and nuclear membrane).

  • Fibroblastic growth is characterized by spindle-shaped cells in parallel interlacing bundles, intercellular collagen, and reticulin.

  • Transitional growth shows mixed features of the other 2 categories, and it commonly includes whorls and psammoma bodies usually not present in the other 2 types. Cell type is not indicative of expected behavior of the tumor.