eMedicine Specialties > Radiology > Brain/Spine

Neurofibromatosis Type 2: Imaging

Author: Andrew L Wagner, MD, Assistant Professor of Radiology, Instructional Faculty, University of Virginia School of Medicine; Director of Neuroradiology, Department of Radiology, Rockingham Memorial Hospital
Contributor Information and Disclosures

Updated: Mar 17, 2008

Radiography

Findings

Intracranial abnormalities found in NF2 are not visible on plain radiographs, except in cases of hyperostosis from a meningioma. Widening of the neural foramina and scalloping of the posterior aspect of the vertebral bodies can be seen on plain radiographs of the spine and result from pressure erosion from the schwannomas rather than the dural ectasia that causes the bony malformations in NF1. Scoliosis is also associated with NF2 and can be measured most accurately on plain radiographs, although CT scan studies or MRI may be necessary to evaluate some of the more subtle spinal deformities.

Degree of Confidence

Foraminal widening and posterior vertebral scalloping is not specific for NF2. The dural ectasia of NF1, as well as some bone dysplasias, can cause scalloping of the posterior vertebral bodies similar to that seen in NF2; however, the scalloping in NF2 is a result of associated tumors. Although the scalloping from NF1 and NF2 are occasionally indistinguishable on plain radiographs, either MRI or CT scanning easily distinguishes between the 2.

NF2 is associated with scoliosis, but it is an uncommon cause of scoliosis, and no study has described scoliosis as a presenting sign of NF2.

Computed Tomography

Findings

• CN VIII schwannomas are visualized on CT scans as strongly, but heterogeneously, enhancing cerebellopontine angle masses that extend from the IAC. On precontrast imaging, these schwannomas are isodense to hypodense with respect to brain tissue and may have associated cysts or hemorrhage. The pressure of the tumor often results in widening of the IAC and is best visualized using bone windows. Gas CT cisternography, with 0.5- to 1-mm slices, can demonstrate small tumors within the IAC that are typically missed on routine CT scanning. Small schwannomas of the other CNs are easily overlooked or not visualized because of their proximity to osseous structures and the relatively poor contrast resolution of CT scanning.
• Intracranial meningiomas present as enhancing extra-axial masses, often with internal calcifications and adjacent hyperostosis that are best visualized with bone windows. Adjacent white matter with decreased attenuation is commonly seen when tumors are large, likely representing edema. The persistence of this abnormality for years after the tumor has been resected suggests the likely existence of a demyelinating factor as well. When large enough, meningiomas may exhibit mass effect on the brain parenchyma and can be aggressive at times, invading the adjacent bone. Without contrast, meningiomas may have the same attenuation as the brain, but they typically have higher attenuation values resulting from the presence of calcium and a high nuclear-to-cytoplasmic ratio. Small tumors can be missed, particularly over the calvarium and in the posterior fossa, where beam-hardening artifact is the worst.
• Spinal schwannomas appear either as dumbbell-shaped enhancing masses extending out the neural foramina or as intradural extramedullary masses in the spinal canal. CT scans show widening of the foramina or pressure erosion on the adjacent vertebral body, and sagittal reformatted images are useful.
• Spinal meningiomas are found as intradural extramedullary masses, usually in the thoracic spine. They are best imaged on CT myelography, although they usually show enhancement on contrast CT scans. Occasionally, meningiomas extend into the neural foramina and appear as dumbbell-shaped masses with widening of the neural foramina. In these cases, distinguishing them from schwannomas or neurofibromas is difficult.
• Spinal ependymomas are intra-axial enhancing masses seen most frequently in the cervical cord and conus. When involving the conus or filum, an ependymoma may be pedunculated and appear as an extra-axial mass. Cervical cord ependymomas are well-marginated enhancing tumors that may exhibit associated cyst formation.

Degree of Confidence

Perform CT scanning only in patients with NF2 in whom MRI is contraindicated, because MRI provides superior tumor imaging and characterization. When CT scanning must be used, perform high-resolution techniques in the axial and coronal planes and consider CT cisternography for detecting small tumors. Even when visualized, the type of tumor is often difficult to identify on CT scans, because a large amount of overlap is seen in tumor appearance. CT myelography is adequate in depicting the extra-axial lesions of NF2, but it is relatively poor at detecting ependymomas. CT scanning with 3-dimensional (3-D) volumetric rendering can be useful for preoperative planning in patients with NF2 and associated scoliosis or spinal dystrophy.

Magnetic Resonance Imaging

Findings

CN VIII schwannomas are well-defined masses arising from the IAC and frequently extend into the cerebellopontine angle, demonstrating an ice cream cone or mushroom shape (see Image 1).

• CN VIII schwannomas often have heterogeneous signals, but they are typically isointense to hypointense on T1-weighted images and hyperintense on T2-weighted images.
• High-resolution, heavily T2-weighted sequences have been used to detect small CN VIII schwannomas and appear to be approximately as sensitive as contrast MRI.
• Using this technique, the bright cerebrospinal fluid (CSF) around CN VII and CN VIII is used as a contrast agent, and schwannomas appear as small rounded masses that efface the CSF in the canal.
• This technique is also useful in detecting cochlear involvement by the tumor, because the cochlear turns can normally be easily identified as curvilinear areas of increased signal.

Following contrast administration, CN VIII schwannomas enhance avidly but often heterogeneously, particularly in larger tumors.

Nonenhancing areas of necrosis are often present as the schwannomas enlarge, and associated cysts or blood products from internal hemorrhage may be present.

Other CN schwannomas have a similar MRI appearance and differ only in location, occurring along the paths of the other CNs. The multiplanar capability of MRI is particularly useful in distinguishing a CN schwannoma from a meningioma adjacent to a nerve.

Meningiomas in NF2 have the same distribution and signal characteristics as spontaneous meningiomas, occurring most frequently along the falx and over the convexities (see Image 2).

• Meningiomas are extra-axial tumors and thus demonstrate cortical buckling and a CSF cleft.
• A confluent area of white matter with increased T1 signal and decreased T2 signal may be seen in the adjacent brain parenchyma and likely results from a combination of vasogenic edema and demyelination.
• Meningiomas typically are isointense with gray matter on all sequences and, when small, can be difficult to detect without contrast.
• Signal intensity can vary, and almost any combination of T1 and T2 signals can be seen.
• Cyst formation is uncommon, but calcification occurs frequently and can cause the tumor to appear heterogeneous.
• Following gadolinium administration, intense and generally homogeneous enhancement is seen, and a dural tail of enhancing dural tissue is often found extending from the tumor's dural attachment, although this is not specific for meningioma.^27,28
• Meningiomas in patients with NF2 may be more aggressive than spontaneously occurring ones, and the tumor may invade the adjacent calvarium and extend into the paranasal sinuses (see Image 3).

Spinal meningiomas are also associated with NF2 and are often multiple in number. Unlike intracranial meningiomas, the spinal type calcifies in fewer than 10% of patients (see Image 4).

• Spinal meningiomas are typically intradural and extra-axial but can present as dumbbell-shaped masses extending through the neural foramina. In this situation, distinction from a neurofibroma or schwannoma is difficult, although the schwannoma should be brighter on T2-weighted images.
• Meningiomas are usually isointense relative to the spinal cord on all image sequences and enhance strongly following gadolinium administration.
• Although most spinal meningiomas have a broad dural attachment similar to their intracranial counterparts, dural tail signs are found less frequently in spinal meningiomas.

Spinal ependymomas found in NF2 are divided into 2 groups: those that occur in the upper cord and those that occur in the conus.

• Cord tumors are well-marginated, intensely enhancing lesions, frequently associated with cyst formation and hemorrhage. Ependymomas may be isointense or hypointense relative to the spinal cord on T1-weighted images and are always bright on T2-weighted images, although a peripheral rim of decreased T2 signal has been proposed as being suggestive of ependymoma.
• Conus ependymomas are more often large tumors that can fill the entire spinal canal with heterogeneous signal and enhancement. When small, the tumors may be well-marginated intra-axial lesions, but when larger, they may appear to arise from the extra-axial space.

Multiple extradural masses extending through the neural foramina are found in both NF1 and NF2, although in NF2 (unlike in NF1), these tumors are usually schwannomas. The tumors often have both an intraspinal and an extraspinal component, demonstrate a classic dumbbell shape, and are typically multilevel and bilateral. Signal intensities for spinal schwannomas are the same as those for intracranial schwannomas, and strong contrast enhancement is seen. Because of the multifocality of the spinal schwannomas and an association with scoliosis, coronal MRI often is helpful.

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Degree of Confidence

MRI is the imaging modality of choice in NF2 and is accurate in detecting even small tumors. Separation of intracranial schwannomas from meningiomas may be difficult at times but is usually of little clinical value. The evaluation of the extent, size, and number of intracranial tumors in NF2 is accomplished best by MRI because of its multiplanar capability, its contrast resolution, and the spectrum of pulse sequences, each of which adds different information.

Spinal schwannomas, meningiomas, and ependymomas are also visualized best on MRI. Usually, no other imaging modality is necessary either at the time of diagnosis or as part of a follow-up regimen. Although MRI can image osseous vertebral abnormalities associated with NF2, CT scanning visualizes them better.

Angiography

Findings

Angiography is of limited use in NF2 because most tumors are not visualized. An exception is the "mother-in-law sign" ("arrives early and stays late") of meningioma contrast enhancement. This sign comes from recognition of meningiomas during angiography by their early contrast enhancement and delayed washout. The early contrast enhancement is caused by the enlarged feeding vessels, usually pial or meningeal arteries, and the delayed tumor staining is from lack of capillary blood-brain barriers within the tumor. Unfortunately, like many signs in radiology, this is not specific and can be seen in other hypervascular tumors.

Because ependymomas and schwannomas are not particularly vascular, they are often not visible on angiography; however, when large enough, secondary mass effect on the adjacent brain can be recognized.

• Search for CME/CE on This Topic »

• Neurofibromatosis, Type 2 (Neurology)
• Cafe Au Lait Spots (Pediatrics: General Medicine)
• Neurofibromatosis (Orthopedic Surgery)
• Bell Palsy (Neurology)

• Bevacizumab May Improve Hearing in Neurofibromatosis Type 2

• Surgical Management of Trigeminal Schwannomas
• Malignant Pleural Mesothelioma
• Meningioma and Mobile Phone use - A Collaborative Case-Control Study in Five North European Countries