Intradural extramedullary tumors

Nerve sheath tumors: schwannomas and neurofibromas

This group includes the most common intradural extramedullary neoplasms.

Schwannomas (neurilemomas, neurinomas) These are typical benign tumors (WHO grade 1). As a rule, they grow as a single node and are more frequently detected in adults. If multiple schwannomas are found in a child, this highly likely indicates neurofibromatosis type 2 (NF-2), which increases the risk of malignant transformation.

• Origin and location: the tumor originates from the dorsal (sensory) nerve roots. Most commonly affects the cervical and lumbar spine, less often the thoracic spine.
• Growth patterns: in 70% of cases, the process is localized strictly intradurally extramedullary. About 15% grow extradurally. Another 15% take a specific «dumbbell shape» (dumbbell shape), growing through the intervertebral foramen and occupying both the intra- and extradural spaces.
• MRI semiotics: lesions are usually well encapsulated, sometimes containing a cystic component. On T1-weighted images, they are mostly isointense to the spinal cord tissue (about 20% are moderately hypointense). On T2-weighted images, the signal is hyperintense. Hemorrhages and calcifications are rare. Upon gadolinium administration, strong and homogeneous contrast enhancement is observed, sometimes only weak enhancement along the periphery of the capsule.

Neurofibromas Unlike schwannomas, neurofibromas are poorly encapsulated and are characterized by indistinct margins. They are often multiple, especially in neurofibromatosis type 1 (NF-1), which is characterized by plexiform variants.

• On MRI, a solitary neurofibroma is virtually indistinguishable from a schwannoma.
• On T2-weighted images, they are iso- or hyperintense. A characteristic sign can be the «target» sign (target sign), where a hyperintense rim surrounds a hypo- or isointense center.
• Contrast enhancement is usually weak.
• Malignancy (malignant degeneration) occurs rarely and is associated predominantly with NF-2.

Spinal meningiomas

These are the second most common intraspinal tumors. Meningiomas originate from the dura mater (dural-based) and in >95% of cases are benign (WHO grade 1).

Epidemiology and location Meningiomas are a typical pathology of the elderly (peaking in the 5th and 6th decades of life). In children, they are exceptionally rare, except for patients with NF-2. The tumors are usually solitary (multiple ones occur in only 2% of patients).

• There is a pronounced gender dependence: 80% of all meningiomas are localized in the thoracic region, and the vast majority of them are detected in women (usually growing posterolaterally).
• In men, the picture is different: only 50% of meningiomas are located in the thoracic region, and another 40% in the cervical region (where they more frequently occupy an anterior position).

Due to very slow growth, the spinal cord manages to adapt to compression, so even pronounced compression can be accompanied by minimal clinical symptoms.

Radiological diagnostics

• CT: lesions appear iso- or hyperdense due to cellular density and calcifications. Unlike the brain, vertebral hyperostosis is rare, as epidural fat serves a protective function.
• MRI: on T1-weighted images, meningiomas are iso- or hypointense, and on T2-weighted images, slightly hyperintense. They accumulate gadolinium intensively and homogeneously (except for calcification zones, which remain dark in all sequences and do not enhance). The classic «dural tail» sign (dural tail) can often be visualized.

Differential diagnosis

When evaluating the MRI picture, it is important to be able to distinguish mass lesions from one another, especially if they reach large sizes.

1. Schwannoma or meningioma? If the tumor (e.g., in the cervical region) extends through the intervertebral foramen (neuroforamen) and has a «dumbbell aspect» (dumbbell aspect), involving both the intra- and extradural spaces simultaneously, this indicates a neurinoma. This pattern is clearly visible on axial and coronal slices.
2. Schwannoma or ependymoma? Giant schwannomas at the lumbar level can simulate a myxopapillary ependymoma. Assessing the position of the cauda equina roots (cauda equina) on axial slices helps differentiate them. The filum terminale ependymoma pushes the roots to the periphery of the dural sac, whereas a schwannoma displaces the entire root bundle as a single block to one side (eccentrically).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Leptomeningeal metastases of primary brain tumors in children
• Specifics of neurofibromatosis type 1 and 2 (NF-1, NF-2) in spinal canal tumors
• Myxopapillary ependymoma and other cauda equina neoplasms
• Pathogenesis of the «dural tail» sign formation in meningiomas

Other topics in the "Spine" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.